Round to significant figures in python

Question

I want to round like this 42949672 -> 42949700, 2147483647 -> 2147480000, 4252017622 -> 4252020000 etc.

I tried to use following , but only works for the first one. How can I make a more general one? thanks

round(42949672, -2)

Answer 1

The accepted answer has limitations and does not produce technically correct significant figures in the general case.

numpy.format_float_positional supports the desired behaviour directly. The following fragment returns the float x formatted to 4 significant figures, with scientific notation suppressed.

import numpy as np
x=12345.6
np.format_float_positional(x, precision=4, unique=False, fractional=False, trim='k')
> 12340.