Dear all,
from the method-name and also from the one-line description
"Return True if this symbolic expression is a constant."
of Expression.is_constant, I expected that this gives more or less the
same result as checking whether symbolic expression has an empty
.variables(). However, we have
sage: log(2).is_constant()
False
and also
sage: SR(2).is_constant()
False
only pi, e and that stuff is "constant".
I find this very confusing. Am I alone with this feeling?
The above is also inconsistent to
sage: P.<p> = ZZ[]
sage: P(2).is_constant()
True
Best wishes,
Daniel
PS: To be fair, after the one-line description, it is explained what it
really does:
This function is intended to provide an interface to query the
internal representation of the expression. In this sense, the word
"constant" does not reflect the mathematical properties of the
expression. Expressions which have no variables may return "False".
But the phrase "the internal representation of the expression" sounds
like the end user should not care about it... (i.e. this is_constant
could be an underscore-method...).
PPS: At the moment (not having answers to this posting), my favourite
implementation would be something like
def is_constant(self):
return not self.variables()
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