Reference · Math

math.modf

math.modf(num) -> list

What it does

The fractional and the integer part of a number, as a list of two floats, [fraction, whole], as Python's math.modf: math.modf(3.75) is [0.75, 3.0]. Both parts carry the number's sign, so math.modf(-3.75) is [-0.75, -3.0]; the whole part is truncated toward zero, as math.trunc does, but stays a float.

Examples

print(math.modf(3.75), math.modf(-3.75), math.modf(5))let [frac, whole] = math.modf(12.5)print(frac, whole)

[0.75, 3.0] [-0.75, -3.0] [0.0, 5.0]0.5 12.0

Edge cases

• The fraction comes first, the whole part second, as in Python.
• An int gives a fraction of 0.0 and the int as a float.
• A whole negative float gives a fraction of 0.0, not -0.0 as Python gives; the whole part keeps the sign.
• Infinity gives [0.0, inf], and -0.0 gives [0.0, -0.0].
• A float so large that it has no fraction gives 0.0 and the number itself.

print(math.modf(-3.0), math.modf(float("inf")), math.modf(-0.0))print(math.modf(0.5), math.modf(-0.5))

[0.0, -3.0] [0.0, inf] [0.0, -0.0][0.5, 0.0] [-0.5, -0.0]

Errors

An argument that is not a number is a runtime error, not an error value. A decimal is refused with a hint to convert it with float.

print(math.modf("3.75"))

line 1: `math.modf` expects a number as argument 1, got str

Chaining

In a pipeline the number comes first. first and last pick a part:

print(3.75 | math.modf | first)print(3.75 | math.modf | last)print([1.25, 2.5] | map(math.modf))

0.753.0[[0.25, 1.0], [0.5, 2.0]]

See also

math.trunc, math.frexp, math.fmod, int

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