Questions about how frac, numer, denom flags work with expand

[sylee957]

I have investigated how frac, numer, denom flags are defined to work for polynomial expressions.

>>> from sympy import *
>>> w, x, y, z = symbols('w x y z')
>>> a, b, c, d = symbols('a b c d')
>>> expr = (a + b)*(c + d)/(w + x)/(y + z)
>>> expr.expand(frac=False, numer=False, denom=False)
a*c/(w*y + w*z + x*y + x*z) + a*d/(w*y + w*z + x*y + x*z) + b*c/(w*y + w*z + x*y + x*z) + b*d/(w*y + w*z + x*y + x*z)
>>> expr.expand(frac=True, numer=False, denom=False)
(a*c + a*d + b*c + b*d)/(w*y + w*z + x*y + x*z)
>>> expr.expand(frac=False, numer=True, denom=False)
(a*c + a*d + b*c + b*d)/((w + x)*(y + z))
>>> expr.expand(frac=False, numer=False, denom=True)
(a + b)*(c + d)/(w*y + w*z + x*y + x*z)

But I also notice that things are not working consistently if the expression is not a single rational expression, but an addition of rational expressions.

>>> expr = (a + b)/(w + x)/(y + z) + (c + d)/(w + x)/(y + z)
>>> expr.expand(frac=False, numer=False, denom=False)
a/(w*y + w*z + x*y + x*z) + b/(w*y + w*z + x*y + x*z) + c/(w*y + w*z + x*y + x*z) + d/(w*y + w*z + x*y + x*z)
>>> expr.expand(frac=True, numer=False, denom=False)
a/(w*y + w*z + x*y + x*z) + b/(w*y + w*z + x*y + x*z) + c/(w*y + w*z + x*y + x*z) + d/(w*y + w*z + x*y + x*z)
>>> expr.expand(frac=False, numer=True, denom=False)
a/(w*y + w*z + x*y + x*z) + b/(w*y + w*z + x*y + x*z) + c/(w*y + w*z + x*y + x*z) + d/(w*y + w*z + x*y + x*z)
>>> expr.expand(frac=False, numer=False, denom=True)
(a + b)/((w + x)*(y + z)) + (c + d)/((w + x)*(y + z))

Because 1,2,3 results are actually expanding the denominator even if denom=False, and fourth result is not expanding the denominator even if denom=True

And I wonder the above results are issue and should be handled like

// expand with denom=True
(a + b)/(w + x)/(y + z) + (c + d)/(w + x)/(y + z) => 
(a + b)/(w*y + w*z + x*y + x*z) + (c + d)/(w + x)/(w*y + w*z + x*y + x*z)

// expand with numer=True
(a + b)*(c + d)/(w + x) + (e + f)*(g + h)/(w + x) => 
(a*c + a*d + b*c + b*d)/(w + x) + (e*g + e*h + f*g + f*h)/(w + x)

// expand with frac=True
(a + b)*(c + d)/(w + x)/(y + z) + (e + f)*(g + h)/(w + x)/(y + z) => 
(a*c + a*d + b*c + b*d)/(w*y + w*z + x*y + x*z) + (e*g + e*h + f*g + f*h)/(w*y + w*z + x*y + x*z)