Python Conditional Statements: Notes

Introduction

  • Decision-making is crucial in programming, just as it is in life.
  • Conditional statements automate decision-making in Python.
  • Python evaluates conditions as True or False:
    • If True, the specified block of code executes.
    • If False, another block of code is executed.

Types of Conditional Statements in Python

  1. If Statement
  2. If-Else Statement
  3. If…Elif…Else Ladder
  4. Nested If Statement
  5. Short Hand If Statement
  6. Short Hand If-Else Statement

1. If Statement

  • The simplest decision-making statement.
  • Executes a block of code if the condition is True.

Syntax:

if condition:
    statement

Example:

num = 5
if num > 0:
    print(num, "is a positive number.")

Output:
5 is a positive number.

2. If-Else Statement

  • Used when both True and False parts are specified.
  • Executes one block of code if the condition is True and another if False.

Syntax:

if condition:
    # Code for true condition
else:
    # Code for false condition

Example:

num = 5
if num >= 0:
    print("Positive or Zero")
else:
    print("Negative number")

Output:
Positive or Zero

3. If…Elif…Else Ladder

  • Evaluates multiple conditions in a sequence.
  • Executes the first condition that is True.
  • If none are True, the else block executes.

Syntax:

if condition:
    # Code for condition 1
elif condition:
    # Code for condition 2
else:
    # Code for no conditions true

Example:

num = 7
if num > 0:
    print("Positive number")
elif num == 0:
    print("Zero")
else:
    print("Negative number")

Output:
Positive number

4. Nested If Statement

  • Allows multiple layers of decision-making.
  • An if statement inside another if statement.

Syntax:

if condition1:
    if condition2:
        # Code for both conditions true
    else:
        # Code if condition1 is true, condition2 is false
else:
    # Code if condition1 is false

Example:

num = 8
if num >= 0:
    if num == 0:
        print("Zero")
    else:
        print("Positive number")
else:
    print("Negative number")

Output:
Positive number

5. Short Hand If Statement

  • Used when there is only one statement in the if block.
  • Everything is written in a single line.

Syntax:

if condition: statement

Example:

i = 15
if i > 11: print("i is greater than 11")

Output:
i is greater than 11

6. Short Hand If-Else Statement

  • Combines if and else in a single line.
  • Executes one statement for True and another for False.

Syntax:

statement_if_true if condition else statement_if_false

Example 1:

a = 3
b = 5
print("A") if a > b else print("B")

Output:
B

Example 2 (with 3 conditions):

a = 3
b = 5
print("A is greater") if a > b else print("=") if a == b else print("B is greater")

Output:
B is greater

Key Takeaways

  • If Statement: Executes code if a condition is true.
  • If-Else Statement: Executes different code for true or false conditions.
  • If…Elif…Else Ladder: Evaluates multiple conditions in sequence.
  • Nested If Statement: Allows decision-making within another condition.
  • Short Hand If Statement: Simplifies single-line true condition execution.
  • Short Hand If-Else Statement: Combines if and else in a single line.

Conclusion

  • Mastering conditional statements is fundamental for learning Python.
  • They form the basis of decision-making in programs.
  • Begin with these basics to build robust and dynamic Python applications.