Miscellaneous utilities

class sage.structure.misc.A

Bases: object

class sage.structure.misc.AttributeErrorMessage

Bases: object

Tries to emulate the standard Python AttributeError message.

Note

The typical fate of an attribute error is being caught. Hence, under normal circumstances, nobody will ever see the error message. The idea for this class is to provide an object that is fast to create and whose string representation is an attribute error’s message. That string representation is only created if someone wants to see it.

EXAMPLES:

sage: 1.bla  #indirect doctest
Traceback (most recent call last):
...
AttributeError: 'sage.rings.integer.Integer' object has no attribute 'bla'
sage: QQ[x].gen().bla
Traceback (most recent call last):
...
AttributeError: 'sage.rings.polynomial.polynomial_rational_flint.Polynomial_rational_flint' object has no attribute 'bla'
sage: from sage.structure.misc import AttributeErrorMessage
sage: AttributeErrorMessage(int(1),'bla')
'int' object has no attribute 'bla'

TESTS:

By trac ticket #14100, the attribute errors raised on elements and parents are unique objects. The error message of this unique error object is changed inplace. This is for reasons of efficiency.

sage: try:
....:     1.__bla
....: except AttributeError as ElementError:
....:     pass
sage: ElementError
AttributeError('sage.rings.integer.Integer' object has no attribute '__bla',)
sage: try:
....:     x.__bla
....: except AttributeError as ElementError2:
....:     pass
sage: ElementError2 is ElementError
True
sage: ElementError
AttributeError('sage.symbolic.expression.Expression' object has no attribute '__bla',)
sage: isinstance(ElementError.message, sage.structure.misc.AttributeErrorMessage)
True

Hence, if one really needs the error message as a string, then one should make a copy of its string representation before it changes. Attribute Errors of parents behave similarly:

sage: try:
....:     QQ.__bla
....: except AttributeError as ParentError:
....:     pass
sage: ParentError
AttributeError('RationalField_with_category' object has no attribute '__bla',)
sage: try:
....:     ZZ.__bla
....: except AttributeError as ParentError2:
....:     pass
sage: ParentError2 is ParentError
True
sage: ParentError2
AttributeError('sage.rings.integer_ring.IntegerRing_class' object has no attribute '__bla',)
sage: ParentError2 is ElementError
False

AUTHOR:

• Simon King (2011-05-21)

cls

name

sage.structure.misc.dir_with_other_class(self, cls)

Emulates dir(self), as if self was also an instance cls, right after caller_class in the method resolution order (self.__class__.mro())

EXAMPLES:

sage: class A(object):
...      a = 1
...      b = 2
...      c = 3
sage: class B(object):
...      b = 2
...      c = 3
...      d = 4
sage: x = A()
sage: x.c = 1; x.e = 1
sage: sage.structure.parent.dir_with_other_class(x, B)
[..., 'a', 'b', 'c', 'd', 'e']

Check that objects without dicts are well handled:

sage: cython("cdef class A:\n    cdef public int a")
sage: cython("cdef class B:\n    cdef public int b")
sage: x = A()
sage: x.a = 1
sage: hasattr(x,'__dict__')
False
sage: sage.structure.parent.dir_with_other_class(x, B)
[..., 'a', 'b']

TESTS:

Check that #13043 is fixed:

sage: len(dir(RIF))==len(set(dir(RIF)))
True

sage.structure.misc.getattr_from_other_class(self, cls, name)

INPUT:

- ``self``: some object
- ``cls``: a class
- ``name``: a string

Emulates getattr(self, name), as if self was an instance of cls.

If self is an instance of cls, raises an AttributeError, to avoid a double lookup. This function is intended to be called from __getattr__, and so should not be called if name is an attribute of self.

TODO: lookup if such a function readilly exists in Python, and if not triple check this specs and make this implementation rock-solid.

Caveat: this is pretty hacky, does not handle caching, there is no guarantee of robustness with super calls and descriptors, ...

EXAMPLES:

sage: from sage.structure.parent import getattr_from_other_class
sage: class A(object):
...        def inc(self):
...            return self + 1
...        @lazy_attribute
...        def lazy_attribute(self):
...            return repr(self)
sage: getattr_from_other_class(1, A, "inc")
<bound method A.inc of 1>
sage: getattr_from_other_class(1, A, "inc")()
2

Caveat: lazy attributes work with extension types only if they allow attribute assignment or have a public attribute __cached_methods of type <dict>. This condition is satisfied, e.g., by any class that is derived from Parent:

sage: getattr_from_other_class(1, A, "lazy_attribute")
Traceback (most recent call last):
...
AttributeError: 'sage.rings.integer.Integer' object has no attribute 'lazy_attribute'

The integer ring is a parent, so, lazy attributes work:

sage: getattr_from_other_class(ZZ, A, "lazy_attribute")
'Integer Ring'
sage: getattr_from_other_class(PolynomialRing(QQ, name='x', sparse=True).one(), A, "lazy_attribute")
'1'
sage: getattr_from_other_class(PolynomialRing(QQ, name='x', implementation="FLINT").one(), A, "lazy_attribute")
Traceback (most recent call last):
...
AttributeError: 'sage.rings.polynomial.polynomial_rational_flint.Polynomial_rational_flint'
object has no attribute 'lazy_attribute'

In general, descriptors are not yet well supported, because they often do not accept to be cheated with the type of their instance:

sage: A.__weakref__.__get__(1)
Traceback (most recent call last):
...
TypeError: descriptor '__weakref__' for 'A' objects doesn't apply
to 'sage.rings.integer.Integer' object

When this occurs, an AttributeError is raised:

sage: getattr_from_other_class(1, A, "__weakref__")
Traceback (most recent call last):
...
AttributeError: 'sage.rings.integer.Integer' object has no attribute '__weakref__'

This was caught by #8296 for which we do a couple more tests:

sage: "__weakref__" in dir(A)
True
sage: "__weakref__" in dir(1)
True
sage: 1.__weakref__
Traceback (most recent call last):
...
AttributeError: 'sage.rings.integer.Integer' object has no attribute '__weakref__'

sage: n = 1
sage: ip = get_ipython()                 # not tested: only works in interactive shell
sage: ip.magic_psearch('n.N')            # not tested: only works in interactive shell
n.N
sage: ip.magic_psearch('n.__weakref__')  # not tested: only works in interactive shell

Caveat: When __call__ is not defined for instances, using A.__call__ yields the method __call__ of the class. We use a workaround but there is no guarantee for robustness.

sage: getattr_from_other_class(1, A, “__call__”) Traceback (most recent call last): ... AttributeError: ‘sage.rings.integer.Integer’ object has no attribute ‘__call__’

sage.structure.misc.is_extension_type(cls)

INPUT:

• cls: a class

Tests whether cls is an extension type (int, list, cython compiled classes, ...)

EXAMPLES:

sage: from sage.structure.parent import is_extension_type
sage: is_extension_type(int)
True
sage: is_extension_type(list)
True
sage: is_extension_type(ZZ.__class__)
True
sage: is_extension_type(QQ.__class__)
False