Branching is a fundamental concept in programming that allows your code to make decisions and execute different blocks of code based on certain conditions. In Python, we achieve branching using various statements, with the most common being:

  • if statement
  • else statement
  • elif statement (else if)

1. if Statement

The if statement is the core of branching. It checks a condition and executes a block of code indented below it only if the condition evaluates to True.

Syntax:

Python
if condition:
    # Code to execute if condition is True
 

Example:

Python
age = 25

if age >= 18:
    print("You are eligible to vote.")
else:
    print("You are not eligible to vote.")
 

2. else Statement

The else statement provides an alternative block of code to execute if the condition in the if statement is False. It's optional and can be used alone after an if statement.

Syntax:

Python
if condition:
    # Code to execute if condition is True
else:
    # Code to execute if condition is False
 

Example (from above):

Python
age = 25

if age >= 18:
    print("You are eligible to vote.")
else:
    print("You are not eligible to vote.")
 

3. elif Statement (else if)

The elif statement (short for "else if") allows you to check multiple conditions sequentially. It's used after an if statement and before an optional else statement. The code block associated with the first elif whose condition evaluates to True will be executed. Subsequent elif statements and the final else block (if present) will be skipped.

Syntax:

Python
if condition1:
    # Code to execute if condition1 is True
elif condition2:
    # Code to execute if condition1 is False and condition2 is True
# ... more elif statements
else:
    # Code to execute if all conditions are False (optional)
 

Example:

Python
grade = 85

if grade >= 90:
    print("Excellent!")
elif grade >= 80:
    print("Very Good!")
elif grade >= 70:
    print("Good!")
else:
    print("Needs Improvement.")
 

Tips for Using Branching Statements:

  • Indentation is crucial in Python. The code block associated with an if, elif, or else statement needs to be indented at the same level (usually with 4 spaces).
  • Make sure your conditions are well-defined and cover all possible scenarios to avoid unexpected behavior.
  • Use clear and meaningful variable names to improve code readability.
  • Consider nesting if statements within other if or elif blocks for more complex decision-making logic.