Coverage for local/lib/python2.7/site-packages/sage/misc/unknown.py : 48%

""" 

The Unknown truth value 

AUTHORS: 

- Florent Hivert (2010): initial version. 

""" 

from __future__ import print_function 

from sage.structure.sage_object import SageObject 

from sage.structure.unique_representation import UniqueRepresentation 

from sage.structure.richcmp import richcmp_method, rich_to_bool 

@richcmp_method 

class UnknownClass(UniqueRepresentation, SageObject): 

""" 

TESTS:: 

sage: TestSuite(Unknown).run() 

""" 

def __init__(self): 

""" 

The ``Unknown`` truth value 

EXAMPLES:: 

sage: l = [False, Unknown, True] 

sage: for a in l: print([a and b for b in l]) 

[False, False, False] 

[Unknown, Unknown, Unknown] 

[False, Unknown, True] 

sage: for a in l: print([a or b for b in l]) 

[False, Unknown, True] 

[False, Unknown, True] 

[True, True, True] 

.. WARNING:: 

Unless PEP 335 is accepted, in the following cases, 

``and``, ``not`` and ``or`` return a somewhat wrong value:: 

sage: not Unknown # should return Unknown 

True 

sage: Unknown and False # should return False 

Unknown 

sage: Unknown or False # should return Unknown 

False 

""" 

def _repr_(self): 

""" 

TESTS:: 

sage: Unknown 

Unknown 

""" 

return "Unknown" 

def __bool__(self): 

""" 

When evaluated in a boolean context ``Unknown()`` is evaluated into 

``False``. 

EXAMPLES:: 

sage: bool(Unknown) 

False 

sage: not Unknown 

True 

""" 

return False 

__nonzero__ = __bool__ 

def __and__(self, other): 

""" 

The ``and`` logical connector. 

.. WARNING:: 

This is not used by ``and`` unless PEP 335 is accepted. 

EXAMPLES:: 

sage: Unknown & False 

False 

sage: Unknown & Unknown 

Unknown 

sage: Unknown & True 

Unknown 

Compare with:: 

sage: Unknown and False # should return False 

Unknown 

""" 

if other is False: 

return False 

else: 

return self 

def __or__(self, other): 

""" 

The ``or`` logical connector. 

.. WARNING:: 

This is not used by ``or`` unless PEP 335 is accepted. 

EXAMPLES:: 

sage: Unknown | False 

Unknown 

sage: Unknown | Unknown 

Unknown 

sage: Unknown | True 

True 

Compare with:: 

sage: Unknown or False # should return Unknown 

False 

""" 

if other: 

return True 

else: 

return self 

def __not__(self): 

""" 

The ``not`` logical connector. 

.. WARNING:: 

This is not used by ``not`` unless PEP 335 is accepted. 

EXAMPLES:: 

sage: Unknown.__not__() 

Unknown 

Compare with:: 

sage: not Unknown # should return Unknown 

True 

""" 

return self 

def __richcmp__(self, other, op): 

""" 

Comparison of truth value. 

EXAMPLES:: 

sage: l = [False, Unknown, True] 

sage: for a in l: print([a < b for b in l]) 

[False, True, True] 

[False, False, True] 

[False, False, False] 

sage: for a in l: print([a <= b for b in l]) 

[True, True, True] 

[False, True, True] 

[False, False, True] 

""" 

if other is self: 

return rich_to_bool(op, 0) 

if not isinstance(other, bool): 

return NotImplemented 

if other: 

return rich_to_bool(op, -1) 

else: 

return rich_to_bool(op, +1) 

Unknown = UnknownClass()