Python if else and conditional logic

Conditional Flow

Conditionals let your program take different paths based on a value. The colon and indented block are mandatory.

score = 72

if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
elif score >= 70:
    grade = "C"
else:
    grade = "F"

print(grade)  # C

Truthy and Falsy

Python evaluates any value as boolean in a condition. Falsy values: 0, 0.0, "", [], {}, None, False. Everything else is truthy.

name = ""
if name:
    print("Hello,", name)
else:
    print("No name provided")  # runs

Ternary Expression

For a single-line conditional assignment, use the ternary form. Keep it readable — do not nest ternary expressions.

x = 10
label = "even" if x % 2 == 0 else "odd"
print(label)  # even

Avoid deeply nested if blocks. If nesting exceeds two levels, consider restructuring with early returns or helper functions.

Conditionals are the decision-making backbone of any program. Keep your conditions simple and readable — if a condition needs a comment to explain it, extract it into a well-named boolean variable. Deeply nested if-blocks are a sign the logic should be refactored, often with early returns or guard clauses. Python does not have a switch/match statement in older versions, but Python 3.10 introduced match for structural pattern matching, which is powerful for dispatching on data structures. For now, elif chains are idiomatic and readable.