1.1 Python

Python is a widely used general-purpose, high level programming language. It was created by Guido van Rossum in 1991 and further developed by the Python Software Foundation. It was designed with an emphasis on code readability, and its syntax allows programmers to express their concepts in fewer lines of code.

Guido Van Rossum

• It is an interpreted, interactive, object-oriented programming language. It incorporates modules, exceptions, dynamic typing, very high level dynamic data types, and classes.

• It’s easy and simple to understand language which feels like reading simple English. This pseudo code nature of Python makes it easy to learn and understand for beginners. Python is a programming language that lets you work quickly and integrate systems more efficiently.

1.2 Features of Python

1.3 General Errors and Debugging

• Programming is a complex process, and because it is done by human beings, it often leads to errors. Programming errors are called bugs and the process of tracking them down and correcting them is called debugging.

• Syntax Errors: Syntax refers to the structure of a program and the rules about that structure.

  • Python is not so forgiving. If there is a single syntax error anywhere in your program, Python will display an error message and quit, and you will not be able to run your program. During the first few weeks of your programming career, you will probably spend a lot of time tracking down syntax errors. As you gain experience, though, you will make fewer errors and find them faster.

• Run-time Errors: Run-time refers to an error that takes place while executing a program.

  As opposed to the compilation errors that occur during a program compilation, runtime errors occur only during the execution of the program. For example, insufficient memory can often trigger a run-time error. The Code that exploded a rocket

• Semantic Errors: If there is a semantic error in a program, it will run successfully, in the sense that the computer will not generate any error messages, but it will not do the right thing. It will do something else. Specifically, it will do what you told it to do.

  • The problem is that the program you wrote is not the program you wanted to write. The meaning of the program (its semantics) is wrong. Identifying semantic errors can be tricky because it requires you to work backward by looking at the output of the program and trying to figure out what it is doing.

• Experimental Debugging: One of the most important skills you will acquire is debugging. Although it can be frustrating, debugging is one of the most intellectually rich, challenging, and interesting parts of programming.

• In some ways, debugging is like detective work. You are confronted with clues, and you have to infer the processes and events that led to the results you see. Its an Iterative Process.

1.4 Installing Python

You may download and install Python from here.

2.1 Modules

Modules refers to a file containing Python statements and definitions. A file containing a python code is called a module. We use modules to break down large programs into small manageable and organized file. In other words, a module is a file containing code written by someone else (usually) which can be imported and used in our program.

• Built in Modules –> Pre installed in Python -> import module_name

  • Some examples of built in modules are random, bdb, calendar, os etc.

• External Modules –> Needs to be installed using PIP -> pip install package_name

  • Some examples of external modules are Pandas, Matplotlib, NumPy etc.

2.2 Preferred Installer Program (PIP)

PIP is package manager for python packages. If you have Python version 3.4 or later, PIP is included by default. Whenever we wants to install a package we may write like:

PIP install package_name

2.3 Comments

A Python comment is line of text in a program that is not executed by the interpreter. Comments can be used during debugging to identify issues and to explain code.

• Single Line Comments –> You can write using #

• Multiple lines Comments –> you can write using ```comment```

print(*objects, sep=' ', end='\n', file=sys.stdout, flush=False)

print("Hello World!") # Single Line Comment

Hello World!

a=2
print('a=', a)  # two objects passed

a= 2

print('a',a, sep='=====', end='') #with seprator and end parameters

a=====2

print('a=',a, sep='', end='\n\n') 

a=2

print('a',a, sep='=====', end='')

a=====2

2.4 Using Python as Calculator

We can use Python as a calculator by typing python + enter on the terminal. This will open Read Evaluate Print Loop (REPL) i.e. >>>.

2.5 Some Arithmetic Operators

5/4

1.25

5%4

1

5//4

1

5**4

625

2.6 Assignment Operators

Assignment operators are used in Python to assign values to variables.

x,y=1,2
print(x,y)

1 2

x=8
x+=2
print(x)

10

x-=3
print(x)

7

x%=3
print(x)

1

#This will not work
a,b=1,2
c="String"
print(a+b)

3

print(a+b+c)

Error in py_call_impl(callable, dots$args, dots$keywords): TypeError: unsupported operand type(s) for +: 'int' and 'str'

Detailed traceback:
  File "<string>", line 1, in <module>

2.7 Conditions / Comparison Operator

Python uses boolean logic to evaluate conditions. The boolean values True and False are returned when an expression is compared or evaluated.

b=(7>4)
c=(7<4)
print(b)

True

print(c)

False

x=5
print(x==5) # Prints out True

True

print(x==2) # prints out False

False

print(x>3)  # Prints out True

True

2.8 Logical Operators

Bool1= True
Bool2= False
print("THe value if Bool1 and Bool2 is: ", (Bool1 and Bool2))

THe value if Bool1 and Bool2 is:  False

print("THe value if Bool1 or Bool2 is: ", (Bool1 or Bool2))

THe value if Bool1 or Bool2 is:  True

print("THe value if not Bool1 is: ", (not Bool1))

THe value if not Bool1 is:  False

print("THe value if not Bool2 is: ", (not Bool2))

THe value if not Bool2 is:  True

2.9 The “in” Operator

The “in” operator could be used to check if a specific object exists within an iterable object container, such as list:

name= "Ahmad"
List = ["Ahmad", "Nadeem"]
print(name in List) # this print True as Ahmad is in the list

True

2.10 Input Function

In Python, we use input() function to take input from the user. Whatever you enter as input, the input function converts it into a string. If you enter an integer value still input() function convert it into a string.

a = input(" Please enter your name: ")

print(a) # Try yourself

2.11 Glossary

algorithm

A set of specific steps for solving a category of problems.

bug

An error in a program.

comment

Information in a program that is meant for other programmers (or anyone reading the source code) and has no effect on the execution of the program.

debugging

The process of finding and removing any of the three kinds of programming errors.

exception

Another name for a runtime error.

formal language

Any one of the languages that people have designed for specific purposes, such as representing mathematical ideas or computer programs; all programming languages are formal languages.

high-level language

A programming language like Python that is designed to be easy for humans to read and write.

immediate mode

A style of using Python where we type expressions at the command prompt, and the results are shown immediately. Contrast with script, and see the entry under Python shell.

interpreter

The engine that executes your Python scripts or expressions.

low-level language

A programming language that is designed to be easy for a computer to execute; also called machine language or assembly language.

natural language

Any one of the languages that people speak that evolved naturally.

object code

The output of the compiler after it translates the program.

parse

To examine a program and analyze the syntactic structure.

portability

A property of a program that can run on more than one kind of computer.

print function

A function used in a program or script that causes the Python interpreter to display a value on its output device.

problem solving

The process of formulating a problem, finding a solution, and expressing the solution.

program

a sequence of instructions that specifies to a computer actions and computations to be performed.

Python shell

An interactive user interface to the Python interpreter. The user of a Python shell types commands at the prompt (>>>), and presses the return key to send these commands immediately to the interpreter for processing. The word shell comes from Unix. In the PyScripter used in this RLE version of the book, the Interpreter Window is where we’d do the immediate mode interaction.

runtime error

An error that does not occur until the program has started to execute but that prevents the program from continuing.

script

A program stored in a file (usually one that will be interpreted).

semantic error

An error in a program that makes it do something other than what the programmer intended.

semantics

The meaning of a program.

source code

A program in a high-level language before being compiled.

syntax

The structure of a program.

syntax error

An error in a program that makes it impossible to parse — and therefore impossible to interpret.

token

One of the basic elements of the syntactic structure of a program, analogous to a word in a natural language.

2.12 Exercise

1. Write a program to print a multiple lines string in Python.

2. Using the Python interpreter, type 1 + 2 and then hit return. Python evaluates this expression, displays the result, and then shows another prompt. * is the multiplication operator, and ** is the exponentiation operator. Experiment by entering different expressions and recording what is displayed by the Python interpreter.

3. Type 1 2 and then hit return. Python tries to evaluate the expression, but it can’t because the expression is not syntactically legal. Instead, it shows the error message:

   {python, error=TRUE, include=TRUE} #print(1 2)

   In many cases, Python indicates where the syntax error occurred, but it is not always right, and it doesn’t give you much information about what is wrong. So, for the most part, the burden is on you to learn the syntax rules.

   In this case, Python is complaining because there is no operator between the numbers.

4. Write a program to display a user entered word “Easy” followed by “Python is very” using input() function.

5. Type cheese without the quotation marks. This is a run-time error; specifically, it is a NameError, and even more specifically, it is an error because the name cheese is not defined.

6. Install an External Module named pandas.

7. Write a program to print the contents of a directory using os module. Hint: Search online for the function which does so i.e how do i list all files of a directory.

8. Perform some arithmetic using REPL.

9. Use comparison operators to find out whether a given variable ‘a’ is greater than ‘b’ or not. consider a=45 and b=35.

10. Write a program to find out average of two numbers entered by the user.

11. Write a program which accepts the radius of a circle from the user and compute the area.

12. How to find the reminder of a given number?

3.1 Variable

A Python variable is a reserved memory location to store values. In other words, a variable in a python program gives data to the computer for processing.

help("keywords")

Here is a list of the Python keywords.  Enter any keyword to get more help.

False               class               from                or
None                continue            global              pass
True                def                 if                  raise
and                 del                 import              return
as                  elif                in                  try
assert              else                is                  while
async               except              lambda              with
await               finally             nonlocal            yield
break               for                 not                 

3.2 Variable Types in Python

Every value in Python has a datatype. Different data types in Python are Integers, Floating point numbers, Strings, Boolean, List, Tuple, Dictionary, etc. Variables in Python can be declared by any name or even alphabets like a, aa, abc, etc.

• A variable name can contain alphabets, digits and underscores

• A variable name can start with alphabets or an underscore

• Variable name is case sensitive

• A variable name can’t start with a number/digit

• Spaces are not allowed in variable name

a=10
print(a)

10

x , y = 5 ,6
print(x,y)

5 6

b=c=d=30
print(b,c,d)

30 30 30

a=10
print(type(a))

<class 'int'>

b=10.1
print(type(b))

<class 'float'>

c="State Bank of Pakistan"
print(type(c))

<class 'str'>

d=True
print(type(d))

<class 'bool'>

e=None
print(type(e))

<class 'NoneType'>

#declare a variable and initialize it
a=10
# re-declaring the variable 
a="State Bank of Pakistan"
print(a)

State Bank of Pakistan

print("a"+10) # we can't concatenate string with integer

Error in py_call_impl(callable, dots$args, dots$keywords): TypeError: can only concatenate str (not "int") to str

Detailed traceback:
  File "<string>", line 1, in <module>

print("a" + "10")

a10

n=100 # an integer
print(type(n))

<class 'int'>

f=float(n)
print(type(f))

<class 'float'>

s=str(n)
print(type(s))

<class 'str'>

f=10.5 #a float
print(type(f))

<class 'float'>

n=int(f)
print(type(n))

<class 'int'>

s=str(f)
print(type(s))

<class 'str'>

3.3 Exercise

1. Guess the type of 6/2, 6//2 and check the results.

2. What is the value of x after the following is run:
   
   x=4
   
   x=x/2

3. Create a variable named carname and assign the value toyota to it.

4. Assign: 3 to variable glass_of_water and printout the message “I drank 3 glasses of water today” by using variable name.

5. Let’s try to see what happens after assigning a new value to our variable. Note that program gets executed line by line.

   glass_of_water=3

   glass_of_water=glass_of_water + 1

   print()

6. Check the type of the variable define above.

7. Type Cast the above variable first into float and then to string.

8. Define a variable a =3 and A=‘NIBAF’. Will ‘A’ overwrite ‘a’?

9. Check the type of a variable assigned using input() function.

10. Calculate square of the number entered by the user.

11. Write a program to accept two numbers from the user and calculate multiplication.

12. Display string “My”, ‘Name’, “Is”, “Python” as “My**Name**Is**Python” Hint: Default separator in print function is space i.e. ” “.

13. Write a program to take three names as input from a user in the single input() function call.

14. Define a complex variable. 😎

4.1 String Indexing

Individual characters of a string can be accessed directly using a numeric index.

• String indexing in python is zero-based.

  • The first character in the string has index 0.

  • The next has index 1 . . . and so on.

  • The index of the last character will be length of the string minus 1.

4.2 Slicing Strings

You can return a range of characters by using the slice syntax. Specify the start index and the end index, separated by a colon in \[ \], to return a part of the string. i.e. we can get a part of the string using slicing.

4.3 Syntax : \[Start : Stop : Step\]

• Start: First Index of the sub-string you want to extract.

• Stop: Last Index of the sub-string you want to extract.

• Step: The size of the jump you want to take while extracting the subsection.

4.4 Scenarios

Scenario 1: No step size Scenario 2: No stop index Scenario 3: No start index

Scenario 4: No start and stop index Scenario 5: No strat, step or stop index

Scenario 6: Single charachter as a string

A = "Welcome to the World of Python"
print(A[3:7]) # by default step size is 1

come

print(A[24:]) # python will assume last index of string as the stop index

Python

print(A[:7])  #python assume the start index as 0

Welcome

print(A[::2]) # python will give every second chanracter from complete string

Wloet h ol fPto

print(A[::])  # start=0, stop=last index, step=1 by deafult

Welcome to the World of Python

print(A[0:1]) # [start:start+1:1]

W

s='NIBAF'
t = s[:]
print(id(s))

1486119600

print(id(t))

1486119600

4.5 Concatenating the Strings

String concatenation means add strings together. Use the + character to add a variable to another variable:

x = "Python Eats"
y= "???"
z = x+y
print(z)

Python Eats???

4.6 String Functions

string.capitalize()

a = "    Python is Easy   "
b = ":".join(["Ahmad", "Nadeem"])
c = "Ahmad Nadeem".split()
print(a.upper())

    PYTHON IS EASY   

print(a.endswith('y'))

False

print(a.find('n'))

9

print(a.replace("Python" , "Jython"))

    Jython is Easy   

print(a.strip())

Python is Easy

print(b)

Ahmad:Nadeem

print(c)

['Ahmad', 'Nadeem']

4.7 Escape Sequence Characters

In Python, escape sequences are indicated by a backslash ( \ ).

4.8 Formatted String Literal or f-string

n = 5
m = 10
prod = n*m
print('The product of', n, 'and', m, 'is', prod)

# this can be reproduced by using f-string as:

The product of 5 and 10 is 50

print(f'The product of {n} and {m} is {prod}')

The product of 5 and 10 is 50

4.9 Exercise

1. Convert the String "welcome to the beautiful world of python" to "Welcome To The Beautiful World Of Python"

2. Find the output of the following:

   str1 = "PYnative"
   print(str1[1:4], str1[:5], str1[4:], str1[0:-1], str1[:-1])

3. Guess the output of the following:

   # print('python \n cpython')
   # print('python \t cpython')
   # print('python \\ cpython')

4. if a=‘1’ and b=‘2’ what will be the value of c=a+b?

5. Consider the variable g, and find the first index of the sub-string snow:

   g = “Mary had a little lamb Little lamb, little lamb Mary had a little lamb \ Its fleece was white as snow And everywhere that Mary went Mary went, Mary went \ Everywhere that Mary went The lamb was sure to go”

6. In the above variable g, replace the sub-string Mary with Bob:

7. What is the result of following?
   “hello Mike”.find(“Mike”)

8. If string=‘Welcome’ then how to get output as WelcomeWelcomeWelcome?

9. Ask the name and favorite fruit from two persons using input and return as a single string. like: Ahmad likes Mangoes and Muhammad likes Oranges.

10. Write a program to detect double spaces in a string.

11. Replace the double spaces in above question with a single space.

12. Write a program to format the following letter using escape sequence characters.

    letter = ” Dear Participants, This Python course is nice. Thanks!”

13. Find the length of the word NIBAF.

14. Print the reversed str = ‘NIBAF’

15. Attempt to index beyond the end of the string results and checkout the result. like ,‘Ahmad\[6\]’

16. Select the every third letter from the str = ‘I am learning python’

17. How to check the given word, sentence or a number is palindrome!

    A word, verse, or sentence (such as ‘Able was I ere I saw Elba’) or a number (such as 1881) that reads the same backward or forward is called palindrome.

18. Write a program which accepts the user’s first and last name then print in reverse order.

19. Write a program to accept a filename from user and print the name and extension of that file.

5.1 Creating a Lists

items = [1,2,3]
items1 = list('123')
items2=['123']
items3=[]
items3.append(7)
items2.append(8) # adds at the end of the list
items4=[1, 2, False, [4,5]]
print(items, items1, items2, items3, items4)

[1, 2, 3] ['1', '2', '3'] ['123', 8] [7] [1, 2, False, [4, 5]]

myList = ['milk', 'cars', 14, False]
myList[0]

'milk'

myList[-1]

False

myList[0::2]

['milk', 14]

myList = ['milk', 'cars', 14, False]
myList[1] = 'Trucks'
myList

['milk', 'Trucks', 14, False]

myList.insert(2,9)
myList

['milk', 'Trucks', 9, 14, False]

5.2 Sorting List

The list.sort() method sorts the elements of a list in ascending or descending order:

a= [4,1,2,7,5,3]
a.sort()
print(a)

[1, 2, 3, 4, 5, 7]

a.sort(reverse=True)
print(a)

[7, 5, 4, 3, 2, 1]

cities = ['Karachi', 'Lahore', 'Faisalabad', 'Hayderababd']
cities.sort(key=len)
print(cities)

['Lahore', 'Karachi', 'Faisalabad', 'Hayderababd']

cities.sort(key=len, reverse=True)
print(cities)

['Hayderababd', 'Faisalabad', 'Karachi', 'Lahore']

cities = ['Karachi', 'Lahore', 'Faisalabad', 'Hayderababd']
cities.pop(0) # will delete the value at index 0 an return its value

'Karachi'

cities

['Lahore', 'Faisalabad', 'Hayderababd']

cities.remove('Lahore')
cities

['Faisalabad', 'Hayderababd']

cities2= cities.copy() #create a copy of list

5.3 Converting a String to a List

String can be convert to a list, as per spaces ” ” or any other special characters “_”, according to the users choice, are encountered. To do this we use the split() method.

string = "I like Python"
print(string.split(" "))

['I', 'like', 'Python']

string1 = "I_Like_Python"
print(string1.split("_"))

['I', 'Like', 'Python']

5.4 Tuples

Tuples are collections of Python objects. They are similar to lists but the difference between them is that tuples are immutable while lists are mutable. Tuples are created by typing a sequence of items, separated by commas. Optionally, you can put the comma-separated values in parenthesis.

1. Tuple1=(1,2,5,6)

2. Tuple2=(‘a’, “b”, ‘c’, “d”)

3. Tuple3 = () #empty tuple

4. Tuple4 = 5,3,1

5. Tuple5 = (“London”, “Tokyo”, “Korea”, 1986, 1640, 1948)

   Note: To create a single item tuple, you have to use a comma after the value.

Tup1 = (5) # its not a tuple
Tup2 = (5,)
Tuple5 = ("London", "Tokyo", "Korea", 1986, 1640, 1948)
print(type(Tup1))

<class 'int'>

print(type(Tup2))

<class 'tuple'>

print(Tuple5.index("Korea"))

2

The values of tuples are stored at different index positions starting from zero. We can access the values by using their index positions inside square brackets. We can index or slice tuples like lists.

a = (1, 2, 2, 1, 3, 1, 4,2)

print(a[0]) , print(a[4])

1
3
(None, None)

print(a.count(2)) # will return the number of times 2 occurs

3

print(a.index( 2)) # will return the index of first occurrence of 2

1

5.5 Tuple Unpacking

With a special syntax, Python can unpack the values of a tuple and extract them into single variables.

a,b,c = (1,2,3)
print(a)

1

print(b)

2

print(c)
 #or

3

coordinates = (4,5,6)
x,y,z = coordinates # same can be used to unpack a list
print(x)

4

The number of variables to the left and right side should be the same and it assigns each variable respectively.

5.6 Lists Vs Tuples

list = [2,3,5,7,11,13,17]
print(dir(list))

['__add__', '__class__', '__class_getitem__', '__contains__', '__delattr__', '__delitem__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__iadd__', '__imul__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__rmul__', '__setattr__', '__setitem__', '__sizeof__', '__str__', '__subclasshook__', 'append', 'clear', 'copy', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']

tuple = (1,4,9,16,25,36)
print(dir(tuple))

['__add__', '__class__', '__class_getitem__', '__contains__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__getnewargs__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__rmul__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'count', 'index']

import sys
print(help(sys.getsizeof))

Help on built-in function getsizeof in module sys:

getsizeof(...)
    getsizeof(object [, default]) -> int
    
    Return the size of object in bytes.

None

list  = [1,2,3,4,5,6,7]
tuple = (1,2,3,4,5,6,7)
print("The Size of the List  is", sys.getsizeof(list ), 'bytes')

The Size of the List  is 120 bytes

print("The Size of the Tuple is", sys.getsizeof(tuple), 'bytes')

The Size of the Tuple is 96 bytes

import timeit
list_test = timeit.timeit(stmt="[1,2,3,4,5,6]", number=1000_000)
tuple_test = timeit.timeit(stmt="(1,2,3,4,5,6)", number=1000_000)
print('Time needed to make 1000000 lists: ', list_test)

Time needed to make 1000000 lists:  0.06933149999531452

print('Time needed to make 1000000 tuples: ', tuple_test)

Time needed to make 1000000 tuples:  0.013147399993613362

5.7 Exercise

1. Create a list a_list, with the following elements 1, hello, [1,2,3] and True.

2. Find the first and last value of the list.

3. Find the value stored at index 1 of a_list.

4. Retrieve the elements stored at index 1, 2 and 3 of a_list.

5. Concatenate the following lists A = [1, 'a'] and B = [2, 1, 'd']

6. Make the list of the PIN of 5 officers and sort them in ascending and descending order.

7. Consider the following tuple and Find the length of the tuple, genres_tuple genres_tuple = (“pop”, “rock”, “soul”, “hard rock”, “soft rock”, “R&B”, “progressive rock”, “disco”)

8. Access the element, with respect to index 3.

9. Use slicing to obtain indexes 3, 4 and 5.

10. Find the index of "disco".

11. Generate a sorted List from the Tuple C_tuple=(-5, 1, -3).

12. Check that a python tuple can’t be altered.

13. Find the sum of list2 = [1,2,3,4].

14. Write a program to count the number of occurrences of 4 in tuple1=(4,1,2,5,7,4,8,4,4)

15. Reverse a list2 define above (Q.13) using index method.

16. Make the list of the words of “I am doing well”

17. sort the above created list as per length of the words in reverse order.

18. list1 = [100, 200, 300, 400, 500], output = [500,400,300,200,100]

19. list2 = [10, 20, [300, 400, [5000, 6000], 500], 30, 40], Expected output :

    [10, 20, [300, 400, [5000, 6000, 7000], 500], 30, 40]

20. list1 = ["a", "b", ["c", ["d", "e", ["f", "g"], "k"], "l"], "m", "n"] # sub list to add sub_list = ["h", "i", "j"] Expected Output:

    ["a", "b", ["c", ["d", "e", ["f", "g","h","i","j"], "k"], "l"], "m", "n"]

21. list1 = [5, 10, 15, 20, 25, 50, 20] Expected Output: [5, 10, 15, 200, 25, 50, 20]

22. list1 = [5, 20, 15, 200, 25, 50, 220] remove 20 from the list.

6.1 Dictionaries

Like a real-life dictionary has words and meanings, Python dictionaries have keys and values. Dictionaries in Python are collections that are unordered, indexed and mutable. They hold keys and values.

They are in curly brackets. Key-value pairs are separated by commas and keys and values are separated by colons. Keys in dictionaries are unique and immutable. You can search for a value if you know the key. One key cannot have two values.

Financial_Dictionary = {"Key": "Value", "Key": "Value1", "SBP" : "State Bank of Pakistab", "BSC" : "Banking Services Corporation", "PSPC" : "Pakistan Security Printing Corporation", "NIBAF" : "National Institute of Banking and Finance", 'Marks' : [71, 78, 84]}
print(type(Financial_Dictionary))

<class 'dict'>

print(Financial_Dictionary)

{'Key': 'Value1', 'SBP': 'State Bank of Pakistab', 'BSC': 'Banking Services Corporation', 'PSPC': 'Pakistan Security Printing Corporation', 'NIBAF': 'National Institute of Banking and Finance', 'Marks': [71, 78, 84]}

print(Financial_Dictionary['Marks'])

[71, 78, 84]

del(Financial_Dictionary['BSC']) # will del key=BSC
print(Financial_Dictionary)

{'Key': 'Value1', 'SBP': 'State Bank of Pakistab', 'PSPC': 'Pakistan Security Printing Corporation', 'NIBAF': 'National Institute of Banking and Finance', 'Marks': [71, 78, 84]}

print('BSC' in Financial_Dictionary) # as it already deleted , Results in False

False

6.2 Nested Dictionaries and Dictionary Methods

Dict = {'1' : 'One', '2':'Two', "Dict1" : {'3': 'Three', '4' : 'Four'} }
print(Dict['1'])

One

print(Dict['Dict1']['4'])

Four

Dict['1'] = 'i' # Immutable i.e. we can change 
print(Dict)

{'1': 'i', '2': 'Two', 'Dict1': {'3': 'Three', '4': 'Four'}}

print(Dict.keys()) # will show the keys of a dictionary

dict_keys(['1', '2', 'Dict1'])

print(Dict.values()) #will show the value of a dictionary

dict_values(['i', 'Two', {'3': 'Three', '4': 'Four'}])

print(Dict.items()) # print the (key : value) for all contents of Dictionary

dict_items([('1', 'i'), ('2', 'Two'), ('Dict1', {'3': 'Three', '4': 'Four'})])

new_dict = {'Hello' : 'World'}
Dict.update(new_dict) # will append new_dict in Dict
print(Dict)

{'1': 'i', '2': 'Two', 'Dict1': {'3': 'Three', '4': 'Four'}, 'Hello': 'World'}

print(Dict['9']) # returns error if not in Dict

Error in py_call_impl(callable, dots$args, dots$keywords): KeyError: '9'

Detailed traceback:
  File "<string>", line 1, in <module>

print(Dict.get('9')) # return None

None

Quick Quiz: Write a program to ask a phone number in digits and translate them like: 123 One Two Three.

# Phone = input ("Number Please: ")
phone = "123"
Digit_Dict = {
    "1" : "One",
    "2" : "Two",
    "3" : "Three",
    "4" : "Four"
}
output = ""
for numbers in phone:
    output += Digit_Dict.get(numbers, "!") + " "
print(output)

One Two Three 

Quick Quiz: Get a message from input method and resturn the same message with translated emoji like “:)” to 😊.

#message = input(">")
message = "I am happy :)"
words = message.split()
# print(words)
emoji_dict = {
     ":)" : "😊",
     ":(" : "😒"
 }
trans_message = "" 
for word in words:
    trans_message += emoji_dict.get(word, word)+ " "
print(trans_message)

I am happy 😊 

6.3 Sets

Sets in Python are a collection of unordered and unindexed Python objects. Sets are mutable, iterable and they do not contain duplicate values. It is similar to the concept of the mathematical set. That is, set is a collection of non-repetitive elements. The elements in a set are declared inside curly braces separated by commas.

a = {2,1,3,4,2,5,6,3,8}
type(a)

<class 'set'>

print(a)

{1, 2, 3, 4, 5, 6, 8}

b = {}  # check the type of a
c = set() # an empty set
type(c)

<class 'set'>

c.add (2)
c.add (5)
print(c)

{2, 5}

Since the sets are unindexed, we cannot use slicing or indexing on sets, it will give us a TypeError error when using indexing.

6.4 Operations on Sets

c = {1,2,3}
c.add([1,2,3]) # we can't add list and dictionaries in a set

Error in py_call_impl(callable, dots$args, dots$keywords): TypeError: unhashable type: 'list'

Detailed traceback:
  File "<string>", line 1, in <module>

c.add((1,2,3))# we can add tuple 
print(c)

{1, 2, 3, (1, 2, 3)}

print(len(c)) # prints the length of set c

4

c.remove(2)  # removes 2 from  set c
print(c) 

{1, 3, (1, 2, 3)}

print(c.pop()) # removes any arbitrary number from  set c and return the value

1

print(c)

{3, (1, 2, 3)}

c.update({8,9})
print(c)

{3, 8, 9, (1, 2, 3)}

6.5 Exercise

1. The Swift, City and Civic have the following prices in thousands 2800, 3500, 6200 respectively. Create a dictionary car_price_dict where the keys are the car name and the price in thousands are the values.

2. You will need this dictionary for the next two questions: Dict= {‘SBP_ACT’: ‘1956’, ‘BCO’:‘1962’}

   In the Dict, what are the keys?

3. In the Dict, what are the values?

4. Use the dictionary find the price of the City.

5. Find the names of the cars from the dictionary using the method keys()

6. Find the prices of the cars from the dictionary using the method values()

7. Create a dictionary of Urdu words with values as their English translation. Provide user an option to look it up.

8. Consider the list A = [1, 2, 2, 1] and set B = set([1, 2, 2, 1]), does sum(A) == sum(B)?

9. Create a new set C that is the union of sets A={1, 2, 3, 4} and B={3, 4, 5, 6}.

10. Find out if A is a subset of C.

11. Write a program to add an element in a set.

12. Write a program to add more than one element in a set.

13. Write a program to remove items from a given set.

14. Write a program to create an intersection of set.

15. Write a program to create a union of sets.

16. Write a program to input 5 numbers from the user and display all the unique numbers

17. Can we have a set with elements 3 and ‘3’ ?

18. What is the type of s = { }?

19. What will be the length of set s:

    s = set(), s.add(1), s.add(1.0), s.add(‘1’)

20. Create a dictionary. Allow 4 users to enter their favorite Fruits as value , ans use their names as keys. Assume names are unique.

21. If names of 2 users are same in above problem, what will happen?

22. If fruit options of 2 users are same in above problem, what will happen?

23. Check if a set is a subset of another set using comparison operator and isubset() operator.

24. Write a Python program to print out a set containing all the colors from color1 which are not present in color2.

    color1 = set(["White","Black", "Red"])

    color2 = set(["Red", "Green"]), Expected Output:{'Black','White'}

25. Provide a use case for each of the following Python data structures: tuple, list, and dictionary.  Explain why each use case is appropriate for each data structure as opposed to the others.

    List - A shopping list. The list type is appropriate, since it can be changed.

    Tuple - The first 7 prime numbers. A tuple is a suitable structure, because it is a immutable data type.

    Dictionary - A list of words and their meanings. Since a dictionary is made up by key-value pairs, the key would be the word and the value would assume it’s meaning.

    Set - A list of registered e-mails in a system. It’s a proper way to store them, for the e-mails must each be unique.

26. Ask the phone number from a user, and convert integers into strings like: 1 to one.

27. Creat a dictionary of animal names as keys and their pictures as values. Hint: to get picture/emoji’s press window+period(.)

28. Take input from user to show the picture of the animal. Also provide to look at the names of the animals in the dictionary.

29. If animal’s picture is not in the dictionary, provide the option to add the name and picture in the dictionary on run time.

7.1 If else Statement Syntax

x=1
if x==1:
    print("x is 1") # this is body of if or statement
#else:
 #   print("x is not 1") # this is body of elif

x is 1

Here, the program evaluates the test expression and will execute statement(s) only if the test expression is True. If the test expression is False, the statement(s) is not executed.

In Python, the body of the if statement is indicated by the indentation. The body starts with an indentation and the first unindented line marks the end.

Remember: Python interprets non-zero values as True. None and 0 are interpreted as False.

7.2 Indentation

Python uses indentation for blocks, instead of curly braces. Both tabs and spaces are supported, but the standard indentation requires standard Python code to use four spaces. For example:

x=1
if x==1:
    #indented four spaces
    print("x is 1")
else:
    print("x is not 1")

x is 1

If statement, without indentation (will raise an error).

7.3 If elif and else Statement

x=-1
if x==1:
    #indented four spaces
    print("x is 1") # this is body of if or statement
elif x<0:
  print("x is less than zero")
else:
    print("x is not 1") # this is body of elif

x is less than zero

#n = int(input(" Please enter the number: "))
n=32
if n>=25:
  print("Yes")
else:
  print("No")

Yes

#n = int(input(" Please enter the number: "))
n = -4
if n>0:
  print("Number is +ve")
elif n==0:
  print("Number is zero")
else:
  print("Number is -ve")

Number is -ve

7.4 Nested if statements

We can have a if...elif...else statement inside another if...elif...else statement. This is called nesting in computer programming.

Any number of these statements can be nested inside one another. Indentation is the only way to figure out the level of nesting. They can get confusing, so they must be avoided unless necessary.

Example: Write a program to check if a number entered by the user is positive or negative or zero and display an appropriate message using nested if statement.

#n = int(input(" Please enter the number: "))
n = 3
if n>=0:
  if n==0:
    print("Number is zero")
  else:
    print("Number is +ve")
else:
  print("Number is -ve")

Number is +ve

7.5 Multiple If Conditions

n1 = 4 #n1 = int(input(" Enter the First Number : "))
n2 = 3 #n2 = int(input(" Enter the 2nd  Number : "))
n3 = 2 #n3 = int(input(" Enter the 3rd Number : "))
n4 = 1 #n4 = int(input(" Enter the 4th Number : "))

if n1>n2:
    f1 = n1
else:
   f1 = n2
if n3>n4:
   f2 = n3
else:
    f2 = n4
if f1>f2:
    print(f" The Largest Number is : {f1} ")
else:
    print(f" The Largest Number is : {f2} ")

 The Largest Number is : 4 

7.6 Exercise

1. Write a program to check whether a user entered number is odd or even?

2. Take two numbers from user and print larger.

3. Take three numbers from user, and print the largest.

4. Write a program to check whether a user entered number is odd or even,valid only for first 10 natural numbers.

5. write a program to get the difference b/w a given number and 17, if number is greater than 17, return double the absolute difference.

6. Write a program to calculate the sum of three given numbers, if values are equal then return thrice of their sum.

7. Write a prog. to get a new string from a given string where “Is” has been added to the front. if the given string already begins with “Is” then return the string.

8. If Question mark ‘?’ is missing in above string, then also include the ‘?’ at the end.

9. Write a program to find out whether a given post is talking about “SBP” or not.

   1. Write a program to find out whether a student is fail or pass? if it require total 40% and at-least 33% in each subject to pass. Assume 3 subjects, input from the user and marks are out of 100.

10. Write a program to detect a spam (OSICO Spam detector), a spam comment is defined as a text containing following keywords:

    “make a lot of money”, “buy now”, “subscribe this”, “click this”. Write a program to detect these spams.

11. Write a program to calculate the grade of an officer from his numeric rating from the following scheme: greater than 4.5 implies A, greater than 3.5 implies B+, greater than 3 implies B and else C.

12. Write a program to find out the type of the variable Var1 = ——-. suppose 1+2j check whether it is int, float, str, bool, complex, tuple, dict, list, or unknown.

13. Write a Python program to sum of three given integers. However, if two values are equal sum will be zero.

14. Write a program to calculate the fare of a journey based on the following conditions, fare will be charged Rs. 15/km for first 100km, for next 200km it will be Rs.14/km, for next 200km it will be Rs.12/km and for distance above 500km, it will be charged Rs.11/km.

15. Write a routine to convert weight from Kg to pounds or pounds to kg.

8.1 The “for” loop

For loop iterate over a given sequence (range, list, tuple, string etc.) or other iterable objects. Iterating over a sequence is called traversal. Flow chart of for loop is:

8.2 Looping through String

Even strings are iterable objects, they contain a sequence of characters:

for letter in 'string':
  print(letter)

s
t
r
i
n
g

8.3 Looping through a List

Banks = ['ABL', 'MCB', 'NBP']
for bank in Banks:
  print(bank)

ABL
MCB
NBP

8.4 How to Use Index

Banks = ['ABL', 'MCB', 'NBP']
for i in range(3):
  print(i, Banks[i])

0 ABL
1 MCB
2 NBP

8.5 Use of Enumerate for Indexing

# Loop through the list and iterate on both index and element value

squares=['red', 'yellow', 'green', 'purple', 'blue']

for i, square in enumerate(squares):
    print(i, square)

0 red
1 yellow
2 green
3 purple
4 blue

We can change the elements in a list:

# Use for loop to change the elements in list

squares = ['red', 'yellow', 'green', 'purple', 'blue']

for i in range(0, 5):
    print("Before square ", i, 'is',  squares[i])
    squares[i] = 'white'
    print("After square ", i, 'is',  squares[i])

Before square  0 is red
After square  0 is white
Before square  1 is yellow
After square  1 is white
Before square  2 is green
After square  2 is white
Before square  3 is purple
After square  3 is white
Before square  4 is blue
After square  4 is white

Quick Quiz: Print the following pattern using for loop.

+++

++

+++++

+++

+++++++++

list = [3,2,5,3,9]
for i in list:
  print('+'*i)

+++
++
+++++
+++
+++++++++

8.6 Iterating over tuples

We can use for loops to iterate on a tuple. The for loop will keep on iterating until the elements in the tuples are exhausted.

Tuple = ('SBP', 'NIBAF', 'BSC')
for entities in Tuple:
  print(entities)

SBP
NIBAF
BSC

8.7 The range ( ) function

When using for loops in Python, the range() function is pretty useful to specify the number of times the loop is executed. It yields a sequence of numbers within a specified range.

syntax: range (start, stop, steps)

• The first argument is the starting value. It is zero by default.

• The second argument is the ending value of the range.

• The third argument is the number of steps to take after each yield.

# for loop
for i in range(2,10,3):
  print(i)

2
5
8

for char in 'SBP':
  print(char)
else:
  print('loop ended')

S
B
P
loop ended

8.8 Nested Loop

A nested loop is a loop inside a loop. The “inner loop” will be executed once for each iteration of the “outer loop” i.e., in each iteration of the outer loop, inner loop execute all its iteration. For each iteration of an outer loop, the inner loop re-start and completes its execution before the outer loop can continue to its next iteration.

list1 = ['Rizwan', 'Adil', 'Ahmad']
list2 = ['JD', 'OG-4', 'SBP']
for officer in list1:
    for x in list2:
        print(f'({officer}, {x})')

(Rizwan, JD)
(Rizwan, OG-4)
(Rizwan, SBP)
(Adil, JD)
(Adil, OG-4)
(Adil, SBP)
(Ahmad, JD)
(Ahmad, OG-4)
(Ahmad, SBP)

Quick Quiz: Create Co-ordinate (0,0) ,(0,1) ,(0,2) , (1,0) ,(1,1) ,(1,2) ,(2,0) ,(2,1) ,(2,2) ,(3,0) ,(3,1) ,(3,2)

for x in range(4):
  for y in range(3):
    print(f"({x},{y})")

(0,0)
(0,1)
(0,2)
(1,0)
(1,1)
(1,2)
(2,0)
(2,1)
(2,2)
(3,0)
(3,1)
(3,2)

8.9 The “while” loop

The while loop in Python executes a block of code until the specified condition becomes False.

Flow chart of while loop is :

count = 0 # Initializing, To Give an initial value to a variable
while count<10: # Setting a condition
  print(count)
  count+=2 # Incrementing the initial value by 2

0
2
4
6
8

In the example, the while statement checks if count is less than 10.

Initially, count is zero so the statement is true and it executes the body of while. Then the count gets incremented by 2. Again we check the condition and this goes on till the condition becomes false.

Here, when our code checks 10<10, the statement returns False and so the code in while block is not executed.

# While Loop Example

dates = [1982, 1980, 1973, 2000]

i = 0
year = dates[0]

while(year != 1973):    
    print(year)
    i = i + 1
    year = dates[i]
    

1982
1980

print("It took ", i ,"repetitions to get out of loop.")

It took  2 repetitions to get out of loop.

8.10 Infinite loop

A loop is called an infinite loop when the loop will never reach its end.

Usually, when a condition is always True in a while loop, the loop will become an infinite loop. So we should be careful when writing conditions and while updating variables used in the loop.

In Python shell, we can stop/terminate the program on an infinite loop by using CTRL + C. In jupyter notebook press i twice.

Quick Quiz: Write a program to print 1 to 50 using a while loop.

Quick Quiz: Write a program to print the contents of a list=['C', 'C++', 'java', 'fortran','python'] using while loop.

8.11 Loop control statements in Python

num = 0
while num<10:
  num +=1
  if num==5:
    break
  print(num)

1
2
3
4

In this loop, we are incrementing the value of num variable and then printing it. When the num value becomes 5 the break statement is executed which terminates the loop and therefore loop is not executed further.

num = 0
while num<10:
  num +=1
  if num==5:
    continue
  print(num)

1
2
3
4
6
7
8
9
10

Here, we see that when the num variable is equal to 5, the continue statement is executed. It then doesn’t execute the lines after the continue statement and the control is sent to the next iteration.

8.12 Common Mistakes

1. Mostly people forgte to initialize the variable.

2. There is second issue, we might face if we forget to initialize the variables with the right value. we might have already used the variable in our program. if we reuse a variable without setting the correct value from the start, it will still have the value from before.

x=1
sum = 0
while x<10:
  sum+=x
  x+=1
print(sum)

45

Whenever you are writing a loop, check that you are initializing all the variables you want to use before you use them.

product = 1
x=1
while x<10:
  product=product*x
  x+=1
print(product) # what we call this outcome!

362880

8.13 Exercise

1. A list of groceries is given below, print all items with its index.

   groceries = ["bananas","butter","cheese","toothpaste"]

2. Make a combination of all the letters of ‘SBP’ and ‘NIBAF’

3. Write a program to say “hello” to all persons in a list which starts with M. List = ['Ahmad', 'Muhammad', 'Essa', 'Mossa']

4. Print odd numbers in first 10 numbers using while loop.

5. Also find the sum of all numbers in above question.

6. Write a program to print the multiplication table of a number entered by the user, using ‘for’ loop.

7. Attempt above problem using while loop.

8. Find the total of [10,20,30] using for loop.

9. Write a program to guess a secrete number in 3 attempts using while loop.

10. Solve above problem while generating secrete number randomly.

11. Provide a hint to make problem easy, if guess is larger, then print ‘its larger’, otherwise ‘its smaller’

12. Write a program whether a given number is prime or not.

13. Find the prime numbers in a given range.

14. store the numbers obtained in above question as a list.

15. Find the sum of all the numbers in the list above in question 14.

16. Challenge: calculate the time required to run the above code 500 times.

17. Draw the following pattern using nested loop.

    #    xxxxx
    #    xx
    #    xxxxx
    #    xx
    #    xx

18. Make the co-ordinates (0,0,0) …(2,2,2) using nested for loop.

19. Write a for loop the prints out all the element between -5 and 5 using the range function.

20. Write a while loop to display the values of the Rating of an album playlist stored in the list PlayListRatings. If the score is less than 6, exit the loop. The list PlayListRatings is given by: PlayListRatings = [10, 9.5, 10, 8, 7.5, 5, 10, 10]

21. Write a program to sum first n natural numbers, take input from user.

22. Write program to find the factorial of a number n.

23. Write a program to print the following pattern.
    

    *
    * *
    * * *
    * * * *
    * * * * *

24. Write a Python program to concatenate all elements in a list into a string and return it

25. Write a nested for loop program to print multiplication table in Python from 2 to 10.

26. Write a Python program to print all even numbers from a given numbers list in the same order and stop the printing if any numbers that come after 237 in the sequence.

    numbers = [386, 462, 47, 418, 907, 344, 236, 375, 823, 566, 597, 978, 328, 615, 953, 345, 399, 162, 758, 219, 918, 237, 412, 566, 826, 248, 866, 950, 626, 949, 687, 217, 815, 67, 104, 58, 512, 24, 892, 894, 767, 553, 81, 379, 843, 831, 445, 742, 717, 958,743, 527]

27. Write a program to find those numbers which are divisible by 7 and multiple of 5, between 1500 and 2700 (both included) and print the result in the form of a list.

9.1 Example

Iterating through a string Using for Loop

n_letters = []
for letter in 'NIBAF':
  n_letters.append(letter)
  
print(n_letters)

['N', 'I', 'B', 'A', 'F']

Iterating through a string Using List Comprehension

n_letters=[letter for letter in 'NIBAF']

print(n_letters)

['N', 'I', 'B', 'A', 'F']

If you noticed, ‘NIBAF’ is a string, not a list. This is the power of list comprehension. It can identify when it receives a string or a tuple and work on it like a list.

9.2 Example

Based on a list of fruits, you want a new list, containing only the fruits with the letter “a” in the name.

Without list comprehension you will have to write a for statement with a conditional test inside:

fruits = ['apple', 'banana', 'kiwi','mango', 'cherry']
fruits_a = []
for fruit in fruits:
  if 'a' in fruit:
    fruits_a.append(fruit)
print(fruits_a)

['apple', 'banana', 'mango']

This can be done in one line of code With list comprehension:

fruits = ['apple', 'banana', 'kiwi','mango', 'cherry']
fruits_a = [fruit for fruit in fruits if 'a' in fruit]

print(fruits_a)

['apple', 'banana', 'mango']

9.3 The Syntax

new_list = [expression for item in iterable if condition == True]

The return value is a new list, leaving the old list unchanged.

9.4 Key Points to Remember

• List comprehension is an elegant way to define and create lists based on existing lists.

• List comprehension is generally more compact and faster than normal functions and loops for creating list.

• However, we should avoid writing very long list comprehensions in one line to ensure that code is user-friendly.

• Remember, every list comprehension can be rewritten in for loop, but every for loop can’t be rewritten in the form of list comprehension.

9.5 Exercise

1. Create the list [1,2,3,4,5] using list comprehension.

2. Use a list comprehension that iterates over a_list, prints a list composed of each value in a_list multiplied by 10.

   a_list = list(range(1, 11))

3. Use a list comprehension that iterates over a_list, prints a list composed of odd numbers from 1 to 9.

4. Using a list comprehension which iterates over a_list and whose output expression accesses a value from a dictionary, print a list composed of the text form of each even number from 2 to 10, e.g., [ 'two', 'four', 'six', 'eight', 'ten' ].

   a_dictionary = { 1 : 'one', 2 : 'two', 3 : 'three', 4 : 'four', 5 : 'five', 6 : 'six', 7 : 'seven', 8 : 'eight', 9 : 'nine', 10 : 'ten'}

5. Prompt the user for a number, which will be returned from input as a string data type. Strings can be iterated over like lists, such that the loop repeats for each character in the string. Using a list comprehension which iterates over the user-entered string and whose output expression accesses values from a_dictionary, print a list of the text form of each digit from the user-entered string, e.g., Enter a number: 195 return [ 'one', 'nine', 'five' ]

6. Using the same user-entered number and list comprehension as above, also print the text form of the digits in a single string (using the string join function) with a dash between each text form of the digit, e.g.,

   one-nine-five

7. Write a list comprehension that builds a list containing only the names with at least 4 characters. list9 = ['SBP', 'NIABF', 'HoK', 'PSPC', 'DPC']

8. Write a list comprehension that builds a list containing only even numbers over 40.

   numbers = list (range (10,50,5))

9. Add % in front and end of every single word in a given string str: “Fall is Awesome in Sakardu” only using list comprehensions. Desired Output

   ['%Fall%','%is%','%Awesome%','%in%','%Sakardu%']

10. Use list comprehension to make a list of the first letter of each word in the following list:

    wordList = ["this", "is", "an", "apple"]

11. A string is given:

    msg = "Long Live Pakistan!"

    Write a list comprehension that prints a list

    ['L', 'o', 'n', 'g', 'L', 'i', 'v', 'e', 'P', 'a', 'k', 'i', 's', 't', 'a', 'n']

    Do not print out the space or the !.

10.1 Function

A function is a group of related statements that performs a specific task.

Functions help break our program into smaller and modular chunks. As our program grows larger and larger, functions make it more organized and manageable. Furthermore, it avoids repetition and makes the code reusable any number of time.

def function_name(parameters):
    """docstring"""
    statement(s)

def greet(name):
  '''Greeting Function'''
  print("Welcome to the World of Python, " +name)
greet("Raja")

Welcome to the World of Python, Raja

10.2 Type of functions

Basically, we can divide functions into the following two types:

1. Built-in functions - Functions that are built into Python.

2. User-defined functions - Functions defined by the users themselves.

For example, len( ), range ( ) and print( ) are built-in functions, and the greet function defined above is a user-defined function.

10.3 Functions with arguments

def greet1(name,msg):
  print("Hello", name +', '+msg)
greet1('ahmad', 'how are you')

Hello ahmad, how are you

Here, the function greet1() has two parameters.

Since we have called this function with two arguments, it runs smoothly and we do not get any error.

If we call it with a different number of arguments, the interpreter will show an error message. Below is a call to this function with one and no arguments along with their respective error messages.

def greet1(name,msg):
  print("Hello", name +', '+msg)
greet1('ahmad')

Error in py_call_impl(callable, dots$args, dots$keywords): TypeError: greet1() missing 1 required positional argument: 'msg'

Detailed traceback:
  File "<string>", line 1, in <module>

10.4 Default argument or parameter value

Function arguments can have default values in Python. We can provide a default value to an argument by using the assignment operator (=). Here is an example.

def greet1(name ,msg="How do you do"):
  print("Hello", name +', '+msg)
greet1('Ahmad')

Hello Ahmad, How do you do

The input to a function is called a formal parameter.

A variable that is declared inside a function is called a local variable. The parameter only exists within the function (i.e. the point where the function starts and stops).

A variable that is declared outside a function definition is a global variable, and its value is accessible and modifiable throughout the program.

def square(a): # formal parameter
  '''
  This function will return the sqaure of number plus 1
  
  '''
  b = 1 # local variable
  c = a*a + b
  return c

print(square(2))
  

5

10.5 Recursive function

Recursion is the process of defining something in terms of itself. That is, a function that calls itself. For example:

factorial(n)=n * factorial(n-1)

#n! = 1*2*3*...*n
n=3
product = 1
for i in range(n):
  product = product*(i+1)
print(product)

6

def fact(n):
  product = 1
  for i in range(n):
    product=product*(i+1)
  return product
print(fact(3))

6

def recur_factorial(n):
    """This is a recursive function
    to find the factorial of an integer"""
    if n==1:
        return 1
    else:
        return (n*recur_factorial(n-1))


print(recur_factorial(3))

6

10.6 Pre-defined Functions

There are many pre-defined functions in Python, so let’s start with the simple ones.

The print() function:

# Build-in function print()

list1 = [10.0, 8.5, 9.5, 7.0, 7.0, 9.5, 9.0, 9.5] 
print(list1)

[10.0, 8.5, 9.5, 7.0, 7.0, 9.5, 9.0, 9.5]

The sum() function adds all the elements in a list or tuple: try pease

The len() function show the length a list or tuple: try please

10.7 Exceptions

An exception is an error that occurs during the execution of code. This error causes the code to raise an exception and if not prepared to handle it will halt the execution of the code.

1/0

Error in py_call_impl(callable, dots$args, dots$keywords): ZeroDivisionError: division by zero

Detailed traceback:
  File "<string>", line 1, in <module>

y = a+5

Error in py_call_impl(callable, dots$args, dots$keywords): TypeError: unsupported operand type(s) for +: 'set' and 'int'

Detailed traceback:
  File "<string>", line 1, in <module>

a = [1,2,3]
a[5]

Error in py_call_impl(callable, dots$args, dots$keywords): IndexError: list index out of range

Detailed traceback:
  File "<string>", line 1, in <module>

10.8 Exercise_Functions

1. Create a function con that add two number .

2. Can the con function we defined before be used to concatenate lists or tuples?

3. Write a function named odd_or_zero which takes one parameter, a number, and returns that number if it is odd or returns 0 if the number is even. Then using a list comprehension which iterates over a_list and calls your odd or zero function for each value, print a list like the following: [ 1, 0, 3, 0, 5, 0, 7, 0, 9, 0 ]

4. Define a function to find the greatest of three numbers using.

5. How do you prevent python print( ) function to print a new line at the end.

6. Write a recursive function to calculate the sum of first n natural numbers.

7. Write a function to print first n lines of the following pattern.
   *****
   ***
   *

8. Write a function which converts inches in cm

9. Write a function to remove a given word from a string and strip it at the same time.

10. Write a Python function that takes a list and returns a new list with unique elements of the first list. Sample List : [1,2,3,3,3,3,4,5], Unique List :[1, 2, 3, 4, 5]