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Get and validate all Flask input parameters with ease.

Project description

Flask Parameter Validation

Get and validate all Flask input parameters with ease.


  • Pip: Install with pip install flask_parameter_validation.
  • Manually:
    • git clone
    • python install

Simple Usage

from flask import Flask
from typing import List, Optional
from flask_parameter_validation import ValidateParameters, Route, Json, Query
from datetime import datetime

app = Flask(__name__)

@app.route("/update/<int:id>", methods=["POST"])
def hello(
        id: int = Route(),
        username: str = Json(min_str_length=5, blacklist="<>"),
        age: int = Json(min_int=18, max_int=99),
        nicknames: List[str] = Json(),
        date_of_birth: datetime = Json(),
        password_expiry: Optional[int] = Json(5),
        is_admin: bool = Query(False)
    return "Hello World!"

if __name__ == "__main__":

Detailed Usage

  1. We use the ValidateParameters decorator on all functions that this modules should be used in.
  2. The format for arguments is as follows: parameter_name: parameter_type = Class() In this example, parameter_name would be the field name itself, such as "username". parameter_type would be the expected python data type, such as str, int, List, Union etc. Finally, Class() is one of the class inputs, as detailed below:


  1. Route()
    This is the data passed through the URL, such as /users/<int:id>
  2. Form()
    This is the data passed by a normal HTML form, often with x-www-form-urlencoded content-type.
  3. Json()
    This is any JSON body sent -- request must have application/json content type for flask to read this.
  4. Query()
    This covers query parameters (aka GET parameters), such as /news/article?id=55
  5. File()
    The validation on files are different to the others, but file input can still be obtained here as their Flask FileStorage objects.

Input types

  • str
  • int
  • bool
  • float
  • typing.List
  • typing.Union
  • typing.Optional
  • datetime.datetime


All parameters can have default values, and automatic validation.
Route, Form, Json and Query have the following options:

  • default: any, Specifies the default value for the field.
  • min_str_length: int, Specifies the minimum character length for a string input
  • max_str_length: int, Specifies the maximum character length for a string input
  • min_list_length: int, Specifies the minimum number of elements in a list
  • max_list_length: int, Specifies the maximum number of elements in a list
  • min_int: int, Specifies the minimum number for an int input
  • max_int: int, Specifies the maximum number for an int input
  • whitelist: str, A string containing allowed characters for the value
  • blacklist: str, A string containing forbidden characters for the value
  • pattern: str, A regex pattern to test for string matches
  • func: Callable, A function containing a fully customized logic to validate the value

File has the following options:

  • content_types: array of strings, an array of allowed content types.
  • min_length: Minimum content-length for a file
  • max_length: Maximum content-length for a file

These validators are passed into the classes in the route function, such as:

  • username: str = Json("defaultusername", min_length=5)
  • profile_picture: Any = File(content_types=["image/png", "image/jpeg"])
  • filter: str = Query()

Overwriting default errors

By default, the error messages are returned as a JSON response, with the detailed error in the "error" field. However, this can be edited by passing a custom error function into the ValidateParameters decorator. For example:

def error_handler(err):
    error_name = type(err)
    error_parameters = err.args
    error_message = str(err)
    return {
        "error_name": type(err).__name__,
        "error_parameters": err.args,
        "error_message": str(err)
    }, 400

def api(...)

Project details

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