Coverage for local/lib/python2.7/site-packages/sage/misc/inherit_comparison.pyx : 71%

""" 

Metaclass for inheriting comparison functions 

This module defines a metaclass :class:`InheritComparisonMetaclass` to 

inherit comparison functions in Cython extension types. In Python 2, 

the special methods ``__richcmp__``, ``__cmp__`` and ``__hash__`` are 

only inherited as a whole: defining just 1 or 2 of these will prevent 

the others from being inherited. 

To solve this issue, you can use :class:`InheritComparisonMetaclass` 

as a Cython "metaclass" (see :mod:`sage.cpython.cython_metaclass` for the 

general mechanism). If you do this for an extension type which defines 

neither ``__richcmp__`` nor ``__cmp__``, then both these methods are 

inherited from the base class (the MRO is not used). 

In Sage, this is in particular used for 

:class:`sage.structure.element.Element` to support comparisons using 

the coercion framework. 

None of this is relevant to Python classes, which inherit comparison 

methods anyway. 

AUTHOR: 

- Jeroen Demeyer (2015-05-22): initial version, see :trac:`18329` 

""" 

#***************************************************************************** 

# Copyright (C) 2015 Jeroen Demeyer <jdemeyer@cage.ugent.be> 

# 

# This program is free software: you can redistribute it and/or modify 

# it under the terms of the GNU General Public License as published by 

# the Free Software Foundation, either version 2 of the License, or 

# (at your option) any later version. 

# http://www.gnu.org/licenses/ 

#***************************************************************************** 

from cpython.object cimport PyTypeObject 

from sage.misc.classcall_metaclass cimport ClasscallMetaclass 

cdef extern from "inherit_comparison_impl.c": 

void inherit_comparison(PyTypeObject* dst, PyTypeObject* src) 

cdef class InheritComparisonMetaclass(type): 

""" 

If the type does not define ``__richcmp__`` nor ``__cmp__``, 

inherit both these methods from the base class. The difference with 

plain extension types is that comparison is inherited even if 

``__hash__`` is defined. 

EXAMPLES:: 

sage: cython(''' 

....: from sage.misc.inherit_comparison cimport InheritComparisonMetaclass 

....: 

....: cdef class Base(object): 

....: def __richcmp__(left, right, int op): 

....: print("Calling Base.__richcmp__") 

....: return left is right 

....: 

....: cdef class Derived(Base): 

....: def __hash__(self): 

....: return 1 

....: 

....: cdef class DerivedWithRichcmp(Base): 

....: def __getmetaclass__(_): 

....: from sage.misc.inherit_comparison import InheritComparisonMetaclass 

....: return InheritComparisonMetaclass 

....: def __hash__(self): 

....: return 1 

....: ''') 

sage: a = Derived() 

sage: a == a 

True 

sage: b = DerivedWithRichcmp() 

sage: b == b 

Calling Base.__richcmp__ 

True 

""" 

def __init__(self, *args): 

cdef PyTypeObject* t = <PyTypeObject*>self 

cdef PyTypeObject* b = t.tp_base 

if b: 

inherit_comparison(t, b) 

super(InheritComparisonMetaclass, self).__init__(*args) 

class InheritComparisonClasscallMetaclass(ClasscallMetaclass, InheritComparisonMetaclass): 

""" 

Combine :class:`ClasscallMetaclass` with 

:class:`InheritComparisonMetaclass`. 

TESTS:: 

sage: from sage.misc.inherit_comparison import InheritComparisonClasscallMetaclass as M 

sage: M.__new__(M, "myclass", (object,), {}) 

<class '__main__.myclass'> 

"""