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Add an example of a custom validator

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Hynek Schlawack 2015-01-29 12:26:25 +01:00
parent 692e4613a0
commit 0e2507d51d
1 changed files with 18 additions and 2 deletions
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docs/examples.rst
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@ -104,7 +104,24 @@ More information on why class methods for constructing objects are awesome can b
Although your initializers should be a dumb as possible, it can come handy to do some kind of validation on the arguments.
That's when :func:`attr.ib`\ ’s ``validator`` argument comes into play.
A validator is simply a callable that takes two arguments: the attribute that it's validating
A validator is simply a callable that takes two arguments: the attribute that it's validating and the value that is passed for it.
If the value does not pass the validator's standards, it just raises an appropriate exception:
.. doctest::
>>> def smaller_than_5(attribute, value):
... if value >= 5:
... raise ValueError("'{name}' has to be smaller than 5!"
... .format(name=attribute.name))
>>> @attr.s
... class C(object):
... x = attr.ib(validator=smaller_than_5)
>>> C(42)
Traceback (most recent call last):
...
ValueError: 'x' has to be smaller than 5!
``attrs`` ships with a bunch of validators, make sure to :ref:`check them out <api_validators>` before writing your own:
.. doctest::
@ -118,4 +135,3 @@ A validator is simply a callable that takes two arguments: the attribute that it
...
TypeError: ("'x' must be <type 'int'> (got '42' that is a <type 'str'>).", Attribute(name='x', default_value=NOTHING, default_factory=NOTHING, validator=<instance_of validator for type <type 'int'>>), <type 'int'>, '42')
``attrs`` ships with a bunch of validators, make sure to :ref:`check them out <api_validators>` before writing your own!