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 instance sympy.Q.

sympy.assumptions.ask.ask(proposition, assumptions=True, context={})[source]¶

Function to evaluate the proposition with assumptions.

Parameters:

proposition : Boolean

Proposition which will be evaluated to boolean value. If this is not AppliedPredicate, it will be wrapped by Q.is_true.

assumptions : Boolean, 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, or None

Raises:

TypeError : proposition or assumptions is not valid logical expression.

ValueError : assumptions are inconsistent.

Explanation

This function evaluates the proposition to True or False if the truth value can be determined. If not, it returns None.

It should be discerned from refine() which, when applied to a proposition, simplifies the argument to symbolic Boolean instead of Python built-in True, False or None.

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.