all Python 3Conditionalsconstruct

if

branching

The conditional statement. It runs a block of code if the condition is true. The condition is any expression Python converts to a bool.

Syntax

if условие:
    блок

The condition need not be a comparison: an empty list, 0, None and "" are all falsy on their own, so "if lst:" reads as "the list is non-empty". Because of that, "if x:" and "if x is not None:" differ — 0 or an empty string fail the first but pass the second.

Examples

x = 5
if x > 0:
    print("положительное")  # → положительное

if "Python" in "Я учу Python":
    print("нашли")  # → нашли

# Пустая коллекция и None — ложь
lst = [1, 2, 3]
if lst:
    print("список не пуст")  # → список не пуст
name = None
if name is None:
    name = "Гость"
print(name)  # → Гость

# Вложенный if
x = 5
if x > 0:
    if x < 10:
        print("однозначное")  # → однозначное

See also

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