[Python] refactor pydantic model methods into abstract python codegen (#16279)

* refactor methods from python client to abstract python codegen

* refactor regular expression methods

* more refactoring

* more refactoring

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/PythonFastAPIServerCodegen.java

@@ -321,12 +321,6 @@ public class PythonFastAPIServerCodegen extends AbstractPythonCodegen {
         System.out.println("################################################################################");
     }
 
-    @Override
-    public String toRegularExpression(String pattern) {
-        String regex = super.toRegularExpression(pattern);
-        return StringUtils.substring(regex, 1, -1);
-    }
-
     @Override
     public String generatorLanguageVersion() { return "3.7"; };
 }

samples/server/petstore/python-fastapi/src/openapi_server/apis/user_api.py

@@ -138,7 +138,7 @@ async def get_user_by_name(
     response_model_by_alias=True,
 )
 async def login_user(
-    username: str = Query(None, description="The user name for login", regex=r"^[a-zA-Z0-9]+[a-zA-Z0-9\.\-_]*[a-zA-Z0-9]+$"),
+    username: str = Query(None, description="The user name for login", regex=r"/^[a-zA-Z0-9]+[a-zA-Z0-9\.\-_]*[a-zA-Z0-9]+$/"),
     password: str = Query(None, description="The password for login in clear text"),
 ) -> str:
     """"""

samples/server/petstore/python-fastapi/src/openapi_server/models/category.py

@@ -25,7 +25,7 @@ class Category(BaseModel):
 
     @validator("name")
     def name_pattern(cls, value):
-        assert value is not None and re.match(r"^[a-zA-Z0-9]+[a-zA-Z0-9\.\-_]*[a-zA-Z0-9]+$", value)
+        assert value is not None and re.match(r"/^[a-zA-Z0-9]+[a-zA-Z0-9\.\-_]*[a-zA-Z0-9]+$/", value)
         return value
 
 Category.update_forward_refs()