Ask¶
Module for querying SymPy objects about assumptions.
- class sympy.assumptions.ask.AssumptionKeys[source]¶
This class contains all the supported keys by
ask
. It should be accessed via the instancesympy.Q
.
- sympy.assumptions.ask.ask(proposition, assumptions=True, context={})[source]¶
Function to evaluate the proposition with assumptions.
- Parameters
proposition : Any boolean expression.
Proposition which will be evaluated to boolean value. If this is not
AppliedPredicate
, it will be wrapped byQ.is_true
.assumptions : Any boolean expression, optional.
Local assumptions to evaluate the proposition.
context : AssumptionsContext, optional.
Default assumptions to evaluate the proposition. By default, this is
sympy.assumptions.global_assumptions
variable.- Returns
True
,False
, orNone
- Raises
TypeError : proposition or assumptions is not valid logical expression.
ValueError : assumptions are inconsistent.
Explanation
This function evaluates the proposition to
True
orFalse
if the truth value can be determined. If not, it returnsNone
.It should be discerned from
refine()
which, when applied to a proposition, simplifies the argument to symbolicBoolean
instead of Python built-inTrue
,False
orNone
.Syntax
- ask(proposition)
Evaluate the proposition in global assumption context.
- ask(proposition, assumptions)
Evaluate the proposition with respect to assumptions in global assumption context.
Examples
>>> from sympy import ask, Q, pi >>> from sympy.abc import x, y >>> ask(Q.rational(pi)) False >>> ask(Q.even(x*y), Q.even(x) & Q.integer(y)) True >>> ask(Q.prime(4*x), Q.integer(x)) False
If the truth value cannot be determined,
None
will be returned.>>> print(ask(Q.odd(3*x))) # cannot determine unless we know x None
ValueError
is raised if assumptions are inconsistent.>>> ask(Q.integer(x), Q.even(x) & Q.odd(x)) Traceback (most recent call last): ... ValueError: inconsistent assumptions Q.even(x) & Q.odd(x)
Notes
Relations in assumptions are not implemented (yet), so the following will not give a meaningful result.
>>> ask(Q.positive(x), x > 0)
It is however a work in progress.
See also
sympy.assumptions.refine.refine
Simplification using assumptions. Proposition is not reduced to
None
if the truth value cannot be determined.