Add migration documentation for 0.x -> 1.0

Fixes ua-parser#181

doc/advanced/migration.rst

@@ -0,0 +1,131 @@
+===============
+From 0.x to 1.0
+===============
+
+Don't Touch A Thing
+===================
+
+The first and simplest way to transition is to not transition: the 0.x
+API won't be removed for a long time, possibly ever. While it is
+unlikely to get updated any further and will eventually (hopefully?)
+fall behind, if you can't be arsed you probably don't have to until an
+unlikely 2.0.
+
+Unavoidable Divergences
+=======================
+
+Although the 1.0 API aims to be reasonably bridge-able to
+0.x-compatible code, a few items may be cause for concern and require
+special attention:
+
+- The 1.0 API supports :data:`ua_parser.UserAgent.patch_minor
+  <ua_parser.UserAgent>`, which may be a concern if the program stores
+  match results and compares them exactly.
+- The global parser of the 1.0 API is instantiated lazily on-demand,
+  this may cause unexpected runtime loads and can be remediated by
+  explicitly accessing the parser on load e.g.::
+
+      import ua_parser
+      # force initialisation of global parser
+      ua_parser.parser
+
+- The 1.0 API defaults to an :class:`re2-based parser
+  <ua_parser.re2.Resolver>` if |re2|_ is installed, although it seems
+  unlikely you may wish to consider replacing it with configuring a
+  :class:`~ua_parser.Parser` with a :class:`ua_parser.basic.Resolver`
+  if |re2|_ is one of your dependencies.
+
+Default Ruleset
+===============
+
+While the 1.0 API was designed to better respect :pep:`8` and support
+:mod:`typing`, it was also designed to easily be transitioned from.
+
+Given a 0.x API not using YAML, the conversion should be very easy and
+consists of:
+
+- updating the import from ``ua_parser.user_agent_parser`` to just
+  ``ua_parser``
+- lowercasing the function names
+- adding :meth:`~ua_parser.Result.with_defaults()` after the function
+  call
+- wrapping the entire thing in :func:`dataclasses.asdict`
+
+For example, given
+
+..
+    >>> from pprint import pprint
+    >>> ua_string = 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2272.104 Safari/537.36'
+
+.. code-block:: pycon
+
+  >>> from ua_parser import user_agent_parser
+  >>> pprint(user_agent_parser.Parse(ua_string))  # doctest: +NORMALIZE_WHITESPACE
+  {'device': {'brand': 'Apple', 'family': 'Mac', 'model': 'Mac'},
+   'os': {'family': 'Mac OS X',
+          'major': '10',
+          'minor': '9',
+          'patch': '4',
+          'patch_minor': None},
+   'string': 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_4) AppleWebKit/537.36 '
+             '(KHTML, like Gecko) Chrome/41.0.2272.104 Safari/537.36',
+   'user_agent': {'family': 'Chrome',
+                  'major': '41',
+                  'minor': '0',
+                  'patch': '2272'}}
+
+the 1.0 version would be:
+
+.. code-block:: pycon
+
+  >>> import dataclasses
+  >>> import ua_parser
+  >>> pprint(dataclasses.asdict(ua_parser.parse(ua_string).with_defaults()))  # doctest: +NORMALIZE_WHITESPACE
+  {'device': {'brand': 'Apple', 'family': 'Mac', 'model': 'Mac'},
+   'os': {'family': 'Mac OS X',
+          'major': '10',
+          'minor': '9',
+          'patch': '4',
+          'patch_minor': None},
+   'string': 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_4) AppleWebKit/537.36 '
+             '(KHTML, like Gecko) Chrome/41.0.2272.104 Safari/537.36',
+   'user_agent': {'family': 'Chrome',
+                  'major': '41',
+                  'minor': '0',
+                  'patch': '2272',
+                  'patch_minor': '104'}}
+
+.. note::
+
+   - by default, the 1.0 API simply leaves entries ``None`` when no
+     data was matched, :meth:`~ua_parser.Result.with_defaults()`
+     fills them with the default value for the domain matching the 0.x API
+   - the 1.0 API returns :class:`typed dataclasses rather than untyped
+     dicts <ua_parser.core.UserAgent>`, hence the necessary conversion
+     to dict
+
+YAML Ruleset
+============
+
+The 1.0 API does not support :envvar:`UA_PARSER_YAML` anymore, instead
+it provides a layered API which lets clients use multiple parsers at
+the same time, and load rulesets from various datasources.
+
+Legacy YAML support can be added via a pretty small shim::
+
+  import ua_parser
+  from ua_parser.loaders import load_yaml
+
+  if yaml_path = os.environ.get("UA_PARSER_YAML"):
+      ua_parser.parser = ua_parser.Parser.from_matchers(
+          load_yaml(yaml_path))
+
+This will load the YAML file, create a parser from it, and set the new
+parser as the global parser used by the top-level utility functions.
+
+.. seealso::
+
+   - :ref:`guide-custom-rulesets`
+   - :ref:`guide-custom-global-parser`
+   - :ref:`api-loading`
+

doc/api.rst

@@ -59,7 +59,7 @@ Base Resolvers
 --------------
 
 Base resolvers take sets of :class:`~ua_parser.core.Matchers`
-generated by :ref:`loaders <Loading>`, and use them to extract data
+generated by :ref:`loaders <api-loading>`, and use them to extract data
 from user agent strings.
 
 .. autoclass:: ua_parser.basic.Resolver(Matchers)
@@ -129,7 +129,7 @@ basic resolver <ua_parser.basic.Resolver>`.
 
 .. autoclass:: Local
 
-.. _loading:
+.. _api-loading:
 
 Loading
 -------

doc/guides.rst

@@ -2,6 +2,8 @@
 Guides
 ======
 
+.. _guide-custom-rulesets:
+
 Custom Rulesets
 ===============
 
@@ -36,6 +38,8 @@ ua-parser provides easy ways to load custom rolesets:
    parser = Parser.from_matchers(load_yaml("regexes.yaml"))
    parser.parse(some_ua)
 
+.. _guide-custom-global-parser:
+
 Custom Global Parser
 ====================
 

doc/index.rst

@@ -17,3 +17,4 @@ For more detailed insight and advanced uses, see the :doc:`api` and
    guides
    api
    advanced/caches
+   advanced/migration