def __init__(self, subject):
        self._subject = subject
Returns all the variable names found in the expression.
dataset/ETHPy150Open kayhayen/Nuitka/nuitka/build/inline_copy/lib/scons-2.3.2/SCons/Util.py/Proxy.__init__--crossover with--dataset/ETHPy150Open bzimmer/pysmug/pysmug/smugfind.py/Predicate.names