10
bzrlib has a rich API which is used both internally, and externally by
11
plugins and scripts. To allow the API to change, specifically to allow
12
support for features and methods to be removed, without causing hard to
13
diagnose bugs in the clients of the API, bzrlib provides explicit API
14
compatibility data, and a compact API to allow scripts and plugins to
15
ascertain if the bzrlib they are using is compatible to the API they were
25
To allow plugins to apply their own policy for compatibility with bzrlib,
26
without requiring a new release on every library release. Plugins should
27
also be able to use the API to export their own compatibility information
28
for code reuse between plugins.
34
An **API** is a collection of python objects/modules/packages which can be
35
used by plugins and scripts. The ``bzrlib`` **API** covers all of bzrlib,
36
but we can be more precise - e.g. the ``WorkingTree API``.
37
An **API version** is a tuple ``(major, minor, point)``.
43
For simplicity we treat API's as being compatible with a range of
44
versions: the current release of the API, and some oldest version which is
45
also compatible. While we could say that there is a set of older versions
46
with which the current version is compatible, a range is easier to
47
express, and easier for a human to look at and understand, and finally
48
easier to manage. The oldest version with which the API for a python
49
object is compatible is obtained by looking up the ``api_minimum_version``
50
attribute on the python object handed to ``require_api``, and failing that
51
the bzrlib ``api_minimum_version`` is returned. The current version of the
52
API is obtained by looking for an ``api_current_version`` attribute, and
53
if that is not found, an ``version_info`` attribute (of which the first 3
54
elements are used). If no current version can be found, the bzrlib
55
``version_info`` attribute is used to generate a current API version.
56
This lookup sequence allows users with simple setups (and no python style
57
``version_info`` tuple) to still export an API version, and for new API's
58
to be managed more granularly later on with a smooth transition -
59
everything starts off in lockstep with bzrlib's master version.
61
API versions are compared lexically to answer the question 'is
62
the requested version X <= the current version, and >= the minimum
68
The minimum API versions should be adjusted to the **oldest** API version
69
with which client code of the API will successfully run. It should not be
70
changed simply because of adding things in a compatible manner, or
71
deprecating features, but rather when errors will occur if client code is
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not updated. Versions for API's from ``bzrlib`` are given the version
73
numbers that ``bzrlib`` has had for consistency. Plugins should also take
74
this approach and use the version numbering scheme the plugin used.
79
Currently we export a single API - the ``bzrlib API`` - and no finer
80
grained APIs. The API versioning support was introduced in bzrlib 0.18.
81
For plugins or tools that want to dynamically check for the presence of
82
the API versioning API, you should compare ``bzrlib.version_info[0:3]``
85
+------------+---------------+
87
+============+===============+
88
| bzrlib | All of bzrlib |
89
+------------+---------------+
94
Some examples of using the API.
96
Requiring bzrlib 0.18 in a plugin
97
---------------------------------
99
In the plugins __init__.py::
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from bzrlib.api import require_api
103
from bzrlib.errors import IncompatibleAPI
105
require_api(bzrlib, (0, 18, 0))
106
except IncompatibleAPI:
107
raise ImportError("A bzrlib compatible with 0.18 is required.")
109
Exporting an API from a plugin
110
------------------------------
112
In the plugin ``foo`` exporting the API (in __init__.py)::
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version_info = (0, 0, 1, 'beta', 1)
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api_version = (0, 0, 1)
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In a plugin depending on that plugin (in __init__.py)::
119
import bzrlib.plugins.foo
120
from bzrlib.api import require_api
121
from bzrlib.errors import IncompatibleAPI
123
require_api(bzrlib.plugins.foo, (0, 0, 1))
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except IncompatibleAPI:
125
raise ImportError("A bzrlib compatible with 0.0.1 is required.")
added
removed
doc/developers/api-versioning.txt
