pythonmathroundingsignificant-digits

How to round a number to significant figures in Python


I need to round a float to be displayed in a UI. e.g, to one significant figure:

1234 -> 1000

0.12 -> 0.1

0.012 -> 0.01

0.062 -> 0.06

6253 -> 6000

1999 -> 2000

Is there a nice way to do this using the Python library, or do I have to write it myself?


Solution

  • You can use negative numbers to round integers:

    >>> round(1234, -3)
    1000.0
    

    Thus if you need only most significant digit:

    >>> from math import log10, floor
    >>> def round_to_1(x):
    ...   return round(x, -int(floor(log10(abs(x)))))
    ... 
    >>> round_to_1(0.0232)
    0.02
    >>> round_to_1(1234243)
    1000000.0
    >>> round_to_1(13)
    10.0
    >>> round_to_1(4)
    4.0
    >>> round_to_1(19)
    20.0
    

    You'll probably have to take care of turning float to integer if it's bigger than 1.