Parsing literal assignments from a Python file

Question

Sought: A Python 3 library (hopefully also supporting Python 2) that takes a Python file containing assignments of literal values (specifically, anything parseable by ast.literal_eval) to variables and returns a dict of the resulting namespace. If the file contains any non-literal assignments, the library either raises an error or ignores them.

For example, the library should be able to turn a file like this:

foo = 42
bar = [{"quux": None, "glarch": True}]
foo = 'reassigned'

into the value:

{
    "bar": [{"quux": None, "glarch": True}],
    "foo": "reassigned"
}

and a file like this:

foo = range(42)
bar = 2 + 2
quux = input()
glarch = 'Hi!'

would either produce an error or end up as just {"glarch": "Hi!"} without actually running the range() or input() (Bonus points if it can parse the bar = 2 + 2, though).

(I could've sworn I'd seen a library like this before, possibly as part of Django, but I can't find it anymore.)

Answer 1

I don't know of a library for this specific task, but it's easy to do it with ast.parse. Here's an example in Python 3:

import ast

with open("myfile.py", "r") as o:
    src = o.read()
top_level = ast.parse(src)

result = {}
for statement in top_level.body:
    assert isinstance(statement, ast.Assign)
    assert len(statement.targets) == 1
    name = statement.targets[0].id
    result[name] = ast.literal_eval(statement.value)

print(result)

If the input is:

 foo = 42
 bar = [{"quux": None, "glarch": True}]
 foo = 'reassigned'
 bing = 1 + 1

Then you get:

{'bing': 2, 'foo': 'reassigned', 'bar': [{'glarch': True, 'quux': None}]}