Simplify `expr` assuming `x` is positive.

simplify_with_pos.py

import sympy


def recfactor(expr, deep=False):
    """Recursively factorize `expr` including additive terms."""
    if isinstance(expr, (sympy.Mul, sympy.Add)):
        cls = type(expr)
        return cls(*[
            recfactor(a, deep=deep).factor(deep=deep)
            for a in expr.args
        ])
    else:
        return expr


def simplify_with_pos(expr, x,
                      f=lambda e: recfactor(e.expand().cancel()).simplify()):
    """Simplify `expr` assuming `x` is positive."""
    y = sympy.Dummy(positive=True)
    return f(expr.subs(x, y)).subs(y, x)