How to get actual user defined variable name in Python Abstract Syntax Tree (AST)?

Question

From the given code snippet below, I tried to extract the actual user defined variable name other than the python built-in variable in order to check them agaist my naming convention rules.

ast_example.py

import ast
from pprint import pprint


def main():
    FirstName = "Johnny"
    LastName = "David"
    Variable_One = "Variable1"
    Variable_Two = "Variable2"
    Variable_Three = "Variable3"
    with open("ast_example.py", "r") as source:
        tree = ast.parse(source.read())

    analyzer = Analyzer()
    analyzer.visit(tree)
    analyzer.report()


class Analyzer(ast.NodeVisitor):
    def __init__(self):
        self.stats = {"variable": []}

    def visit_Name(self, node):
        print "Node: ",node.id
        self.stats["variable"].append(node.id)
        self.generic_visit(node)

    def report(self):
        pprint(self.stats)


if __name__ == "__main__":
    main()

However, after I executed the above code snippet, it resulted in not only the variables I wanted but also every python built in variables as well such as self, __name__, open, source, etc which are those I want to exclude.

{'variable': ['FirstName',
              'LastName',
              'Variable_One',
              'Variable_Two',
              'Variable_Three',
              'open',
              'source',
              'tree',
              'ast',
              'source',
              'analyzer',
              'Analyzer',
              'analyzer',
              'tree',
              'analyzer',
              'ast',
              'self',
              'self',
              'self',
              'node',
              'self',
              'node',
              'self',
              'node',
              'self',
              'pprint',
              'self',
              '__name__',
              'main']}

How can I exclude those built in variables? Thanks

None of self, __name__, open, source are keywords. They're variable names. The keywords here are import, from, def, with, as, class, print and if - and none of them are included in your list, as expected. — ForceBru
– ForceBru, Commented Jan 20, 2020 at 10:18
@ForceBru, ah sorry and thank you for your feedback. I have updated my question to match with that already. I want to exclude those built in from my result list. Thanks — Houy Narun
– Houy Narun, Commented Jan 20, 2020 at 10:26

BlueSheepToken · Accepted Answer · 2020-01-20 10:45:31Z

2

Instead of visiting Name you might want to visist Assign which is the node that represents assignement.

So the code looks something like this :

def visit_Assign(self, node):
    for target in node.targets:
        self.stats["variable"].append(target.id)
    self.generic_visit(node)

Here targets, represents the multiple values for assignement such as : a, b = 0, 1

ref: python ast doc

answered Jan 20, 2020 at 10:45

BlueSheepToken

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3 Comments

Houy Narun Over a year ago

Thanks, but I got a strange exception AttributeError: 'Attribute' object has no attribute 'id'. Indeed, by printing target.__dict__ it returned {'ctx': <_ast.Store object at 0x7f699c4d0f90>, 'id': 'FirstName', 'col_offset': 4, 'lineno': 6}, but could not access attrib id even though via ` target.get('id')`. Thanks

Houy Narun Over a year ago

I found an error. That was because the last object of target did not contain attrib id. To resolve this, I used try/except, and it worked. Thanks so much :)

BlueSheepToken Over a year ago

Sorry for that, I did not really test the code. You might want to check the type(node) instead of try/except but the idea is here :)

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