[python-flask] regex pattern causes generation fails.

[HugoMario]

Description

Having a property with regex pattern, inside a model, makes generation process crash. This is because according commit a4d4b0 Python has a different regex convention for modifier.

Swagger-codegen version

2.4.1

Swagger declaration file content or url

swagger: "2.0"
info:
  description: "allOf issue demonstration"
  version: "1.0.0"
  title: "Swagger allOf regression"
host: "example.com"
schemes:
- "http"
paths:
  /rides:
    post:
      tags:
      - "rides"
      summary: "Add a new ride"
      description: ""
      operationId: "addRide"
      parameters:
      - in: "body"
        name: "body"
        description: "Ride object"
        required: true
        schema:
          $ref: "#/definitions/Ride"
      responses:
        405:
          description: "Invalid input"
definitions:
  Ride:
    type: "object"
    required:
    - "from"
    - "to"
    properties:
      id:
        type: "integer"
        format: "int64"
      from:
        type: "string"
        example: "London"
      to:
        type: "string"
        example: "Manchester"
      date-time:  
        $ref: '#/definitions/GLOBAL_DateTime'
  GLOBAL_DateTime:
    type: string
    format: date-time
    pattern: '[0-9]{4}-[0-9]{2}-[0-9]{2}T[0-9]{2}:[0-9]{2}:[0-9]{2}(.[0-9]{1,7})?Z'

Suggest a fix/enhancement

I'm not familiar with Python, playing a bit with this issue i placed a / at beginning and at end on pattern and seems to work, but that looks more like a hack instead a real solution.

So any suggestion is welcome