Validation

This page describes the coola.validation package, which provides a small set of functions to validate function/method arguments and raise a standard exception with a clear error message when a constraint is not met.

Prerequisites: You'll need to know a bit of Python. For a refresher, see the Python tutorial.

Overview

The coola.validation package provides:

1. Type checks - validate_isinstance to check a value is an instance of a given type
2. Container checks - validate_not_empty to check a value is not empty, and validate_in to check a value belongs to a set of valid values
3. Comparison checks - validate_ge, validate_gt, validate_le, and validate_lt to check a value against a bound

Every function takes the value to validate as its first argument, and an optional name keyword argument used to identify the value in the error message. On success, the function returns None; on failure, it raises an exception.

Type

>>> from coola.validation import validate_isinstance
>>> validate_isinstance(1, int)
>>> validate_isinstance(1, (int, float))
>>> validate_isinstance("abc", int, name="count")
Traceback (most recent call last):
    ...
TypeError: count must be an instance of <class 'int'>, got <class 'str'>

Container

>>> from coola.validation import validate_not_empty
>>> validate_not_empty([1, 2, 3])
>>> validate_not_empty([], name="my_list")
Traceback (most recent call last):
    ...
ValueError: my_list must not be empty

>>> from coola.validation import validate_in
>>> validate_in("a", ("a", "b", "c"))
>>> validate_in("d", ("a", "b", "c"), name="mode")
Traceback (most recent call last):
    ...
ValueError: mode must be one of ('a', 'b', 'c'), got 'd'

Comparison

validate_ge/validate_le check inclusive bounds, and validate_gt/validate_lt check exclusive bounds:

>>> from coola.validation import validate_ge, validate_gt, validate_le, validate_lt
>>> validate_ge(1, 0)
>>> validate_gt(1, 0)
>>> validate_le(0, 1)
>>> validate_lt(0, 1)
>>> validate_gt(1, 1, name="count")
Traceback (most recent call last):
    ...
ValueError: count must be greater than 1, got 1

See Also

• coola.identifier: Uses a similar internal validation helper module for its generators.