algebra.py 文件源码

def _findVars(x, res):
    """
    Find all variables in a tree
    """
    if isinstance(x, Variable):
        res.add(x)
    if isinstance(x, CompValue):
        if x.name == "Bind":
            res.add(x.var)
            return x  # stop recursion and finding vars in the expr
        elif x.name == 'SubSelect':
            if x.projection:
                res.update(v.var or v.evar for v in x.projection)
            return x