Reference · Math

math.trunc

math.trunc(num) -> int

What it does

The number with its fraction dropped, as an int: rounding toward zero, as Python's math.trunc. math.trunc(3.7) is 3 and math.trunc(-3.7) is -3. An int is itself. It is what int does to a float, but a value that is not a number is a runtime error here rather than an error value.

Examples

print(math.trunc(3.7), math.trunc(-3.7), math.trunc(7))print(math.trunc(2.9) == int(2.9), type_of(math.trunc(2.9)))

3 -3 7true int

Edge cases

• For a positive number it is math.floor; for a negative one it is math.ceil: math.trunc(-0.5) is 0.
• -7 / 2 is -3.5, and truncates to -3.
• A float past what an int holds (2^63, about 9.22 × 10¹⁸) is a runtime error, integer overflow; up to it, an int (math.trunc(9.2e18)).
• math.trunc(a / b) of two ints divides in ints, so it is exact past 2^53, however the call is written (a pipe, a method, the function kept in a variable). A quotient kept in a variable first is a float.

print(math.trunc(-0.5), math.trunc(-7 / 2))print(math.trunc(0.999), math.trunc(-0.999))print(math.trunc(9.2e18), math.trunc(9223372036854775807 / 10))

0 -30 09200000000000000000 922337203685477580

print(math.trunc(-1e19))

line 1: integer overflow

Errors

Infinity and NaN cannot be an int and are a runtime error, not an error value; so is null or any other value that is not a number. A decimal is refused with a hint to convert it with float.

print(math.trunc(null))

line 1: `math.trunc` expects a number as argument 1, got null

Chaining

In a pipeline the number comes first:

print(7.9 | math.trunc)print([1.5, -1.5, 2.5] | map(math.trunc))

7[1, -1, 2]

See also

math.floor, math.ceil, math.modf, int, round

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