Truthy vs Falsy Values in Python

Truthy vs Falsy Values in Python

In Python, truthy and falsy values are concepts used to determine the truth value of an expression in a Boolean context, such as conditionals and loops.

Falsy Values: A value is considered "falsy" if it evaluates to False when used in a Boolean context. The following are considered falsy in Python:

  1. None
  2. False
  3. Zero of any numeric type: 0, 0.0, 0j
  4. Empty sequences and collections: '' (empty string), () (empty tuple), [] (empty list), {} (empty dictionary), set() (empty set)
  5. Any custom class instances which implement a __bool__ or __len__ method that returns False or 0.

Truthy Values: Any value that's not falsy is considered truthy. This means that in a Boolean context, it will evaluate to True. This includes:

  1. True
  2. All numbers not equal to zero (e.g., 1, -2, 3.5, 1+2j)
  3. Non-empty strings (e.g., 'hello')
  4. Non-empty sequences and collections (e.g., (1,), [1, 2, 3], {'a': 1})
  5. Custom class instances which do not implement __bool__ or __len__ or where those methods return something that is not False or 0.

Here's a quick example to demonstrate truthy and falsy values:

# Falsy values print(bool(None)) # False print(bool(False)) # False print(bool(0)) # False print(bool(0.0)) # False print(bool(0j)) # False print(bool('')) # False print(bool([])) # False print(bool(())) # False print(bool({})) # False print(bool(set())) # False # Truthy values print(bool(True)) # True print(bool(1)) # True print(bool(-1)) # True print(bool(1.1)) # True print(bool(1+1j)) # True print(bool('False')) # True, because it's a non-empty string print(bool([0])) # True, because it's a non-empty list print(bool((0,))) # True, because it's a non-empty tuple print(bool({'a': 0})) # True, because it's a non-empty dictionary class CustomClass: def __bool__(self): return True print(bool(CustomClass())) # True

Understanding truthy and falsy values is crucial when writing conditionals (if, while) or when using logical operations (and, or, not), as well as when applying Boolean logic to control flow and other aspects of program behavior.

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