[BUG][Python] Some regex patterns can generate invalid code.

Created by: RedRoserade

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

If a pattern such as ^['"\-\w\s]+$ is specified, the generated python code for validation produces a syntax error:

        if self.api_client.client_side_validation and 'search_string' in local_var_params and not re.search(r'^[\'"\-\w\s]+$', local_var_params['search_string']):  # noqa: E501
            raise ApiValueError("Invalid value for parameter `search_string` when calling `example`, must conform to the pattern `/^['"\-\w\s]+$/`")  # noqa: E501
                                                                                                                            #       --^

However, if it is changed to ^[\'\"\-\w\s]+$, the error then becomes:

        if self.api_client.client_side_validation and 'search_string' in local_var_params and not re.search(r'^[\\'\"\-\w\s]+$', local_var_params['search_string']):  # noqa: E501
                                                                                                            #  ---^
            raise ApiValueError("Invalid value for parameter `search_string` when calling `example`, must conform to the pattern `/^[\'\"\-\w\s]+$/`")  # noqa: E501

The pattern ^['\"\-\w\s]+$ works, since the generated code has the correct escape sequences, but as far as I can tell, it is equivalent to the others (despite the redundant escapes).

openapi-generator version

I'm using version v4.3.1.

OpenAPI declaration file content or url

swagger: '2.0'
info:
  version: 1.0.0
  title: Example
consumes:
  - application/json
produces:
  - application/json
paths:
  /example:
    get:
      operationId: example
      parameters:
        - name: search_string
          in: query
          required: true
          type: string
          minLength: 1
          maxLength: 256
          pattern: ^['"\-\w\s]+$
      responses:
        '200':
          description: OK

##### Command line used for generation

docker run --rm
-v "$(pwd):/local"
--user="$(id -u):$(id -g)"
-w /local
openapitools/openapi-generator-cli:v4.3.1 generate
-i "swagger.yaml"
-g python
-o .
-c example.json

```json
{
  "packageName": "example",
  "projectName": "example",
  "packageVersion": "1.0.0"
}

Related issues/PRs

• https://github.com/OpenAPITools/openapi-generator/issues/5582

Suggest a fix

I would like to fix this, if possible.