[issue25412] __floordiv__ in module fraction fails with TypeError instead of returning NotImplemented

[Sergey Shashkov]

Sergey Shashkov  added the comment:

This patch actually fixes the problem:

https://bugs.python.org/issue35588
https://github.com/python/cpython/commit/3a374e0c5abe805667b71ffaaa7614781101ff4c




from fractions import Fraction
import operator

class Goo:
__radd__, __rdivmod__, __rfloordiv__, __rmod__, __rmul__, __rpow__, 
__rsub__, __rtruediv__ = [lambda a, b: 'ok'] * 8

for func in operator.add, operator.sub, operator.mul, operator.truediv, 
operator.pow, operator.mod, operator.floordiv, divmod:
print(func.__name__, func(Fraction(1), Goo()))

--
nosy:  -mark.dickinson, oscarbenjamin, vstinner
pull_requests: +11085
resolution:  -> fixed
stage:  -> patch review
status: open -> closed

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue25412] __floordiv__ in module fraction fails with TypeError instead of returning NotImplemented

[Sergey Shashkov]

Sergey Shashkov added the comment:

OK,

then we should not change numbers.py.

And in fractions.py:

def __floordiv__(a, b):
"""a // b"""
if isinstance(b, numbers.Complex) or hasattr(b, '__rtruediv__'):
fr = a / b
if fr != NotImplemented:
return math.floor(a / b)
else:
return NotImplemented
else:
return NotImplemented

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue25412] __floordiv__ in module fraction fails with TypeError instead of returning NotImplemented

[Sergey Shashkov]

Sergey Shashkov added the comment:

Bad idea, just


def __floordiv__(a, b):
"""a // b"""
if isinstance(b, numbers.Complex):
return math.floor(a / b)
else:
return NotImplemented

If b is inherited from number, real, complex, Fraction and etc, then a of type 
Fraction knows, how do make a division.
Otherwise may be b has __rfloordiv__, that khows how to be divided by Fraction.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue25412] __floordiv__ in module fraction fails with TypeError instead of returning NotImplemented

[Oscar Benjamin]

Oscar Benjamin added the comment:

You should test the change with number types that don't use the number tower 
e.g. Decimal, sympy, gmpy2, mpf, numpy arrays etc. Few non stdlib types use the 
number ABCs so testing against numbers.Complex may cause a change in behaviour.

--
nosy: +oscarbenjamin

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue25412] __floordiv__ in module fraction fails with TypeError instead of returning NotImplemented

[Sergey Shashkov]

Changes by Sergey Shashkov :


--
hgrepos:  -320

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue25412] __floordiv__ in module fraction fails with TypeError instead of returning NotImplemented

[Sergey Shashkov]

Changes by Sergey Shashkov :


--
hgrepos: +320

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue25412] __floordiv__ in module fraction fails with TypeError instead of returning NotImplemented

[Sergey Shashkov]

Sergey Shashkov added the comment:

...
def forward(a, b):
if isinstance(b, (int, Fraction)):
return monomorphic_operator(a, b)
elif isinstance(b, float):
return fallback_operator(float(a), b)
elif isinstance(b, complex):
return fallback_operator(complex(a), b)
else:
return NotImplemented
forward.__name__ = '__' + fallback_operator.__name__ + '__'
forward.__doc__ = monomorphic_operator.__doc__

def reverse(b, a):
if isinstance(a, numbers.Rational):
# Includes ints.
return monomorphic_operator(a, b)
elif isinstance(a, numbers.Real):
return fallback_operator(float(a), float(b))
elif isinstance(a, numbers.Complex):
return fallback_operator(complex(a), complex(b))
else:
return NotImplemented
...
so division is possible only with int, Fraction, float, complex, 
numbers.Rational, numbers.Real, numbers.Complex.
For all of them "isinstance(b, numbers.Complex)" is true

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue25412] __floordiv__ in module fraction fails with TypeError instead of returning NotImplemented

[Sergey Shashkov]

Changes by Sergey Shashkov :


--
hgrepos: +321
keywords: +patch
Added file: http://bugs.python.org/file40797/fractions_truediv_fix.patch

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue25412] __floordiv__ in module fraction fails with TypeError instead of returning NotImplemented

[Sergey Shashkov]

New submission from Sergey Shashkov:

__floordiv__ in module fraction fails with TypeError instead of returning 
NotImplemented when modulo is a class without __rtruediv__ or __mul__.

Code sample:

class Foo(object):
def __rdivmod__(self, other):
return 'rdivmod works'

from fractions import Fraction
a = Fraction(1,1)
b = Foo()
print(divmod(1, b))
print(divmod(a, b))



__divmod__ in Fraction is inherited from class Real (numbers.py):
def __divmod__(self, other):
return (self // other, self % other)

So __floordiv__ and __mod__ are called. 

def __floordiv__(a, b):
"""a // b"""
return math.floor(a / b)

def __mod__(a, b):
"""a % b"""
div = a // b
return a - b * div

__floordiv__ if fractions.py makes a true division, and __mod__ makes 
multiplication.



The following code will fix the problem:


def __divmod__(self, other):
if isinstance(a, numbers.Complex):
return (self // other, self % other)
else:
return NotImplemented

--
components: Library (Lib)
messages: 253046
nosy: ShashkovS
priority: normal
severity: normal
status: open
title: __floordiv__ in module fraction fails with TypeError instead of 
returning NotImplemented
type: behavior
versions: Python 2.7, Python 3.2, Python 3.3, Python 3.4, Python 3.5, Python 3.6

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue25412] __floordiv__ in module fraction fails with TypeError instead of returning NotImplemented

[STINNER Victor]

STINNER Victor added the comment:

Can you please write a patch? See https://docs.python.org/devguide/

--
nosy: +haypo

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue25412] __floordiv__ in module fraction fails with TypeError instead of returning NotImplemented

[R. David Murray]

Changes by R. David Murray :


--
nosy: +mark.dickinson

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue25412] __floordiv__ in module fraction fails with TypeError instead of returning NotImplemented

[Sergey Shashkov]

Sergey Shashkov added the comment:

def __floordiv__(a, b):
"""a // b"""
if isinstance(b, numbers.Complex):
return math.floor(a / b)
else:
return NotImplemented

And the same for __mod__.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com