Regex to catch code that uses private members in python, unless its a function def

You could try :

(?<!def\s)(\b__[a-zA-Z])

Example

source

Using ast.NodeVisitor it is very easy to get the attributes and a lot more reliable than a regex:

import inspect
import importlib
import ast

class FindAttr(ast.NodeVisitor):
    def visit_Attribute(self, node):
        print(node.attr)


mod = "test"
mod = importlib.import_module(mod)
p = ast.parse(inspect.getsource(mod))

f = FindAttr()
f.visit(p)

test.py:

class Foo(object):
    def __init__(self):
        self.__foo = "foo"

    def meth1(self):
        self.bar = "bar"

    def meth2(self):
        self.__foobar = "foobar"


    def meth3(self):
        self.blah = "foobar"
        return self.blah

Output:

In [7]: mod = "test"

In [8]: mod = importlib.import_module(mod)

In [9]: p = ast.parse(inspect.getsource(mod))

In [10]: f = FindAttr()

In [11]: f.visit(p)
__foo
bar
__foobar
blah

All you need to so is check if node.attr.startswith("__") etc.. You can visit any nodes you like, FunctionDef, ClassDef like shown here, there is a comprehensive list of all the nodes in the greentreesnakes docs and their attributes.