Conditional execution in Python directs program flow by evaluating Boolean expressions. Code blocks execute only when their associated condition resolves to True. In Python, any non-zero numerical value or non-empty sequence is considered True; zero, None, and empty sequences evaluate to False.

The foundational if-else construct has this syntax:

if condition:
    # Code block for True condition
else:
    # Code block for False condition

The else clause is optional. Indentation defines the scope of each block.

Example: Basic if-else

is_found = False
item_name = 'laptop'

if item_name == 'desktop':
    is_found = True
    print('Primary device located')
else:
    print(f'Found item: {item_name}')

Relational operators like >, <, ==, >=, and <= are used to form conditions.

Handling Multiple Conditions with elif For checking several distinct values, use elif (short for else-if).

score = 85

if score == 100:
    grade = 'Perfect'
elif score >= 90:
    grade = 'A'
elif score >= 80:
    grade = 'B'
elif score >= 70:
    grade = 'C'
else:
    grade = 'Needs Improvement'

print(f'Grade: {grade}')

Python lacks a switch statement, making if-elif-else the standard for multi-branch logic.

Combining Conditions with Logical Operators Use and and or to create compound conditions.

• and: True only if all conditions are True.
• or: True if at least one condition is True.

value = 7

# Check if value is within a specific range
if value >= 1 and value <= 10:
    print('Value is between 1 and 10')

# Check if value is outside a range
temperature = 25
if temperature < 15 or temperature > 30:
    print('Temperature is uncomfortable')
else:
    print('Temperature is acceptable')

# Complex condition with parentheses for clarity
id = 12
if (id >= 1 and id <= 5) or (id >= 10 and id <= 15):
    print('ID is in the target groups')

Parentheses can explicitly define evaluation order. Relational operators (>, <, etc.) have higher precedence than and/or.

Single-Line Conditional Expression Simple conditionals can be written on one line.

counter = 50
if counter == 50: print('Counter is at midpoint')