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author | Matt A. Tobin <mattatobin@localhost.localdomain> | 2018-02-02 04:16:08 -0500 |
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committer | Matt A. Tobin <mattatobin@localhost.localdomain> | 2018-02-02 04:16:08 -0500 |
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diff --git a/python/voluptuous/README.rst b/python/voluptuous/README.rst new file mode 100644 index 000000000..aa68a7cb4 --- /dev/null +++ b/python/voluptuous/README.rst @@ -0,0 +1,589 @@ +Voluptuous is a Python data validation library +============================================== + +|Build Status| |Stories in Ready| + +Voluptuous, *despite* the name, is a Python data validation library. It +is primarily intended for validating data coming into Python as JSON, +YAML, etc. + +It has three goals: + +1. Simplicity. +2. Support for complex data structures. +3. Provide useful error messages. + +Contact +------- + +Voluptuous now has a mailing list! Send a mail to +` <mailto:voluptuous@librelist.com>`__ to subscribe. Instructions will +follow. + +You can also contact me directly via `email <mailto:alec@swapoff.org>`__ +or `Twitter <https://twitter.com/alecthomas>`__. + +To file a bug, create a `new +issue <https://github.com/alecthomas/voluptuous/issues/new>`__ on GitHub +with a short example of how to replicate the issue. + +Show me an example +------------------ + +Twitter's `user search +API <https://dev.twitter.com/docs/api/1/get/users/search>`__ accepts +query URLs like: + +:: + + $ curl 'http://api.twitter.com/1/users/search.json?q=python&per_page=20&page=1 + +To validate this we might use a schema like: + +.. code:: pycon + + >>> from voluptuous import Schema + >>> schema = Schema({ + ... 'q': str, + ... 'per_page': int, + ... 'page': int, + ... }) + +This schema very succinctly and roughly describes the data required by +the API, and will work fine. But it has a few problems. Firstly, it +doesn't fully express the constraints of the API. According to the API, +``per_page`` should be restricted to at most 20, defaulting to 5, for +example. To describe the semantics of the API more accurately, our +schema will need to be more thoroughly defined: + +.. code:: pycon + + >>> from voluptuous import Required, All, Length, Range + >>> schema = Schema({ + ... Required('q'): All(str, Length(min=1)), + ... Required('per_page', default=5): All(int, Range(min=1, max=20)), + ... 'page': All(int, Range(min=0)), + ... }) + +This schema fully enforces the interface defined in Twitter's +documentation, and goes a little further for completeness. + +"q" is required: + +.. code:: pycon + + >>> from voluptuous import MultipleInvalid, Invalid + >>> try: + ... schema({}) + ... raise AssertionError('MultipleInvalid not raised') + ... except MultipleInvalid as e: + ... exc = e + >>> str(exc) == "required key not provided @ data['q']" + True + +...must be a string: + +.. code:: pycon + + >>> try: + ... schema({'q': 123}) + ... raise AssertionError('MultipleInvalid not raised') + ... except MultipleInvalid as e: + ... exc = e + >>> str(exc) == "expected str for dictionary value @ data['q']" + True + +...and must be at least one character in length: + +.. code:: pycon + + >>> try: + ... schema({'q': ''}) + ... raise AssertionError('MultipleInvalid not raised') + ... except MultipleInvalid as e: + ... exc = e + >>> str(exc) == "length of value must be at least 1 for dictionary value @ data['q']" + True + >>> schema({'q': '#topic'}) == {'q': '#topic', 'per_page': 5} + True + +"per\_page" is a positive integer no greater than 20: + +.. code:: pycon + + >>> try: + ... schema({'q': '#topic', 'per_page': 900}) + ... raise AssertionError('MultipleInvalid not raised') + ... except MultipleInvalid as e: + ... exc = e + >>> str(exc) == "value must be at most 20 for dictionary value @ data['per_page']" + True + >>> try: + ... schema({'q': '#topic', 'per_page': -10}) + ... raise AssertionError('MultipleInvalid not raised') + ... except MultipleInvalid as e: + ... exc = e + >>> str(exc) == "value must be at least 1 for dictionary value @ data['per_page']" + True + +"page" is an integer >= 0: + +.. code:: pycon + + >>> try: + ... schema({'q': '#topic', 'per_page': 'one'}) + ... raise AssertionError('MultipleInvalid not raised') + ... except MultipleInvalid as e: + ... exc = e + >>> str(exc) + "expected int for dictionary value @ data['per_page']" + >>> schema({'q': '#topic', 'page': 1}) == {'q': '#topic', 'page': 1, 'per_page': 5} + True + +Defining schemas +---------------- + +Schemas are nested data structures consisting of dictionaries, lists, +scalars and *validators*. Each node in the input schema is pattern +matched against corresponding nodes in the input data. + +Literals +~~~~~~~~ + +Literals in the schema are matched using normal equality checks: + +.. code:: pycon + + >>> schema = Schema(1) + >>> schema(1) + 1 + >>> schema = Schema('a string') + >>> schema('a string') + 'a string' + +Types +~~~~~ + +Types in the schema are matched by checking if the corresponding value +is an instance of the type: + +.. code:: pycon + + >>> schema = Schema(int) + >>> schema(1) + 1 + >>> try: + ... schema('one') + ... raise AssertionError('MultipleInvalid not raised') + ... except MultipleInvalid as e: + ... exc = e + >>> str(exc) == "expected int" + True + +URL's +~~~~~ + +URL's in the schema are matched by using ``urlparse`` library. + +.. code:: pycon + + >>> from voluptuous import Url + >>> schema = Schema(Url()) + >>> schema('http://w3.org') + 'http://w3.org' + >>> try: + ... schema('one') + ... raise AssertionError('MultipleInvalid not raised') + ... except MultipleInvalid as e: + ... exc = e + >>> str(exc) == "expected a URL" + True + +Lists +~~~~~ + +Lists in the schema are treated as a set of valid values. Each element +in the schema list is compared to each value in the input data: + +.. code:: pycon + + >>> schema = Schema([1, 'a', 'string']) + >>> schema([1]) + [1] + >>> schema([1, 1, 1]) + [1, 1, 1] + >>> schema(['a', 1, 'string', 1, 'string']) + ['a', 1, 'string', 1, 'string'] + +Validation functions +~~~~~~~~~~~~~~~~~~~~ + +Validators are simple callables that raise an ``Invalid`` exception when +they encounter invalid data. The criteria for determining validity is +entirely up to the implementation; it may check that a value is a valid +username with ``pwd.getpwnam()``, it may check that a value is of a +specific type, and so on. + +The simplest kind of validator is a Python function that raises +ValueError when its argument is invalid. Conveniently, many builtin +Python functions have this property. Here's an example of a date +validator: + +.. code:: pycon + + >>> from datetime import datetime + >>> def Date(fmt='%Y-%m-%d'): + ... return lambda v: datetime.strptime(v, fmt) + +.. code:: pycon + + >>> schema = Schema(Date()) + >>> schema('2013-03-03') + datetime.datetime(2013, 3, 3, 0, 0) + >>> try: + ... schema('2013-03') + ... raise AssertionError('MultipleInvalid not raised') + ... except MultipleInvalid as e: + ... exc = e + >>> str(exc) == "not a valid value" + True + +In addition to simply determining if a value is valid, validators may +mutate the value into a valid form. An example of this is the +``Coerce(type)`` function, which returns a function that coerces its +argument to the given type: + +.. code:: python + + def Coerce(type, msg=None): + """Coerce a value to a type. + + If the type constructor throws a ValueError, the value will be marked as + Invalid. + """ + def f(v): + try: + return type(v) + except ValueError: + raise Invalid(msg or ('expected %s' % type.__name__)) + return f + +This example also shows a common idiom where an optional human-readable +message can be provided. This can vastly improve the usefulness of the +resulting error messages. + +Dictionaries +~~~~~~~~~~~~ + +Each key-value pair in a schema dictionary is validated against each +key-value pair in the corresponding data dictionary: + +.. code:: pycon + + >>> schema = Schema({1: 'one', 2: 'two'}) + >>> schema({1: 'one'}) + {1: 'one'} + +Extra dictionary keys +^^^^^^^^^^^^^^^^^^^^^ + +By default any additional keys in the data, not in the schema will +trigger exceptions: + +.. code:: pycon + + >>> schema = Schema({2: 3}) + >>> try: + ... schema({1: 2, 2: 3}) + ... raise AssertionError('MultipleInvalid not raised') + ... except MultipleInvalid as e: + ... exc = e + >>> str(exc) == "extra keys not allowed @ data[1]" + True + +This behaviour can be altered on a per-schema basis. To allow additional +keys use ``Schema(..., extra=ALLOW_EXTRA)``: + +.. code:: pycon + + >>> from voluptuous import ALLOW_EXTRA + >>> schema = Schema({2: 3}, extra=ALLOW_EXTRA) + >>> schema({1: 2, 2: 3}) + {1: 2, 2: 3} + +To remove additional keys use ``Schema(..., extra=REMOVE_EXTRA)``: + +.. code:: pycon + + >>> from voluptuous import REMOVE_EXTRA + >>> schema = Schema({2: 3}, extra=REMOVE_EXTRA) + >>> schema({1: 2, 2: 3}) + {2: 3} + +It can also be overridden per-dictionary by using the catch-all marker +token ``extra`` as a key: + +.. code:: pycon + + >>> from voluptuous import Extra + >>> schema = Schema({1: {Extra: object}}) + >>> schema({1: {'foo': 'bar'}}) + {1: {'foo': 'bar'}} + +Required dictionary keys +^^^^^^^^^^^^^^^^^^^^^^^^ + +By default, keys in the schema are not required to be in the data: + +.. code:: pycon + + >>> schema = Schema({1: 2, 3: 4}) + >>> schema({3: 4}) + {3: 4} + +Similarly to how extra\_ keys work, this behaviour can be overridden +per-schema: + +.. code:: pycon + + >>> schema = Schema({1: 2, 3: 4}, required=True) + >>> try: + ... schema({3: 4}) + ... raise AssertionError('MultipleInvalid not raised') + ... except MultipleInvalid as e: + ... exc = e + >>> str(exc) == "required key not provided @ data[1]" + True + +And per-key, with the marker token ``Required(key)``: + +.. code:: pycon + + >>> schema = Schema({Required(1): 2, 3: 4}) + >>> try: + ... schema({3: 4}) + ... raise AssertionError('MultipleInvalid not raised') + ... except MultipleInvalid as e: + ... exc = e + >>> str(exc) == "required key not provided @ data[1]" + True + >>> schema({1: 2}) + {1: 2} + +Optional dictionary keys +^^^^^^^^^^^^^^^^^^^^^^^^ + +If a schema has ``required=True``, keys may be individually marked as +optional using the marker token ``Optional(key)``: + +.. code:: pycon + + >>> from voluptuous import Optional + >>> schema = Schema({1: 2, Optional(3): 4}, required=True) + >>> try: + ... schema({}) + ... raise AssertionError('MultipleInvalid not raised') + ... except MultipleInvalid as e: + ... exc = e + >>> str(exc) == "required key not provided @ data[1]" + True + >>> schema({1: 2}) + {1: 2} + >>> try: + ... schema({1: 2, 4: 5}) + ... raise AssertionError('MultipleInvalid not raised') + ... except MultipleInvalid as e: + ... exc = e + >>> str(exc) == "extra keys not allowed @ data[4]" + True + +.. code:: pycon + + >>> schema({1: 2, 3: 4}) + {1: 2, 3: 4} + +Recursive schema +~~~~~~~~~~~~~~~~ + +There is no syntax to have a recursive schema. The best way to do it is +to have a wrapper like this: + +.. code:: pycon + + >>> from voluptuous import Schema, Any + >>> def s2(v): + ... return s1(v) + ... + >>> s1 = Schema({"key": Any(s2, "value")}) + >>> s1({"key": {"key": "value"}}) + {'key': {'key': 'value'}} + +Extending an existing Schema +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Often it comes handy to have a base ``Schema`` that is extended with +more requirements. In that case you can use ``Schema.extend`` to create +a new ``Schema``: + +.. code:: pycon + + >>> from voluptuous import Schema + >>> person = Schema({'name': str}) + >>> person_with_age = person.extend({'age': int}) + >>> sorted(list(person_with_age.schema.keys())) + ['age', 'name'] + +The original ``Schema`` remains unchanged. + +Objects +~~~~~~~ + +Each key-value pair in a schema dictionary is validated against each +attribute-value pair in the corresponding object: + +.. code:: pycon + + >>> from voluptuous import Object + >>> class Structure(object): + ... def __init__(self, q=None): + ... self.q = q + ... def __repr__(self): + ... return '<Structure(q={0.q!r})>'.format(self) + ... + >>> schema = Schema(Object({'q': 'one'}, cls=Structure)) + >>> schema(Structure(q='one')) + <Structure(q='one')> + +Allow None values +~~~~~~~~~~~~~~~~~ + +To allow value to be None as well, use Any: + +.. code:: pycon + + >>> from voluptuous import Any + + >>> schema = Schema(Any(None, int)) + >>> schema(None) + >>> schema(5) + 5 + +Error reporting +--------------- + +Validators must throw an ``Invalid`` exception if invalid data is passed +to them. All other exceptions are treated as errors in the validator and +will not be caught. + +Each ``Invalid`` exception has an associated ``path`` attribute +representing the path in the data structure to our currently validating +value, as well as an ``error_message`` attribute that contains the +message of the original exception. This is especially useful when you +want to catch ``Invalid`` exceptions and give some feedback to the user, +for instance in the context of an HTTP API. + +.. code:: pycon + + >>> def validate_email(email): + ... """Validate email.""" + ... if not "@" in email: + ... raise Invalid("This email is invalid.") + ... return email + >>> schema = Schema({"email": validate_email}) + >>> exc = None + >>> try: + ... schema({"email": "whatever"}) + ... except MultipleInvalid as e: + ... exc = e + >>> str(exc) + "This email is invalid. for dictionary value @ data['email']" + >>> exc.path + ['email'] + >>> exc.msg + 'This email is invalid.' + >>> exc.error_message + 'This email is invalid.' + +The ``path`` attribute is used during error reporting, but also during +matching to determine whether an error should be reported to the user or +if the next match should be attempted. This is determined by comparing +the depth of the path where the check is, to the depth of the path where +the error occurred. If the error is more than one level deeper, it is +reported. + +The upshot of this is that *matching is depth-first and fail-fast*. + +To illustrate this, here is an example schema: + +.. code:: pycon + + >>> schema = Schema([[2, 3], 6]) + +Each value in the top-level list is matched depth-first in-order. Given +input data of ``[[6]]``, the inner list will match the first element of +the schema, but the literal ``6`` will not match any of the elements of +that list. This error will be reported back to the user immediately. No +backtracking is attempted: + +.. code:: pycon + + >>> try: + ... schema([[6]]) + ... raise AssertionError('MultipleInvalid not raised') + ... except MultipleInvalid as e: + ... exc = e + >>> str(exc) == "not a valid value @ data[0][0]" + True + +If we pass the data ``[6]``, the ``6`` is not a list type and so will +not recurse into the first element of the schema. Matching will continue +on to the second element in the schema, and succeed: + +.. code:: pycon + + >>> schema([6]) + [6] + +Running tests. +-------------- + +Voluptuous is using nosetests: + +:: + + $ nosetests + +Why use Voluptuous over another validation library? +--------------------------------------------------- + +**Validators are simple callables** + No need to subclass anything, just use a function. +**Errors are simple exceptions.** + A validator can just ``raise Invalid(msg)`` and expect the user to + get useful messages. +**Schemas are basic Python data structures.** + Should your data be a dictionary of integer keys to strings? + ``{int: str}`` does what you expect. List of integers, floats or + strings? ``[int, float, str]``. +**Designed from the ground up for validating more than just forms.** + Nested data structures are treated in the same way as any other + type. Need a list of dictionaries? ``[{}]`` +**Consistency.** + Types in the schema are checked as types. Values are compared as + values. Callables are called to validate. Simple. + +Other libraries and inspirations +-------------------------------- + +Voluptuous is heavily inspired by +`Validino <http://code.google.com/p/validino/>`__, and to a lesser +extent, `jsonvalidator <http://code.google.com/p/jsonvalidator/>`__ and +`json\_schema <http://blog.sendapatch.se/category/json_schema.html>`__. + +I greatly prefer the light-weight style promoted by these libraries to +the complexity of libraries like FormEncode. + +.. |Build Status| image:: https://travis-ci.org/alecthomas/voluptuous.png + :target: https://travis-ci.org/alecthomas/voluptuous +.. |Stories in Ready| image:: https://badge.waffle.io/alecthomas/voluptuous.png?label=ready&title=Ready + :target: https://waffle.io/alecthomas/voluptuous |