assert — Advanced Examples

Debugging aid that tests a condition and raises AssertionError if false

EasyIntermediateAdvancedExpert

Assert pitfalls

Common mistakes with assert statements.

python
# PITFALL 1: assert with a tuple is always True!
# assert(condition, "message")  <-- WRONG! This is assert (tuple,)
# assert condition, "message"   <-- RIGHT

try:
    x = -1
    assert x > 0, "Must be positive"
except AssertionError as e:
    print(f"Caught: {e}")

# Tuple form is always truthy (non-empty tuple)
value = (False, "this is always truthy")
print(f"Tuple truthiness: {bool(value)}")

# PITFALL 2: assert is a statement, not a function
# These are different:
# assert(False, "msg")  -> asserts a non-empty tuple (always True!)
# assert False, "msg"   -> asserts False with message "msg"

# Demonstrate the difference
try:
    assert False, "correct usage"
except AssertionError as e:
    print(f"Correct: {e}")

The most common assert pitfall is writing assert(cond, msg) with parentheses — this creates a non-empty tuple which is always truthy. Use assert cond, msg without parens.

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