validoot 1.0

Simple validation for function arguments using a decorator.

This module is designed to solve the most basic of argument validations: types, clauses, and combinations of clauses. It is meant to remove some of the boiler plate code used to check the input types and checks such as between, or string lengths.

Github url: https://github.com/AstromechZA/validoot

Pypi url: https://pypi.python.org/pypi/validoot/1.0

Definitions

• Clause - A function that takes in the value as a parameter and returns True or False.

• Operator - Allows you to “and” and “or” clauses together.

Basic example:

from validoot import validates, inst, typ, between

@validates(inst(basestring), typ(int), between(0, 100))
def do_something(name, id, age):
    pass

In the code above, a validoot.ValidationError will be thrown if the name is not a string or unicode, if the id is not an integer, or if the age is not between 0 and 100.

Operators:

We can extend the first example by adding an additional check for the name: it must be between 5 and 40 characters. For this we use the validoot.And operator to combine the clauses.

from validoot import validates, inst, typ, between, len_between, And

@validates(And(inst(basestring), len_between(5, 40)), typ(int), between(0, 100))
def do_something(name, id, age):
    pass

An Or operator also exists. Both And and Or take in a variable number of clauses and can be nested further.

Operator shortcuts are provided for joining clauses in a different manner which reads differently (._and(...), ._or(...)). So our previous example can be changed to look like this:

from validoot import validates, inst, typ, between, len_between

@validates(inst(basestring)._and(len_between(5, 40)), typ(int), between(0, 100))
def do_something(name, id, age):
    pass

Keyword arguments:

There is also support for keyword arguments:

from validoot import validates, inst, typ

@validates(inst(basestring), something=typ(float))
def do_something(name, something=1.0, anotherthing=2):
    pass

Here the something value must pass the validation checks as specified in the decorator. No checks exist for anotherthing so it has no restrictions.

Additional Clauses:

There are some more complex clauses included with the package:

• _ : The underscore only allows NoneType.

• numeric : Only accepts int, float, or long types.

• text : Only accepts instances of basestring (Python 2) or str (Python 3).

These can be found in the validoot.builtins module.

FAQ:

What if I don’t want validation for one of the position arguments?

Simple. Just use None.

from validoot import validates, inst, between

@validates(inst(basestring), None, between(0, 100))
def do_something(name, id, age):
    pass

What validation clauses are built in?

• typ(t) - value must be of exact type t

• inst(t) - value must be of exact type t or of subclass

• between(lower, upper, lower_inc=True, upper_inc=False) - the value must between lower and upper. lower_inc and upper_inc indicate range inclusivity.

• len_between(...) - identical to between but uses len(value)

• not_negative() - value cannot be negative

How do I create my own validation clauses?

The built in clauses provided by Validoot are all subclasses of the validoot.clauses.Clause object. Check out its source code to see how they work. Technically clauses can be any callable object so plain functions or lambdas also work.