How to validate parameters in Flask - api

Question

Is there a way to validate a sting in Flask to check for the following. I am looking for it to not only show up in the Swagger documentation but to also catch it as a string validation error if possible
Min length 10
Max length 1,024
Starts with [a-zA-Z]
Contains [a-zA-Z0-9=!##$%^&*()-]
Ends with [a-zA-z0-9]
Here is how I have my endpoint set up so far
from flask import Flask
from flask_restplus import Api, Resource, fields
flask_app= Flask (__name__)
app = Api(app = flask_app,
version = "1.0",
title = "Test API",
description = "Example endpoint to test validation of POST body parameter using Flaskplus")
model = app.model (
'username model',
{
'username': fields.String (
required = True,
description = "Username of the user",
help = "Username cannot be blank, must be of length 10, can start with an upper or lower case letter, can contain upper/lower case, numbers, and the following special characters [=!##$%^&*()-], and must end with an upper/lower case letter or a number",
example = "john.smith123"
)
}
)
name_space = app.namespace ('', 'Main API')
#name_space.route ("/test")
class test (Resource)
#app.doc(
responses = {
200: 'OK',
400: 'Invalid Argument',
500: 'Mapping Key Error'
}
)
#app.expect (model)
def post (self):
try:
username = request.json.get('username')
return {
'status': 'Username valid',
'status_code': 200
}
except KeyError as e:
name_space.abort (
500,
e.__doc__,
status = "Key error",
statusCode = "500"
)

Answer 1

You can use the flask-parameter-validation project in order to do this. You'll be able to implement it with something similar to the following:
from flask_parameter_validation import ValidateParameters, Json
#name_space.route("/test", methods=["POST"])
#ValidateParameters()
def hello(
username: str = Json(
min_str_length=10,
max_str_length=1024,
pattern=r"REGEX"
)
):
return f"Hello, {username}"
You'll need to replace REGEX with a regex pattern that fulfills your start, middle and end criteria.
Hope that this helps!