Truncate to three decimals in Python

You can use the following function to truncate a number to a set number of decimals:

import math
def truncate(number, digits) -> float:
    # Improve accuracy with floating point operations, to avoid truncate(16.4, 2) = 16.39 or truncate(-1.13, 2) = -1.12
    nbDecimals = len(str(number).split('.')[1]) 
    if nbDecimals <= digits:
        return number
    stepper = 10.0 ** digits
    return math.trunc(stepper * number) / stepper

Usage:

>>> truncate(1324343032.324325235, 3)
1324343032.324

I've found another solution (it must be more efficient than "string witchcraft" workarounds):

>>> import decimal
# By default rounding setting in python is decimal.ROUND_HALF_EVEN
>>> decimal.getcontext().rounding = decimal.ROUND_DOWN
>>> c = decimal.Decimal(34.1499123)
# By default it should return 34.15 due to '99' after '34.14'
>>> round(c,2)
Decimal('34.14')
>>> float(round(c,2))
34.14
>>> print(round(c,2))
34.14

About decimals module

About rounding settings

You can use an additional float() around it if you want to preserve it as a float.

%.3f'%(1324343032.324325235)