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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/2012/02/25/comparing-floating-point-numbers-2012-edition/
What is the recommended way to deal with this in Python?
Surely there is a standard library function for this somewhere?
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To compare two floating point values, we have to consider the precision in to the comparison. For example, if two numbers are 3.1428 and 3.1415, then they are same up to the precision 0.01, but after that, like 0.001 they are not same.
Python unittest – assertAlmostEqual() function assertAlmostEqual() in Python is a unittest library function that is used in unit testing to check whether two given values are almost equal or not. This function will take five parameters as input and return a boolean value depending upon the assert condition.
Using the == Operator As a result, we can't have an exact representation of most double values in our computers. They must be rounded to be saved. In that case, comparing both values with the == operator would produce a wrong result.
Python 3.5 adds the math.isclose and cmath.isclose functions as described in PEP 485.
If you're using an earlier version of Python, the equivalent function is given in the documentation.
def isclose(a, b, rel_tol=1e-09, abs_tol=0.0): return abs(a-b) <= max(rel_tol * max(abs(a), abs(b)), abs_tol) rel_tol is a relative tolerance, it is multiplied by the greater of the magnitudes of the two arguments; as the values get larger, so does the allowed difference between them while still considering them equal.
abs_tol is an absolute tolerance that is applied as-is in all cases. If the difference is less than either of those tolerances, the values are considered equal.
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Is something as simple as the following not good enough?
return abs(f1 - f2) <= allowed_error If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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