[Python] How can I get a list of the symbols in a SymPy expression?

For example, if I run

import sympy
x, y, z = sympy.symbols('x:z')
f = sympy.exp(x + y) - sympy.sqrt(z)


is there any method of f that I can use to get a list or tuple of sympy.Symbol objects that the expression contains? I'd rather not have to parse srepr(f) or parse downward through f.args.

In this case, g.args[0].args[1].args[0] gives me Symbol("z"), while g.args[1].args[0].args gives me the tuple (Symbol("x"), Symbol("y")), but obviously these are expression-specific.

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