depot_tools/third_party/schema/README.rst

Schema validation just got Pythonic
===============================================================================

**schema** is a library for validating Python data structures, such as those
obtained from config-files, forms, external services or command-line
parsing, converted from JSON/YAML (or something else) to Python data-types.


.. image:: https://secure.travis-ci.org/keleshev/schema.png?branch=master
    :target: https://travis-ci.org/keleshev/schema

.. image:: https://img.shields.io/codecov/c/github/keleshev/schema.svg
    :target: http://codecov.io/github/keleshev/schema

Example
----------------------------------------------------------------------------

Here is a quick example to get a feeling of **schema**, validating a list of
entries with personal information:

.. code:: python

    >>> from schema import Schema, And, Use, Optional

    >>> schema = Schema([{'name': And(str, len),
    ...                   'age':  And(Use(int), lambda n: 18 <= n <= 99),
    ...                   Optional('sex'): And(str, Use(str.lower),
    ...                                        lambda s: s in ('male', 'female'))}])

    >>> data = [{'name': 'Sue', 'age': '28', 'sex': 'FEMALE'},
    ...         {'name': 'Sam', 'age': '42'},
    ...         {'name': 'Sacha', 'age': '20', 'sex': 'Male'}]

    >>> validated = schema.validate(data)

    >>> assert validated == [{'name': 'Sue', 'age': 28, 'sex': 'female'},
    ...                      {'name': 'Sam', 'age': 42},
    ...                      {'name': 'Sacha', 'age' : 20, 'sex': 'male'}]


If data is valid, ``Schema.validate`` will return the validated data
(optionally converted with `Use` calls, see below).

If data is invalid, ``Schema`` will raise ``SchemaError`` exception.


Installation
-------------------------------------------------------------------------------

Use `pip <http://pip-installer.org>`_ or easy_install::

    pip install schema

Alternatively, you can just drop ``schema.py`` file into your project—it is
self-contained.

- **schema** is tested with Python 2.6, 2.7, 3.2, 3.3 and PyPy.
- **schema** follows `semantic versioning <http://semver.org>`_.

How ``Schema`` validates data
-------------------------------------------------------------------------------

Types
~~~~~

If ``Schema(...)`` encounters a type (such as ``int``, ``str``, ``object``,
etc.), it will check if the corresponding piece of data is an instance of that type,
otherwise it will raise ``SchemaError``.

.. code:: python

    >>> from schema import Schema

    >>> Schema(int).validate(123)
    123

    >>> Schema(int).validate('123')
    Traceback (most recent call last):
    ...
    SchemaUnexpectedTypeError: '123' should be instance of 'int'

    >>> Schema(object).validate('hai')
    'hai'

Callables
~~~~~~~~~

If ``Schema(...)`` encounters a callable (function, class, or object with
``__call__`` method) it will call it, and if its return value evaluates to
``True`` it will continue validating, else—it will raise ``SchemaError``.

.. code:: python

    >>> import os

    >>> Schema(os.path.exists).validate('./')
    './'

    >>> Schema(os.path.exists).validate('./non-existent/')
    Traceback (most recent call last):
    ...
    SchemaError: exists('./non-existent/') should evaluate to True

    >>> Schema(lambda n: n > 0).validate(123)
    123

    >>> Schema(lambda n: n > 0).validate(-12)
    Traceback (most recent call last):
    ...
    SchemaError: <lambda>(-12) should evaluate to True

"Validatables"
~~~~~~~~~~~~~~

If ``Schema(...)`` encounters an object with method ``validate`` it will run
this method on corresponding data as ``data = obj.validate(data)``. This method
may raise ``SchemaError`` exception, which will tell ``Schema`` that that piece
of data is invalid, otherwise—it will continue validating.

An example of "validatable" is ``Regex``, that tries to match a string or a
buffer with the given regular expression (itself as a string, buffer or
compiled regex ``SRE_Pattern``):

.. code:: python

    >>> from schema import Regex
    >>> import re

    >>> Regex(r'^foo').validate('foobar')
    'foobar'

    >>> Regex(r'^[A-Z]+$', flags=re.I).validate('those-dashes-dont-match')
    Traceback (most recent call last):
    ...
    SchemaError: Regex('^[A-Z]+$', flags=re.IGNORECASE) does not match 'those-dashes-dont-match'

For a more general case, you can use ``Use`` for creating such objects.
``Use`` helps to use a function or type to convert a value while validating it:

.. code:: python

    >>> from schema import Use

    >>> Schema(Use(int)).validate('123')
    123

    >>> Schema(Use(lambda f: open(f, 'a'))).validate('LICENSE-MIT')
    <open file 'LICENSE-MIT', mode 'a' at 0x...>

Dropping the details, ``Use`` is basically:

.. code:: python

    class Use(object):

        def __init__(self, callable_):
            self._callable = callable_

        def validate(self, data):
            try:
                return self._callable(data)
            except Exception as e:
                raise SchemaError('%r raised %r' % (self._callable.__name__, e))

Now you can write your own validation-aware classes and data types.

Lists, similar containers
~~~~~~~~~~~~~~~~~~~~~~~~~

If ``Schema(...)`` encounters an instance of ``list``, ``tuple``, ``set`` or
``frozenset``, it will validate contents of corresponding data container
against schemas listed inside that container:


.. code:: python

    >>> Schema([1, 0]).validate([1, 1, 0, 1])
    [1, 1, 0, 1]

    >>> Schema((int, float)).validate((5, 7, 8, 'not int or float here'))
    Traceback (most recent call last):
    ...
    SchemaError: Or(<type 'int'>, <type 'float'>) did not validate 'not int or float here'
    'not int or float here' should be instance of 'float'

Dictionaries
~~~~~~~~~~~~

If ``Schema(...)`` encounters an instance of ``dict``, it will validate data
key-value pairs:

.. code:: python

    >>> d = Schema({'name': str,
    ...             'age': lambda n: 18 <= n <= 99}).validate({'name': 'Sue', 'age': 28})

    >>> assert d == {'name': 'Sue', 'age': 28}

You can specify keys as schemas too:

.. code:: python

    >>> schema = Schema({str: int,  # string keys should have integer values
    ...                  int: None})  # int keys should be always None

    >>> data = schema.validate({'key1': 1, 'key2': 2,
    ...                         10: None, 20: None})

    >>> schema.validate({'key1': 1,
    ...                   10: 'not None here'})
    Traceback (most recent call last):
    ...
    SchemaError: Key '10' error:
    None does not match 'not None here'

This is useful if you want to check certain key-values, but don't care
about other:

.. code:: python

    >>> schema = Schema({'<id>': int,
    ...                  '<file>': Use(open),
    ...                  str: object})  # don't care about other str keys

    >>> data = schema.validate({'<id>': 10,
    ...                         '<file>': 'README.rst',
    ...                         '--verbose': True})

You can mark a key as optional as follows:

.. code:: python

    >>> from schema import Optional
    >>> Schema({'name': str,
    ...         Optional('occupation'): str}).validate({'name': 'Sam'})
    {'name': 'Sam'}

``Optional`` keys can also carry a ``default``, to be used when no key in the
data matches:

.. code:: python

    >>> from schema import Optional
    >>> Schema({Optional('color', default='blue'): str,
    ...         str: str}).validate({'texture': 'furry'}
    ...       ) == {'color': 'blue', 'texture': 'furry'}
    True

Defaults are used verbatim, not passed through any validators specified in the
value.

**schema** has classes ``And`` and ``Or`` that help validating several schemas
for the same data:

.. code:: python

    >>> from schema import And, Or

    >>> Schema({'age': And(int, lambda n: 0 < n < 99)}).validate({'age': 7})
    {'age': 7}

    >>> Schema({'password': And(str, lambda s: len(s) > 6)}).validate({'password': 'hai'})
    Traceback (most recent call last):
    ...
    SchemaError: Key 'password' error:
    <lambda>('hai') should evaluate to True

    >>> Schema(And(Or(int, float), lambda x: x > 0)).validate(3.1415)
    3.1415

Extra Keys
~~~~~~~~~~

The ``Schema(...)`` parameter ``ignore_extra_keys`` causes validation to ignore extra keys in a dictionary, and also to not return them after validating.

.. code:: python

    >>> schema = Schema({'name': str}, ignore_extra_keys=True)
    >>> schema.validate({'name': 'Sam', 'age': '42'})
    {'name': 'Sam'}

If you would like any extra keys returned, use ``object: object`` as one of the key/value pairs, which will match any key and any value.
Otherwise, extra keys will raise a ``SchemaError``.

User-friendly error reporting
-------------------------------------------------------------------------------

You can pass a keyword argument ``error`` to any of validatable classes
(such as ``Schema``, ``And``, ``Or``, ``Regex``, ``Use``) to report this error
instead of a built-in one.

.. code:: python

    >>> Schema(Use(int, error='Invalid year')).validate('XVII')
    Traceback (most recent call last):
    ...
    SchemaError: Invalid year

You can see all errors that occurred by accessing exception's ``exc.autos``
for auto-generated error messages, and ``exc.errors`` for errors
which had ``error`` text passed to them.

You can exit with ``sys.exit(exc.code)`` if you want to show the messages
to the user without traceback. ``error`` messages are given precedence in that
case.

A JSON API example
-------------------------------------------------------------------------------

Here is a quick example: validation of
`create a gist <http://developer.github.com/v3/gists/>`_
request from github API.

.. code:: python

    >>> gist = '''{"description": "the description for this gist",
    ...            "public": true,
    ...            "files": {
    ...                "file1.txt": {"content": "String file contents"},
    ...                "other.txt": {"content": "Another file contents"}}}'''

    >>> from schema import Schema, And, Use, Optional

    >>> import json

    >>> gist_schema = Schema(And(Use(json.loads),  # first convert from JSON
    ...                          # use basestring since json returns unicode
    ...                          {Optional('description'): basestring,
    ...                           'public': bool,
    ...                           'files': {basestring: {'content': basestring}}}))

    >>> gist = gist_schema.validate(gist)

    # gist:
    {u'description': u'the description for this gist',
     u'files': {u'file1.txt': {u'content': u'String file contents'},
                u'other.txt': {u'content': u'Another file contents'}},
     u'public': True}

Using **schema** with `docopt <http://github.com/docopt/docopt>`_
-------------------------------------------------------------------------------

Assume you are using **docopt** with the following usage-pattern:

    Usage: my_program.py [--count=N] <path> <files>...

and you would like to validate that ``<files>`` are readable, and that
``<path>`` exists, and that ``--count`` is either integer from 0 to 5, or
``None``.

Assuming **docopt** returns the following dict:

.. code:: python

    >>> args = {'<files>': ['LICENSE-MIT', 'setup.py'],
    ...         '<path>': '../',
    ...         '--count': '3'}

this is how you validate it using ``schema``:

.. code:: python

    >>> from schema import Schema, And, Or, Use
    >>> import os

    >>> s = Schema({'<files>': [Use(open)],
    ...             '<path>': os.path.exists,
    ...             '--count': Or(None, And(Use(int), lambda n: 0 < n < 5))})

    >>> args = s.validate(args)

    >>> args['<files>']
    [<open file 'LICENSE-MIT', mode 'r' at 0x...>, <open file 'setup.py', mode 'r' at 0x...>]

    >>> args['<path>']
    '../'

    >>> args['--count']
    3

As you can see, **schema** validated data successfully, opened files and
converted ``'3'`` to ``int``.