[BUG] [python-flask] A backslash-character pair generates a SyntaxWarning from Python 3.12

[jops-wtakase]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

When I run the python-flask generator, some generated models output SyntaxWarning in Python 3.12. This issue is caused by the {{{pattern}}} in the line here, which may contain a backslash (\), making the string a potential source of warnings.

Introduced feature in Python 3.12

Starting from Python 3.12, a backslash-character pair generates a SyntaxWarning instead of a DeprecationWarning. In future Python versions, this will be escalated to a SyntaxError.

openapi-generator version

Latest master branch (1518237)

OpenAPI declaration file content or url

example.yaml

openapi: "3.0.3"
info:
  title: Example
  version: 1.0.0
servers: 
  - url: "http://localhost:3000"
paths: 
 "/example":
    get: 
      responses:
        '200':
          description: example response
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Example'
components:
  schemas:
    Example:
      title: Example
      description: Example
      type: object
      properties:
        name:
          type: string
          pattern: '^[a-zA-Z0-9]+[a-zA-Z0-9\.\-_]*[a-zA-Z0-9]+$'

Generation Details

java -jar openapi-generator-cli.jar \
    generate \
    -i /tmp/example.yaml \
    -g python-flask \
    --additional-properties packageName=example \
    -o /tmp/example

Steps to reproduce

docker run -v /tmp/example/example/models/example.py:/example.py -w /models --rm python:3.12-alpine python -Wa -m py_compile /example.py

/example.py:63: SyntaxWarning: invalid escape sequence '\.'
  raise ValueError("Invalid value for `name`, must be a follow pattern or equal to `/^[a-zA-Z0-9]+[a-zA-Z0-9\.\-_]*[a-zA-Z0-9]+$/`")  # noqa: E501

Related issues/PRs

None found. Searched using the keyword SyntaxWarning, but no relevant issues/PRs were identified.

Suggest a fix

Modify the line in modules/openapi-generator/src/main/resources/python-flask/model.mustache from:

            raise ValueError("Invalid value for `{{name}}`, must be a follow pattern or equal to `{{{pattern}}}`")  # noqa: E501

to:

            raise ValueError(r"Invalid value for `{{name}}`, must be a follow pattern or equal to `{{{pattern}}}`")  # noqa: E501