[Python-ideas] PEP 485: A Function for testing approximate equality

[Guido van Rossum]

I think this looks good and I hope it'll get much approval. Thanks for
hanging in there! I did a quick review:

- Which module should this go into? (I think math, but I don't think you
state it.)

- Sometimes the default relative tolerance is described as 1e-8, sometimes
as 1e-9.

- The formula with "abs(a-b) <= max( ... min(..." is missing an
all-important close parenthesis. I presume it goes before the last comma.
:-)

- What if a tolerance is inf or nan? What if all args are inf or nan?

- I'd argue for allowing the tolerances to be floats even if a and b are
Decimals. There's not much difference in the outcome. Also, what if exactly
one of a and b is Decimal?

- Your language about complex confuses me. What is z? I'd expect the
following behavior:
  - tolerances cannot be complex
  - abs(a-b) is the right thing to use
  Or maybe you meant to say that abs() of the tolerances will be used if
they are complex? That makes some sense in case someone just mindlessly
passes a real cast to complex (i.e. with a zero imaginary part, or
near-zero in case it's the outcome of a very fuzzy computation). But still.
Maybe you can just give the formula to be used for complex args, if it is
in fact any different from the one for reals?

- For unittests are you proposing to replace assertAlmostEquals or
deprecate that and add a new assertIsCloseTo? (I hope the latter.)

- "there as no benefit" -- as->was

-- 
--Guido van Rossum (python.org/~guido)
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