expression conversion bug with Sympy functions

[rwst]

With the Sympy-1.0 upgrade (#20185)

sage: import sympy
sage: u = sympy.Function('u'); n = sympy.Symbol('n', integer=True)
sage: sympy.sympify(3*u(n), evaluate=False)
/home/ralf/sage/local/lib/python2.7/site-packages/sympy-1.0-py2.7.egg/sympy/parsing/sympy_parser.pyc in flatten(self, args, func)
    922         result = []
    923         for arg in args:
--> 924             if isinstance(arg, ast.Call) and arg.func.id == func:
    925                 result.extend(self.flatten(arg.args, func))
    926             else:

AttributeError: 'Call' object has no attribute 'id'

which disappears when 3*u(n) is changed to u(n)*3 or u(n)

Reported as sympy/sympy#10795

Component: symbolics

Issue created by migration from https://trac.sagemath.org/ticket/20194

[rwst]

Upstream: Reported upstream. No feedback yet.

[rwst]

comment:3

This was resolved in #20185.

[rwst]

Changed upstream from Reported upstream. No feedback yet. to none