Description:

In the world of programming, control flow refers to the order in which statements are executed in a program. It determines how the program flows from one instruction to the next, based on certain conditions or decisions. When it comes to Python, understanding control flow is essential for writing efficient and effective code. In this blog post, we will explore the different aspects of control flow in Python, including conditional statements, loops, and error handling. Whether you’re a beginner or an experienced developer, this comprehensive guide will help you master control flow in Python and enhance your programming skills.

Sections

• Introduction to Control Flow
• Conditional Statements
• Indentation
• if statement
• if-else statement
• if-elif-else statement
• Nested-if statements
• Shorthand if statement
• Comparison operators
• Boolean operators
• The 'is' operator
• The "not" operator

Section 1: Introduction to Control Flow

Control flow is a fundamental concept in programming that allows you to control the execution of statements in your code. In Python, there are several control flow structures that enable you to make decisions, repeat actions, and handle errors. These structures include conditional statements, loops, and exception handling. Let’s dive deeper into each of these aspects of control flow.

Section 2: Conditional Statements

Conditional statements form the basis of control flow in Python. They allow you to execute different blocks of code based on certain conditions. The most commonly used conditional statements in Python are if, elif, and else. The if statement is used to execute a block of code if a specified condition is true. The elif statement allows you to check additional conditions if the previous condition(s) evaluate to false. Finally, the else statement provides a fallback option when none of the conditions are met.

x = 10

if x > 0:
 print("x is positive")
elif x < 0:
 print("x is negative")
else:
 print("x is zero")

In a conditional statement, the keyword if is followed by a condition, such as a comparison of two values. The code block following this header line is only executed if the condition is true. Notice the colon character following the if header. In the following code there is no colon:

Section 3- Indentation

Python recognizes that a block of code is part of a conditional statement if each line of code in the block is indented the same. That is, there should be a bit of whitespace at the beginning of every line of code within the code block. Each line should have the same amount of whitespace.

password = input("Please type in a password: ")

if password == "kittycat":
    print("You knew the password!")
    print("You must be either the intended user...")
    print("...or quite an accomplished hacker.")

print("The program has finished its execution. Thanks and bye!")

You can use the Tab key, short for tabulator key, to insert a set amount of whitespace.Many text editors will automatically indent the following line when the Enter key is pressed after a colon character. When you want to end an indented code block you can use the Backspace key to return to the beginning of the line.

Section 4- if statement:

# if statement
i = 10
if i>5:
    print('i is greater than 5..')

Section 5- if-else statement

i = 1
if i>5:
    print('i is greater than 5..')
else:
    print('i is less than 5')

Section 6- if-elif-else statement

i = 10
if i==5:
    print('i is equal 5..')
elif i==10:
    print('i is equal 10..')
else:
    print('i is other..')

# Program to determine a student's grade based on their marks

marks = int(input("Enter the student's marks: "))

if marks >= 90:
    grade = 'A'
    if marks >= 95:
        distinction = True
    else:
        distinction = False
elif marks >= 80:
    grade = 'B'
    distinction = False
elif marks >= 70:
    grade = 'C'
    distinction = False
elif marks >= 60:
    grade = 'D'
    distinction = False
else:
    grade = 'F'
    distinction = False

print("Grade:", grade)

if distinction:
    print("Distinction achieved!")

# Short hand if statement

i = 10
if i<15: print('i less than 15..')

# Short hand if-else statement

i = 10
print(True) if i==10 else print(False)

# match-case statement

flag = int(input('Enter num: '))

match flag:
    case 5 :
        print('Flag = 5')
    case 10 :
        print('Flag = 10')
    case 15 :
        print('Flag = 15')
    case 20 :
        print('Flag = 20')
    case _ :
        print('Not matched')

Section 8- Comparison operators

Very typically conditions consist of comparing two values. Here is a table with the most common comparison operators used in Python:

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

x = 2
print(x == 2) # prints out True
print(x == 3) # prints out False
print(x < 3) # prints out True

Notice that variable assignment is done using a single equals operator "=", whereas comparison between two variables is done using the double equals operator "==". The "not equals" operator is marked as "!=".

8. 1 - Boolean operators

The "and" and "or" boolean operators allow building complex boolean expressions, for example:

name = "John"
age = 23
if name == "John" and age == 23:
    print("Your name is John, and you are also 23 years old.")

if name == "John" or name == "Rick":
    print("Your name is either John or Rick.")

Section 9- The "in" operator

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

name = "John"
if name in ["John", "Rick"]:
    print("Your name is either John or Rick.")

Python uses indentation to define code blocks, instead of brackets. The standard Python indentation is 4 spaces, although tabs and any other space size will work, as long as it is consistent. Notice that code blocks do not need any termination.

Here is an example for using Python's "if" statement using code blocks:

statement = False
another_statement = True
if statement is True:
    # do something
    pass
elif another_statement is True: # else if
    # do something else
    pass
else:
    # do another thing
    pass

x = 2
if x == 2:
    print("x equals two!")
else:
    print("x does not equal to two.")

A statement is evaulated as true if one of the following is correct: 1. The "True" boolean variable is given, or calculated using an expression, such as an arithmetic comparison. 2. An object which is not considered "empty" is passed.

Here are some examples for objects which are considered as empty: 1. An empty string: "" 2. An empty list: [] 3. The number zero: 0 4. The false boolean variable: False

Section 10-The 'is' operator

Unlike the double equals operator "==", the "is" operator does not match the values of the variables, but the instances themselves. For example:

x = [1,2,3]
y = [1,2,3]
print(x == y) # Prints out True
print(x is y) # Prints out False

Section 10-The "not" operator

print(not False) # Prints out True
print((not False) == (False)) # Prints out False

References

1-Conditional statements

2- 100-Days-of-Code-Data-Science