Module: sage.misc.sage_eval
Module-level Functions
_obj_, [extra_locals=]) |
Obtain a SAGE object from the input string by evaluate it using SAGE (including preparsing and in the context of the SAGE library, etc.).
All preparsing is applied and the expression is evaluated in the
context of from sage.all import *
. To evaluate the
expression with certain variables set, use the extra_locals
argument, which should be a dictionary.
This example illustrates that preparsing is applied.
sage: eval('2^3') 1 sage: sage_eval('2^3') 8
This illustrates interfaces:
sage: f = gp('x^3 + x + 1') sage: f._sage_() x^3 + x + 1 sage: type(f._sage_()) <class 'sage.rings.polynomial_element.Polynomial_rational_dense'> sage: a = gap(939393/2433) sage: a._sage_() 313131/811 sage: type(a._sage_()) <type 'rational.Rational'>
This example illustrates that evaluation occurs in the context of
from sage.all import *
. Even though bernoulli has been
redefined in the local scope, when calling sage_eval
the
default value meaning of bernoulli is used. Likewise for QQ
below.
sage: bernoulli = lambda x : x^2 sage: bernoulli(6) 36 sage: eval('bernoulli(6)') 36 sage: sage_eval('bernoulli(6)') 1/42
sage: QQ = lambda x : x^2 sage: QQ(2) 4 sage: sage_eval('QQ(2)') 2 sage: parent(sage_eval('QQ(2)')) Rational Field
This example illustrates setting a variable for use in evaluation.
sage: x = 5 sage: eval('4/3 + x', {'x':25}) 26 sage: sage_eval('4/3 + x', {'x':25}) 79/3
This example illustrates how sage_eval
can be useful
when evaluating the output of other computer algebra systems.
sage: x = PolynomialRing(Q).gen() sage: gap.eval('R:=PolynomialRing(Rationals,["x"]);') 'PolynomialRing(..., [ x ])' sage: ff = gap.eval('x:=IndeterminatesOfPolynomialRing(R);; f:=x^2+1;') sage: ff; sage_eval(ff) 'x^2+1' x^2 + 1 sage: eval(ff) Traceback (most recent call last): ... RuntimeError: Use ** for exponentiation, not '^', which means xor in Python, and has the wrong precedence.
Here you can see eval simply will not work but sage_eval
will.
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