Stub for fractions #94

youtux · 2016-02-26T16:24:42Z

I was trying to create the stub for the Python 3.4 statistics module, but it depends on the fractions module.
So here is my attempt for the fractions module, any suggestion accepted.

youtux · 2016-02-26T16:41:19Z

Done, thank you @matthiaskramm

youtux · 2016-02-26T16:51:29Z

Hmm, I don't really know how to deal with the first error:

running mypy  # with 207 files
stdlib/2and3/fractions.pyi: note: In class "Fraction":
stdlib/2and3/fractions.pyi:26: error: Signature of "__round__" incompatible with supertype "Real"

Perhaps it is necessary to change the stub of numbers.Real?

Regarding the second error:

running mypy --py2 # with 243 files
stdlib/2and3/fractions.pyi:3: error: No library stub file for standard library module 'decimal'
stdlib/2and3/fractions.pyi:3: note: (Stub files are from https://github.com/python/typeshed)

It is pretty obvious that the stub for the decimal module needs to be ported to python 2.
I would like to work on that. Should I start by moving decimal.pyi to the 2and3 directory?

matthiaskramm · 2016-02-26T17:00:19Z

Yes, that's a good place for it. The Python 2 and Python 3 versions don't seem to differ much. Feel free to just mark the Python 3 specific sections with comments. Once mypy has support for version conditionals we can do the proper

  if sys.version_info[0] == 3:
   ...

youtux · 2016-02-26T17:49:58Z

Feel free to just mark the Python 3 specific sections with comments. Once mypy has support for version conditionals we can do the proper
sys.version_info[0] == 3:
    ...

I don't quite get your comment. Do you mean that I should comment out the following code?

    if sys.version_info[0] >= 3:
        def floor(self) -> int: ...
        def ceil(self) -> int: ...

        @overload
        def __round__(self) -> int: ...

        @overload
        def __round__(self, ndigits: int) -> Fraction: ...

If that is the case, the stub would not be checked at all, am I wrong?

gvanrossum · 2016-02-26T18:18:46Z

Re: the signature of __round__: instead of using @overload, just use a default argument, i.e.

def __round__(self, ndigits: int = None): ...

Regarding the sys.version-info check, IIUC the proposal is to just leave out the if line and replace it with a comment saying soemthing like "TODO: this is for Python 3 only; fix when mypy supports sys.version_info checks"

gvanrossum · 2016-02-26T21:10:27Z

I've merged your decimal backport; can you rebase and clean up?

youtux · 2016-02-26T21:20:00Z

Yeah, just waiting for that.

youtux · 2016-02-26T21:33:21Z

Please, don't merge. There are missing properties of Fraction.

gvanrossum · 2016-02-26T21:37:51Z

OK, I'm waiting.

youtux · 2016-02-26T21:41:57Z

Should the stub also declare types for methods like __add__, __sub__, etc.? I suppose yes.

gvanrossum · 2016-02-26T21:49:43Z

Regarding __add__ etc., these signatures should really be inherited from Number. You can'y say e.g.

def __add__(self, other: Fraction) -> Fraction: ...

Because it actually supports other numbers too. So you'll have to write something like

def __add__(self, other: Number) -> Number: ...

This is unfortunate because it means that type-checking expressions involving Fractions is not very precise. We could add overloads but it would get pretty verbose... E.g.

@overload
def __add__(self, other: Union[Fraction, int]) -> Fraction: ...
@overload
def __add__(self, other: Number) -> Number: ...

but I'm not even sure if mypy currently support that -- please try it out with some real code. Thanks for bringing it up!

youtux · 2016-02-26T22:22:30Z

What about something like:

NumberType = TypeVar('T', Fraction, numbers.Real, numbers.Complex)

class Fraction(numbers.Rational):
    ...
    def __add__(self, other: NumberType) -> NumberType: ...

The rationale is that Fraction.__add__ seems to cast self to the upper category (float, complex) until they can be added.

gvanrossum · 2016-02-26T23:12:36Z

Yes, that sounds right!

youtux · 2016-02-27T00:13:16Z

I don't quite get why mypy complains.

gvanrossum · 2016-02-29T19:07:35Z

I think you're running into something that's unsupported currently by mypy.

@JukkaL can you shed your light on this issue? The key problem seems to be that the base class defines e.g.

def __add__(self, other: Number) -> Number: ...

and in a subclass we'd like to override this so that mypy understands that adding two Fractions returns a Fraction, but that adding a Fraction to a Number returns a Number (which is a superclass of Fraction).

Maybe also connected to #1237?

JukkaL · 2016-02-29T23:23:16Z

Hmm... mypy may be confused by the type variable in an operator method signature. Anyway, mypy is probably too eager in the overlapping check, as it guards against a pretty theoretical source of unsafety. I'll need to look into the code to figure out what's going on.

Other comments: Should UptoComplexT include Fraction as the first value?

youtux · 2016-03-01T00:09:32Z

Other comments: Should UptoComplexT include Fraction as the first value?

Probably yes, but I preferred to keep the numbers hierarchy (numbers.Rational, numbers.Real and numbers.Complex). I can insert Fraction as first value, too.

However, I think that the most accurate solution would be to have two types:

ForwardOpNumberT = TypeVar('ForwardOpNumberT', int, Fraction, float, complex)
ReverseOpNumberT = TypeVar('ReverseOpNumberT', numbers.Rational, numbers.Real, numbers.Complex)

for the forward and reverse operations like __add__, __radd__, __sub__, __rsub__, etc.

Should I just go with @overloads instead and spare the headache?

JukkaL · 2016-03-01T18:47:08Z

If @overload works, I'd recommend using it and maybe leaving a comment about potentially changing the code to use type variables in the future.

youtux · 2016-03-01T19:51:29Z

Tried with the following:

class Fraction(numbers.Rational):
    ...
    @overload
    def __add__(self, other: Union[int, Fraction]) -> Fraction: ...
    @overload
    def __add__(self, other: float) -> float: ...
    @overload
    def __add__(self, other: complex) -> complex: ...

    @overload
    def __radd__(self, other: numbers.Rational) -> Fraction: ...
    @overload
    def __radd__(self, other: numbers.Real) -> float: ...
    @overload
    def __radd__(self, other: numbers.Complex) -> complex: ...

Mypy still complains:

$ ./runtests.py -x tornado sqlalchemy 3/enum requests
running mypy  # with 207 files
stdlib/2and3/fractions.pyi: note: In class "Fraction":
stdlib/2and3/fractions.pyi:33: error: Signature of "__add__" incompatible with supertype "Complex"
stdlib/2and3/fractions.pyi: note: In member "__radd__" of class "Fraction":
stdlib/2and3/fractions.pyi:41: error: Signatures of "__radd__" of "Fraction" and "__add__" of "Rational" are unsafely overlapping
stdlib/2and3/fractions.pyi: note: In class "Fraction":
stdlib/2and3/fractions.pyi:41: error: Overloaded function signatures 1 and 2 overlap with incompatible return types
stdlib/2and3/fractions.pyi:41: error: Overloaded function signatures 1 and 3 overlap with incompatible return types
stdlib/2and3/fractions.pyi: note: In member "__radd__" of class "Fraction":
stdlib/2and3/fractions.pyi:43: error: Signatures of "__radd__" of "Fraction" and "__add__" of "Real" are unsafely overlapping
stdlib/2and3/fractions.pyi: note: In class "Fraction":
stdlib/2and3/fractions.pyi:43: error: Overloaded function signatures 2 and 2 overlap with incompatible return types
stdlib/2and3/fractions.pyi: note: In member "__radd__" of class "Fraction":
stdlib/2and3/fractions.pyi:45: error: Signatures of "__radd__" of "Fraction" and "__add__" of "Complex" are unsafely overlapping
[mypy --py2 omitted]

Therefore no, @overload does not work.

JukkaL · 2016-03-01T22:30:48Z

I looked in to this. This simplified fragment reproduces the issue:

from typing import TypeVar, Any

class Complex:
    def __add__(self, other): ...
    def __radd__(self, other): ...

class Rational(Complex):
    pass

UpToComplexT = TypeVar('UpToComplexT', Rational, Complex)

class Fraction(Rational):
    def __add__(self, other: UpToComplexT) -> UpToComplexT: ...
    def __radd__(self, other: UpToComplexT) -> UpToComplexT: ...

Mypy is complaining about this because the base classes don't have function annotations, though it perhaps shouldn't complain. However, simply adding annotations may not be sufficient. I'll see if I can give these reasonable types without generating errors.

gvanrossum · 2016-03-02T18:14:43Z

@JukkaL Is there a bug in the mypy tracker for this yet? If so could you link to it? If not could you create one? (I feel out of my depth here myself.)

JukkaL · 2016-03-02T18:18:35Z

Because of the current overlapping checks mypy probably can't represent this without giving errors. We'll probably have to make the overlapping checks more lenient, but I'm not sure what's the best way to do it yet. Operator overloading is a tricky area and requires careful thought. I'll create an issue for this in the mypy issue tracker.

JukkaL · 2016-03-02T18:29:25Z

Create issue python/mypy#1264.

gvanrossum · 2016-09-14T23:41:43Z

Closed in favor of #544. (@youtux, your attempts were not in vain! And feel free to help out improving the type signatures for #544.)

youtux mentioned this pull request Feb 26, 2016

Port decimal stub to Python 2 #95

Merged

fractions stub

44eff38

add many missing methods

e69cfe1

This was referenced Sep 14, 2016

Add partial stubs for fractions #544

Merged

[waiting for author] Add stubs for the statistics module #546

Closed

gvanrossum closed this Sep 15, 2016

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Stub for fractions #94

Stub for fractions #94

youtux commented Feb 26, 2016

youtux commented Feb 26, 2016

youtux commented Feb 26, 2016

matthiaskramm commented Feb 26, 2016

youtux commented Feb 26, 2016

gvanrossum commented Feb 26, 2016

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youtux commented Feb 26, 2016

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gvanrossum commented Sep 14, 2016

Stub for fractions #94

Stub for fractions #94

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youtux commented Feb 26, 2016

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