all Python 3cmathfunction

cmath.log()

powers and logarithms

The natural logarithm of a complex number; the second argument sets the base. The logarithm of a negative number exists here.

Syntax

cmath.log(z[, base])

cmath.log(-1) returns 3.141592653589793j, the principal value, while math.log(-1) raises ValueError. But log(0) is still an error here: ValueError, not -inf. The result is always complex, even cmath.log(100, 10) gives (2+0j); and the logarithm is multivalued, so the function returns only the branch with the imaginary part in (-π, π].

Examples

import cmath
print(cmath.log(-1))  # → 3.141592653589793j
print(cmath.log(100, 10))  # → (2+0j)

import cmath
try:
    cmath.log(0)
except ValueError as e:
    print(type(e).__name__)  # → ValueError

See also

Common errors

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