How to parse individual variables from python code in case of multiple variables assignments?

Question

I have this simple python code example that parses a python code and extracts the variables assigned in it:

import ast
import sys
import astunparse
import json

tree=ast.parse('''\
a = 10
b,c=5,6
[d,e]=7,8
(f,g)=9,10
h=20
''',mode="exec")

for thing in tree.body:
    if isinstance(thing, ast.Assign):
        print(astunparse.unparse(thing).split('=')[0].strip())

I also tried a similar method with a NodeVisitor:

import ast
import sys
import astunparse
import json

tree=ast.parse('''\
a = 10
b,c=5,6
[d,e]=7,8
(f,g)=9,10
h=20
''',mode="exec")

class AnalysisNodeVisitor2(ast.NodeVisitor):
    def visit_Assign(self,node):
        print(astunparse.unparse(node.targets))
        
Analyzer=AnalysisNodeVisitor2()
Analyzer.visit(tree)

But both methods gave me this same results:

a
(b, c)
[d, e]
(f, g)
h

But the output I'm trying to get is individual variables like this:

a
b
c
d
e
f
g
h

Is there a way to achieve this?

chepner · Accepted Answer · 2021-02-09 20:26:18Z

2

Each target is either an object with an id attribute, or a sequence of targets.

for thing in tree.body:
    if isinstance(thing, ast.Assign):
        for t in thing.targets:
            try:
                print(t.id)
            except AttributeError:
                for x in t.elts:
                    print(x.id)

This, of course, doesn't handle more complicated possible assignments like a, (b, c) = [3, [4,5]], but I leave it as an exercise to write a recursive function that walks the tree, printing target names as they are found. (You may also need to adjust the code to handle things like a[3] = 5 or a.b = 10.)

edited Feb 9, 2021 at 20:26

answered Feb 9, 2021 at 20:03

chepner

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3 Comments

wazzup Over a year ago

Thank you for the explanation, but I just tried it and I get "AttributeError: 'Assign' object has no attribute 'elts'" at the first assignment which is the a=10 so thing in my case has neither an id attribute nor elts attribute?

chepner Over a year ago

Sorry, I had a working test, then tried to reproduce it here from memory and completely forgot about the targets attribute. I'll update.

wazzup Over a year ago

Thank you very helpful.

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