[Python-Dev] Symmetry arguments for API expansion (original) (raw)

Nick Coghlan ncoghlan at gmail.com
Wed Mar 21 08:34:27 EDT 2018

On 14 March 2018 at 08:29, Tim Peters <tim.peters at gmail.com> wrote:

[Tim] >> An obvious way to extend it is for Fraction() to look for a special >> method too, say "asintegerratio()".

[Greg Ewing] > Why not asintegerratio? Because. at this point, that would be beating a dead horse ;-)

I'm not so sure about that, as if we define a protocol method for it, then we'd presumably also define an "operator.as_integer_ratio" function, and that function could check index in addition to checking the new protocol method.

For example:

def as_integer_ratio(n):
    # Automatically accept true integers
    if hasattr(n, "__index__"):
        return (n.__index__(), 1)
    # New reserved protocol method
    if hasattr(n, "__integer_ratio__"):
        return n.__integer_ratio__()
    # Historical public protocol method
    if hasattr(n, "as_integer_ratio"):
        return n.as_integer_ratio()
    # Check for lossless integer conversion
    try:
        int_n = int(n)
    except TypeError:
        pass
    else:
        if int_n == n:
            return (int_n, 1)
    raise TypeError(f"{type(n)} does not support conversion to an

integer ratio")

Similarly, on the "operator.is_integer" front:

def is_integer(n):
    # Automatically accept true integers
    if hasattr(n, "__index__"):
        return True
    # New reserved protocol method
    if hasattr(n, "__is_integer__"):
        return n.__is_integer__()
    # Historical public protocol method
    if hasattr(n, "is_integer"):
        return n.is_integer()
    # As a last resort, check for lossless int conversion
    return int(n) == n

Cheers, Nick.

P.S. I've suggested "operator" as a possible location, since that's where we put "operator.index", and it's a low level module that doesn't bring in any transitive dependencies. However, putting these protocol wrappers somewhere else (e.g. in "math" or "numbers") may also make sense.

-- Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20180321/690d1b39/attachment.html>

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