On Fri, Jul 22, 2022 at 10:51 AM Anton Makarov <[email protected]> wrote:
>
> Hi, I am new to sympy. I am trying to understand what is the best practice to
> check head of expression? For example:
> expr = sympify("somefunc(1-x)")
> Is this a best practice or there is a better way to do this?
Undefined functions created from sympify will have the
UndefinedFunction metaclass, which you can test directly with
>>> from sympy.core.function import UndefinedFunction
>>> isinstance(sympify("somefunc(1-x)").func, UndefinedFunction)
True
>>> sympify("somefunc(1-x)").func.name == 'somefunc'
True
Or alternately you can just check
>>> sympify("somefunc(1-x)").func == Function('somefunc')
True
Note that this won't apply to functions that are predefined in SymPy like sin().
> How to understand that head of expr is somefunc? I can do it like this:
> if str(expr.func) == "somefunc"
> And by the way, if I have the expression:
> expr = sympify("x")
> How can I check that expr is some variable (not necessary "x", but in more
> broader sense)?
isinstance(expr, Symbol)
> Or:
> expr = sympify("5.5777")
> how to check that expr is some number?
isinstance(expr, Number)
Aaron Meurer
>
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