all Python 3cmathfunction

cmath.isnan()

checking

Checks whether at least one part of a complex number is NaN. Comparing with == does not work for this.

Syntax

cmath.isnan(z)

NaN equals nothing, not even itself, so z == cmath.nan and z == cmath.nanj are always False: a check with == silently lets NaN through. For a complex value the function looks at both parts: complex(1, nan) is NaN, although its real part is fine.

Examples

import cmath
z = complex(1, float('nan'))
print(z == z, cmath.isnan(z))  # → False True
print(cmath.nanj == cmath.nanj)  # → False

See also

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