`expand_power_exp()` Has No Effect In Cases For Which It Should about sympy

[smichr]

The docstring of expand_power_exp also indicates

    >>> expand_power_exp(x**(y + 2))
    x**(y + 2)

    If ``x = 0`` the value of the expression depends on the
    value of ``y``; if the expression were expanded the result
    would be 0. So expansion is only done if ``x != 0``:

    >>> expand_power_exp(Symbol('x', zero=False)**(y + 2))
    x**2*x**y

Since we don't know if the base is zero or not we don't do the expansion. But if we know x is not zero then it is ok:

>>> a, b = symbols("a, b", complex=True)
>>> x = var('x', zero=False)
>>> expand_power_exp(x**(a+b))
x**a*x**b

[ricopicone]

It seems that $x > 0$ is the key:

a, b = sp.symbols("a, b", complex=True)
x = sp.symbols("x", positive=True)
sp.expand_power_exp(x**(a + b))

[ricopicone]

Ah, excellent. Thank you @smichr!