[PYTHON] duplicated function arguments when model properties have dollar symbols

Description

When model properties have dollar symbols $, then the swagger-codegen strips out these characters.
This can lead to duplicated function arguments (and also duplicated class members) in the Python code.

E.g. when a model has the properties bar and $bar:

definitions:
  Foo:
    properties:
      bar:
        type: integer
      $bar:
        type: string

This creates a class with an __init__ method with duplicated parameters:

class Foo(object):
    ...
    def __init__(self, bar=None, bar=None):  # noqa: E501
        self._bar = bar
        self._bar = bar

Swagger-codegen version

2.4.17
and
3.0.23

Swagger declaration file content or url

Full swagger file: https://gist.github.com/jakobkogler/d54d50e8188adf70a668b70d087f8a7e

Command line used for generation

./run-in-docker.sh generate -i foo.yaml -l python -o /gen/foo

Steps to reproduce

1. Download the swagger-file from the gist linked above.
2. Run ./run-in-docker.sh generate -i foo.yaml -l python -o /gen/foo
3. pip install -e foo
4. In a Python repl: import swagger_client fails because of duplicated function arguments

Related issues/PRs

https://github.com/swagger-api/swagger-codegen/issues/10276
https://github.com/swagger-api/swagger-codegen/issues/10447

Suggest a fix/enhancement

Looks like the dollar sign gets removed at https://github.com/swagger-api/swagger-codegen/blob/master/modules/swagger-codegen/src/main/java/io/swagger/codegen/languages/PythonClientCodegen.java#L397
Not sure what a good solution is, maybe replace $ with _dollar_, if the stripped out variable name clashes with another one.

Start at modules/swagger-codegen/src/main/java/io/swagger/codegen/languages/PythonClientCodegen.java around line 397 and reproduce with the linked gist, foo.yaml, and the run-in-docker.sh command. Check the generated Python model for collisions between bar and $bar; done means generation no longer creates duplicated arguments or class members and pip installation followed by import succeeds.