VarRenamer Bugs

[MrBlack0220]

Hi，thanks for the amazing work!
When I try to rename variable name with recode-main/natgen/transformations/var_renaming_transformation.py，I find when extracting variable name，some function name can be extracted even after flitterng withget_not_var_ptype_var_names(self, root, code_string) method:
python code = """
a = input()
l = []
l.append(a)
b = " ".join(l)
"""
var_names = ['a', 'join', 'l', 'b', 'append']
Function name append and join will be extracted.
Someting wrong here?