Python – How do I future-validate ’round’ functions in Python2?

When round is imported from the future, it behaves differently than the Python3 round function. Specifically, it does not support negative rounding.

In Python3:

>>> round(4781, -2)
4800

In Python2:

>>> from builtins import round
>>> round(4781, -2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/dist-packages/future/builtins/newround.py", line 33, in newround
    raise NotImplementedError('negative ndigits not supported yet')
NotImplementedError: negative ndigits not supported yet

Possible solutions include error handling for negative rounding, writing my own round function, etc. How should it be handled? (implicitly, I ask for best practices, most Pythonic, accepted by the community, etc.).

I’m going to suggest your custom function idea so you can make sure it always does what you want, but this seems like a special (weird) case if I don’t use future.builtin.round() I get it

python 3.6:

>>> round(4781, -2)
4800

and Python 2.7:

>>> round(4781, -2)
4800.0

It just seems that future.builtins is corrupted in some way; In this case, you should avoid using the future.builtins.round() function. Note that py3 round() returns an integer and py2 round() returns a float, but this seems to be the only difference between the two stock implementations (for simple rounding operations such as the example given).