What is the best way to compare floats for almost-equality in Python?

Question

It\'s well known that comparing floats for equality is a little fiddly due to rounding and precision issues.

For example: https://randomascii.wordpress.com/2012/02/2

Answer 1

Useful for the case where you want to make sure 2 numbers are the same 'up to precision', no need to specify the tolerance:

• Find minimum precision of the 2 numbers

• Round both of them to minimum precision and compare

def isclose(a,b):                                       
    astr=str(a)                                         
    aprec=len(astr.split('.')[1]) if '.' in astr else 0 
    bstr=str(b)                                         
    bprec=len(bstr.split('.')[1]) if '.' in bstr else 0 
    prec=min(aprec,bprec)                                      
    return round(a,prec)==round(b,prec)                               

As written, only works for numbers without the 'e' in their string representation ( meaning 0.9999999999995e-4 < number <= 0.9999999999995e11 )

Example:

>>> isclose(10.0,10.049)
True
>>> isclose(10.0,10.05)
False