tsolve rewriting as exp

[ethankward]

sympy/sympy/solvers/solvers.py

Lines 2768 to 2769 in a29cb79

	rewrite = lhs.rewrite(exp)
	if rewrite != lhs:

These lines can cause problems if lhs doesn't have an explicit exp rewriting method, for example:

>>> e = zeta(x**pi, 8)
>>> solve(e, x)
Traceback (most recent call last):
  File "test.py", line 46, in <module>
    print(solve(e, x))
  File "/home/eward/se/sympy/solvers/solvers.py", line 1171, in solve
    solution = _solve(f[0], *symbols, **flags)
  File "/home/eward/se/sympy/solvers/solvers.py", line 1686, in _solve
    iv = _solve(u - t, symbol, **flags)
  File "/home/eward/se/sympy/solvers/solvers.py", line 1737, in _solve
    soln = _tsolve(f_num, symbol, **flags)
  File "/home/eward/se/sympy/solvers/solvers.py", line 2770, in _tsolve
    return _solve(rewrite - rhs, sym, **flags)
  File "/home/eward/se/sympy/solvers/solvers.py", line 1686, in _solve
    iv = _solve(u - t, symbol, **flags)
...
    return _solve(rewrite - rhs, sym, **flags)
  File "/home/eward/se/sympy/solvers/solvers.py", line 1508, in _solve
    f_num, sol = solve_linear(f, symbols=symbols)
  File "/home/eward/se/sympy/solvers/solvers.py", line 2124, in solve_linear
    dnewn_dxi = newn.diff(xi)
  File "/home/eward/se/sympy/core/expr.py", line 3424, in diff
    return Derivative(self, *symbols, **assumptions)
  File "/home/eward/se/sympy/core/function.py", line 1416, in __new__
    obj = expr._eval_derivative_n_times(v, count)
  File "/home/eward/se/sympy/core/basic.py", line 1743, in _eval_derivative_n_times
    obj2 = obj._accept_eval_derivative(s)
  File "/home/eward/se/sympy/core/basic.py", line 1719, in _accept_eval_derivative
    return s._visit_eval_derivative_scalar(self)
  File "/home/eward/se/sympy/core/basic.py", line 1724, in _visit_eval_derivative_scalar
    return base._eval_derivative(self)
  File "/home/eward/se/sympy/core/cache.py", line 94, in wrapper
    retval = cfunc(*args, **kwargs)
  File "/home/eward/se/sympy/core/add.py", line 404, in _eval_derivative
    return self.func(*[a.diff(s) for a in self.args])
  File "/home/eward/se/sympy/core/add.py", line 404, in <listcomp>
    return self.func(*[a.diff(s) for a in self.args])
  File "/home/eward/se/sympy/core/expr.py", line 3424, in diff
    return Derivative(self, *symbols, **assumptions)
  File "/home/eward/se/sympy/core/function.py", line 1416, in __new__
    obj = expr._eval_derivative_n_times(v, count)
  File "/home/eward/se/sympy/core/basic.py", line 1743, in _eval_derivative_n_times
    obj2 = obj._accept_eval_derivative(s)
  File "/home/eward/se/sympy/core/basic.py", line 1719, in _accept_eval_derivative
    return s._visit_eval_derivative_scalar(self)
  File "/home/eward/se/sympy/core/basic.py", line 1724, in _visit_eval_derivative_scalar
    return base._eval_derivative(self)
  File "/home/eward/se/sympy/core/function.py", line 607, in _eval_derivative
    l.append(df * da)
  File "/home/eward/se/sympy/core/decorators.py", line 91, in __sympifyit_wrapper
    return func(a, b)
  File "/home/eward/se/sympy/core/decorators.py", line 129, in binary_op_wrapper
    return func(self, other)
  File "/home/eward/se/sympy/core/expr.py", line 196, in __mul__
    return Mul(self, other)
  File "/home/eward/se/sympy/core/cache.py", line 94, in wrapper
    retval = cfunc(*args, **kwargs)
  File "/home/eward/se/sympy/core/function.py", line 2209, in __eq__
    return self._hashable_content() == other._hashable_content()
  File "/home/eward/se/sympy/core/function.py", line 2220, in _hashable_content
    zip(self.variables, self.point) if not self.expr.has(v)]))
  File "/home/eward/se/sympy/core/function.py", line 2220, in <listcomp>
    zip(self.variables, self.point) if not self.expr.has(v)]))
  File "/home/eward/se/sympy/core/cache.py", line 94, in wrapper
    retval = cfunc(*args, **kwargs)
  File "/home/eward/se/sympy/core/expr.py", line 134, in __eq__
    if a != b:
  File "/home/eward/se/sympy/core/containers.py", line 97, in __eq__
    return super(Tuple, self).__eq__(other)
  File "/home/eward/se/sympy/core/basic.py", line 343, in __eq__
    return self._hashable_content() == other._hashable_content()
  File "/home/eward/se/sympy/core/expr.py", line 133, in __eq__
    a, b = self._hashable_content(), other._hashable_content()
  File "/home/eward/se/sympy/core/symbol.py", line 381, in _hashable_content
    return Symbol._hashable_content(self) + (self.dummy_index,)
  File "/home/eward/se/sympy/core/symbol.py", line 274, in _hashable_content
    return (self.name,) + tuple(sorted(self.assumptions0.items()))
  File "/home/eward/se/sympy/core/symbol.py", line 284, in assumptions0
    in self._assumptions.items() if value is not None)
RecursionError: maximum recursion depth exceeded

The inner power gets rewritten as exp(pi*log(x)) but when solve is called it will get changed back again. In some cases like sinc where there is a rewriting it's possible to work around this (#17520), but not for zeta.