'Is it allowed to take derivative wrt to this instance.
This determines if it is allowed to take derivatives wrt this object.
Subclasses such as Symbol, Function and Derivative should return True
to enable derivatives wrt them. The implementation in Derivative
separates the Symbol and non-Symbol _diff_wrt=True variables and
temporarily converts the non-Symbol vars in Symbols when performing
the differentiation.
Note, see the docstring of Derivative for how this should work
mathematically. In particular, note that expr.subs(yourclass, Symbol)
should be well-defined on a structural level, or this will lead to
inconsistent results.
Examples
>>> from sympy import Expr
>>> e = Expr()
>>> e._diff_wrt
False
>>> class MyClass(Expr):
...     _diff_wrt = True
>>> (2*MyClass()).diff(MyClass())
2'

@property
def _diff_wrt(self):

    return False
