20
30
function runs. Import statements have a cost, so try to make sure
21
31
they don't run inside hot functions.
23
* Please write PEP-8__ compliant code.
25
One often-missed requirement is that the first line of docstrings
26
should be a self-contained one-sentence summary.
28
__ http://www.python.org/peps/pep-0008.html
30
33
* Module names should always be given fully-qualified,
31
34
i.e. ``bzrlib.hashcache`` not just ``hashcache``.
36
* Commands should return non-zero when they encounter circumstances that
37
the user should really pay attention to - which includes trivial shell
40
Recommended values are
42
1. Conflicts in merge-like operations, or changes are present in
44
2. Unrepresentable diff changes (i.e. binary files that we cannot show
46
3. An error or exception has occurred.
51
We have a commitment to 6 months API stability - any supported symbol in a
52
release of bzr MUST NOT be altered in any way that would result in
53
breaking existing code that uses it. That means that method names,
54
parameter ordering, parameter names, variable and attribute names etc must
55
not be changed without leaving a 'deprecated forwarder' behind. This even
56
applies to modules and classes.
58
If you wish to change the behaviour of a supported API in an incompatible
59
way, you need to change its name as well. For instance, if I add a optional keyword
60
parameter to branch.commit - that's fine. On the other hand, if I add a
61
keyword parameter to branch.commit which is a *required* transaction
62
object, I should rename the API - i.e. to 'branch.commit_transaction'.
64
When renaming such supported API's, be sure to leave a deprecated_method (or
65
_function or ...) behind which forwards to the new API. See the
66
bzrlib.symbol_versioning module for decorators that take care of the
67
details for you - such as updating the docstring, and issuing a warning
68
when the old api is used.
70
For unsupported API's, it does not hurt to follow this discipline, but its
71
not required. Minimally though, please try to rename things so that
72
callers will at least get an AttributeError rather than weird results.
75
Standard parameter types
76
------------------------
78
There are some common requirements in the library: some parameters need to be
79
unicode safe, some need byte strings, and so on. At the moment we have
80
only codified one specific pattern: Parameters that need to be unicode
81
should be check via 'bzrlib.osutils.safe_unicode'. This will coerce the
82
input into unicode in a consistent fashion, allowing trivial strings to be
83
used for programmer convenience, but not performing unpredictably in the
84
presence of different locales.
45
99
bugs should be listed. See the existing entries for an idea of what
102
Within each release, entries in the news file should have the most
103
user-visible changes first. So the order should be approximately:
105
* changes to existing behaviour - the highest priority because the
106
user's existing knowledge is incorrect
107
* new features - should be brought to their attention
108
* bug fixes - may be of interest if the bug was affecting them, and
109
should include the bug number if any
110
* major documentation changes
111
* changes to internal interfaces
113
People who made significant contributions to each change are listed in
114
parenthesis. This can include reporting bugs (particularly with good
115
details or reproduction recipes), submitting patches, etc.
120
Functions, methods, classes and modules should have docstrings
121
describing how they are used.
123
The first line of the docstring should be a self-contained sentence.
125
For the special case of Command classes, this acts as the user-visible
126
documentation shown by the help command.
128
The docstrings should be formatted as reStructuredText_ (like this
129
document), suitable for processing using the epydoc_ tool into HTML
132
.. _reStructuredText: http://docutils.sourceforge.net/rst.html
133
.. _epydoc: http://epydoc.sourceforge.net/
140
Please write PEP-8__ compliant code.
142
One often-missed requirement is that the first line of docstrings
143
should be a self-contained one-sentence summary.
145
__ http://www.python.org/peps/pep-0008.html
152
Functions, methods or members that are in some sense "private" are given
153
a leading underscore prefix. This is just a hint that code outside the
154
implementation should probably not use that interface.
156
We prefer class names to be concatenated capital words (``TestCase``)
157
and variables, methods and functions to be lowercase words joined by
158
underscores (``revision_id``, ``get_revision``).
160
For the purposes of naming some names are treated as single compound
161
words: "filename", "revno".
163
Consider naming classes as nouns and functions/methods as verbs.
169
``revision_id`` not ``rev_id`` or ``revid``
171
Functions that transform one thing to another should be named ``x_to_y``
172
(not ``x2y`` as occurs in some old code.)
178
Python destructors (``__del__``) work differently to those of other
179
languages. In particular, bear in mind that destructors may be called
180
immediately when the object apparently becomes unreferenced, or at some
181
later time, or possibly never at all. Therefore we have restrictions on
182
what can be done inside them.
184
0. Never use a __del__ method without asking Martin/Robert first.
186
1. Never rely on a ``__del__`` method running. If there is code that
187
must run, do it from a ``finally`` block instead.
189
2. Never ``import`` from inside a ``__del__`` method, or you may crash the
192
3. In some places we raise a warning from the destructor if the object
193
has not been cleaned up or closed. This is considered OK: the warning
194
may not catch every case but it's still useful sometimes.
200
In some places we have variables which point to callables that construct
201
new instances. That is to say, they can be used a lot like class objects,
202
but they shouldn't be *named* like classes:
204
> I think that things named FooBar should create instances of FooBar when
205
> called. Its plain confusing for them to do otherwise. When we have
206
> something that is going to be used as a class - that is, checked for via
207
> isinstance or other such idioms, them I would call it foo_class, so that
208
> it is clear that a callable is not sufficient. If it is only used as a
209
> factory, then yes, foo_factory is what I would use.
215
To make startup time faster, we use the ``bzrlib.lazy_import`` module to
216
delay importing modules until they are actually used. ``lazy_import`` uses
217
the same syntax as regular python imports. So to import a few modules in a
220
from bzrlib.lazy_import import lazy_import
221
lazy_import(globals(), """
232
import bzrlib.transport
236
At this point, all of these exist as a ``ImportReplacer`` object, ready to
237
be imported once a member is accessed.
240
Modules versus Members
241
~~~~~~~~~~~~~~~~~~~~~~
243
While it is possible for ``lazy_import()`` to import members of a module
244
wehn using the ``from module import member`` syntax, it is recommended to
245
only use that syntax to load sub modules ``from module import submodule``.
246
This is because variables and classes can frequently be used without
247
needing a sub-member for example::
249
lazy_import(globals(), """
250
from module import MyClass
254
return isinstance(x, MyClass)
256
This will incorrectly fail, because ``MyClass`` is a ``ImportReplacer``
257
object, rather than the real class.
260
Passing to other variables
261
~~~~~~~~~~~~~~~~~~~~~~~~~~
263
It also is incorrect to assign ``ImportReplacer`` objects to other variables.
264
Because the replacer only knows about the original name, it is unable to
265
replace other variables. The ``ImportReplacer`` class will raise an
266
``IllegalUseOfScopeReplacer`` exception if it can figure out that this
267
happened. But it requires accessing a member more than once from the new
268
variable, so some bugs are not detected right away.
90
312
tests subdirectory under the package being tested.
92
314
For example, tests for merge3 in bzrlib belong in bzrlib/tests/test_merge3.py.
315
See bzrlib/selftest/test_sampler.py for a template test script.
317
Tests can be written for the UI or for individual areas of the library.
318
Choose whichever is appropriate: if adding a new command, or a new command
319
option, then you should be writing a UI test. If you are both adding UI
320
functionality and library functionality, you will want to write tests for
321
both the UI and the core behaviours. We call UI tests 'blackbox' tests
322
and they are found in ``bzrlib/tests/blackbox/*.py``.
324
When writing blackbox tests please honour the following conventions:
326
1. Place the tests for the command 'name' in
327
bzrlib/tests/blackbox/test_name.py. This makes it easy for developers
328
to locate the test script for a faulty command.
330
2. Use the 'self.run_bzr("name")' utility function to invoke the command
331
rather than running bzr in a subprocess or invoking the
332
cmd_object.run() method directly. This is a lot faster than
333
subprocesses and generates the same logging output as running it in a
334
subprocess (which invoking the method directly does not).
336
3. Only test the one command in a single test script. Use the bzrlib
337
library when setting up tests and when evaluating the side-effects of
338
the command. We do this so that the library api has continual pressure
339
on it to be as functional as the command line in a simple manner, and
340
to isolate knock-on effects throughout the blackbox test suite when a
341
command changes it name or signature. Ideally only the tests for a
342
given command are affected when a given command is changed.
347
We make selective use of doctests__. In general they should provide
348
*examples* within the API documentation which can incidentally be tested. We
349
don't try to test every important case using doctests -- regular Python
350
tests are generally a better solution.
352
Most of these are in ``bzrlib/doc/api``. More additions are welcome.
354
__ http://docs.python.org/lib/module-doctest.html
96
359
Currently, bzr selftest is used to invoke tests.
97
360
You can provide a pattern argument to run a subset. For example,
98
to run just the whitebox tests, run bzr selftest --pattern .*whitebox.*
361
to run just the blackbox tests, run::
363
./bzr selftest -v blackbox
365
To skip a particular test (or set of tests), you need to use a negative
368
./bzr selftest '^(?!.*blackbox)'
371
Errors and exceptions
372
=====================
374
Errors are handled through Python exceptions. They can represent user
375
errors, environmental errors or program bugs. Sometimes we can't be sure
376
at the time it's raised which case applies. See bzrlib/errors.py for
377
details on the error-handling practices.
384
Integer identifier for a revision on the main line of a branch.
385
Revision 0 is always the null revision; others are 1-based
386
indexes into the branch's revision history.
392
The ``Transport`` layer handles access to local or remote directories.
393
Each Transport object acts like a logical connection to a particular
394
directory, and it allows various operations on files within it. You can
395
*clone* a transport to get a new Transport connected to a subdirectory or
398
Transports are not used for access to the working tree. At present
399
working trees are always local and they are accessed through the regular
400
Python file io mechanisms.
405
Transports work in URLs. Take note that URLs are by definition only
406
ASCII - the decision of how to encode a Unicode string into a URL must be
407
taken at a higher level, typically in the Store. (Note that Stores also
408
escape filenames which cannot be safely stored on all filesystems, but
409
this is a different level.)
411
The main reason for this is that it's not possible to safely roundtrip a
412
URL into Unicode and then back into the same URL. The URL standard
413
gives a way to represent non-ASCII bytes in ASCII (as %-escapes), but
414
doesn't say how those bytes represent non-ASCII characters. (They're not
415
guaranteed to be UTF-8 -- that is common but doesn't happen everywhere.)
417
For example if the user enters the url ``http://example/%e0`` there's no
418
way to tell whether that character represents "latin small letter a with
419
grave" in iso-8859-1, or "latin small letter r with acute" in iso-8859-2
420
or malformed UTF-8. So we can't convert their URL to Unicode reliably.
422
Equally problematic if we're given a url-like string containing non-ascii
423
characters (such as the accented a) we can't be sure how to convert that
424
to the correct URL, because we don't know what encoding the server expects
425
for those characters. (Although this is not totally reliable we might still
426
accept these and assume they should be put into UTF-8.)
428
A similar edge case is that the url ``http://foo/sweet%2Fsour`` contains
429
one directory component whose name is "sweet/sour". The escaped slash is
430
not a directory separator. If we try to convert URLs to regular Unicode
431
paths this information will be lost.
433
This implies that Transports must natively deal with URLs; for simplicity
434
they *only* deal with URLs and conversion of other strings to URLs is done
435
elsewhere. Information they return, such as from ``list_dir``, is also in
436
the form of URL components.
439
Unicode and Encoding Support
440
============================
442
This section discusses various techniques that Bazaar uses to handle
443
characters that are outside the ASCII set.
448
When a ``Command`` object is created, it is given a member variable
449
accessible by ``self.outf``. This is a file-like object, which is bound to
450
``sys.stdout``, and should be used to write information to the screen,
451
rather than directly writing to ``sys.stdout`` or calling ``print``.
452
This file has the ability to translate Unicode objects into the correct
453
representation, based on the console encoding. Also, the class attribute
454
``encoding_type`` will effect how unprintable characters will be
455
handled. This parameter can take one of 3 values:
458
Unprintable characters will be represented with a suitable replacement
459
marker (typically '?'), and no exception will be raised. This is for
460
any command which generates text for the user to review, rather than
461
for automated processing.
462
For example: ``bzr log`` should not fail if one of the entries has text
463
that cannot be displayed.
466
Attempting to print and unprintable character will cause a UnicodeError.
467
This is for commands that are intended more as scripting support, rather
468
than plain user review.
469
For exampl: ``bzr ls`` is designed to be used with shell scripting. One
470
use would be ``bzr ls --null --unknows | xargs -0 rm``. If ``bzr``
471
printed a filename with a '?', the wrong file could be deleted. (At the
472
very least, the correct file would not be deleted). An error is used to
473
indicate that the requested action could not be performed.
476
Do not attempt to automatically convert Unicode strings. This is used
477
for commands that must handle conversion themselves.
478
For example: ``bzr diff`` needs to translate Unicode paths, but should
479
not change the exact text of the contents of the files.
482
``bzrlib.urlutils.unescape_for_display``
483
----------------------------------------
485
Because Transports work in URLs (as defined earlier), printing the raw URL
486
to the user is usually less than optimal. Characters outside the standard
487
set are printed as escapes, rather than the real character, and local
488
paths would be printed as ``file://`` urls. The function
489
``unescape_for_display`` attempts to unescape a URL, such that anything
490
that cannot be printed in the current encoding stays an escaped URL, but
491
valid characters are generated where possible.
497
If you'd like to propose a change, please post to the
498
bazaar-ng@lists.canonical.com list with a patch, bzr changeset, or link to a
499
branch. Please put '[patch]' in the subject so we can pick them out, and
500
include some text explaining the change. Remember to put an update to the NEWS
501
file in your diff, if it makes any changes visible to users or plugin
502
developers. Please include a diff against mainline if you're giving a link to
505
Please indicate if you think the code is ready to merge, or if it's just a
506
draft or for discussion. If you want comments from many developers rather than
507
to be merged, you can put '[rfc]' in the subject lines.
509
Anyone is welcome to review code. There are broadly three gates for
512
* Doesn't reduce test coverage: if it adds new methods or commands,
513
there should be tests for them. There is a good test framework
514
and plenty of examples to crib from, but if you are having trouble
515
working out how to test something feel free to post a draft patch
518
* Doesn't reduce design clarity, such as by entangling objects
519
we're trying to separate. This is mostly something the more
520
experienced reviewers need to help check.
522
* Improves bugs, features, speed, or code simplicity.
524
Code that goes in should pass all three.
526
If you read a patch please reply and say so. We can use a numeric scale
527
of -1, -0, +0, +1, meaning respectively "really don't want it in current
528
form", "somewhat uncomfortable", "ok with me", and "please put it in".
529
Anyone can "vote". (It's not really voting, just a terse expression.)
531
If something gets say two +1 votes from core reviewers, and no
532
vetos, then it's OK to come in. Any of the core developers can bring it
533
into their integration branch, which I'll merge regularly. (If you do
534
so, please reply and say so.)
537
Making installers for OS Windows
538
================================
539
To build a win32 installer, see the instructions on the wiki page:
540
http://bazaar-vcs.org/BzrWin32Installer
543
:: vim: ft=rst tw=74 ai
added
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HACKING
