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applies to modules and classes.
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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
59
way, you need to change its name as well. For instance, if I add an optional keyword
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parameter to branch.commit - that's fine. On the other hand, if I add a
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keyword parameter to branch.commit which is a *required* transaction
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object, I should rename the API - i.e. to 'branch.commit_transaction'.
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details for you - such as updating the docstring, and issuing a warning
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when the old api is used.
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For unsupported API's, it does not hurt to follow this discipline, but its
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For unsupported API's, it does not hurt to follow this discipline, but it's
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not required. Minimally though, please try to rename things so that
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callers will at least get an AttributeError rather than weird results.
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There are some common requirements in the library: some parameters need to be
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unicode safe, some need byte strings, and so on. At the moment we have
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only codified one specific pattern: Parameters that need to be unicode
81
should be check via 'bzrlib.osutils.safe_unicode'. This will coerce the
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should be checked via ``bzrlib.osutils.safe_unicode``. This will coerce the
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input into unicode in a consistent fashion, allowing trivial strings to be
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used for programmer convenience, but not performing unpredictably in the
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presence of different locales.
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The copyright policy for bzr was recently made clear in this email (edited
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for grammatical correctness)::
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The attached patch cleans up the copyright and license statements in
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the bzr source. It also adds tests to help us remember to add them
95
with the correct text.
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We had the problem that lots of our files were "Copyright Canonical
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Development Ltd" which is not a real company, and some other variations
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on this theme. Also, some files were missing the GPL statements.
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I want to be clear about the intent of this patch, since copyright can
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be a little controversial.
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1) The big motivation for this is not to shut out the community, but
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just to clean up all of the invalid copyright statements.
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2) It has been the general policy for bzr that we want a single
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copyright holder for all of the core code. This is following the model
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set by the FSF, which makes it easier to update the code to a new
110
license in case problems are encountered. (For example, if we want to
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upgrade the project universally to GPL v3 it is much simpler if there is
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a single copyright holder). It also makes it clearer if copyright is
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ever debated, there is a single holder, which makes it easier to defend
114
in court, etc. (I think the FSF position is that if you assign them
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copyright, they can defend it in court rather than you needing to, and
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I'm sure Canonical would do the same).
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As such, Canonical has requested copyright assignments from all of the
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3) If someone wants to add code and not attribute it to Canonical, there
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is a specific list of files that are excluded from this check. And the
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test failure indicates where that is, and how to update it.
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4) If anyone feels that I changed a copyright statement incorrectly, just
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let me know, and I'll be happy to correct it. Whenever you have large
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mechanical changes like this, it is possible to make some mistakes.
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Just to reiterate, this is a community project, and it is meant to stay
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that way. Core bzr code is copyright Canonical for legal reasons, and
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the tests are just there to help us maintain that.
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may not catch every case but it's still useful sometimes.
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In some places we have variables which point to callables that construct
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new instances. That is to say, they can be used a lot like class objects,
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but they shouldn't be *named* like classes:
254
> I think that things named FooBar should create instances of FooBar when
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> called. Its plain confusing for them to do otherwise. When we have
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> something that is going to be used as a class - that is, checked for via
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> isinstance or other such idioms, them I would call it foo_class, so that
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> it is clear that a callable is not sufficient. If it is only used as a
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> factory, then yes, foo_factory is what I would use.
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Several places in Bazaar use (or will use) a registry, which is a
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mapping from names to objects or classes. The registry allows for
267
loading in registered code only when it's needed, and keeping
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associated information such as a help string or description.
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To make startup time faster, we use the ``bzrlib.lazy_import`` module to
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delay importing modules until they are actually used. ``lazy_import`` uses
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the same syntax as regular python imports. So to import a few modules in a
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from bzrlib.lazy_import import lazy_import
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lazy_import(globals(), """
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revision as _mod_revision,
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import bzrlib.transport
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At this point, all of these exist as a ``ImportReplacer`` object, ready to
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be imported once a member is accessed. Also, when importing a module into
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the local namespace, which is likely to clash with variable names, it is
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recommended to prefix it as ``_mod_<module>``. This makes it clean that
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the variable is a module, and these object should be hidden anyway, since
300
they shouldn't be imported into other namespaces.
303
Modules versus Members
304
~~~~~~~~~~~~~~~~~~~~~~
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While it is possible for ``lazy_import()`` to import members of a module
307
when using the ``from module import member`` syntax, it is recommended to
308
only use that syntax to load sub modules ``from module import submodule``.
309
This is because variables and classes can frequently be used without
310
needing a sub-member for example::
312
lazy_import(globals(), """
313
from module import MyClass
317
return isinstance(x, MyClass)
319
This will incorrectly fail, because ``MyClass`` is a ``ImportReplacer``
320
object, rather than the real class.
323
Passing to other variables
324
~~~~~~~~~~~~~~~~~~~~~~~~~~
326
It also is incorrect to assign ``ImportReplacer`` objects to other variables.
327
Because the replacer only knows about the original name, it is unable to
328
replace other variables. The ``ImportReplacer`` class will raise an
329
``IllegalUseOfScopeReplacer`` exception if it can figure out that this
330
happened. But it requires accessing a member more than once from the new
331
variable, so some bugs are not detected right away.
264
402
the command. We do this so that the library api has continual pressure
265
403
on it to be as functional as the command line in a simple manner, and
266
404
to isolate knock-on effects throughout the blackbox test suite when a
267
command changes it name or signature. Ideally only the tests for a
405
command changes its name or signature. Ideally only the tests for a
268
406
given command are affected when a given command is changed.
408
4. If you have a test which does actually require running bzr in a
409
subprocess you can use ``run_bzr_subprocess``. By default the spawned
410
process will not load plugins unless ``--allow-plugins`` is supplied.
416
We make selective use of doctests__. In general they should provide
417
*examples* within the API documentation which can incidentally be tested. We
418
don't try to test every important case using doctests -- regular Python
419
tests are generally a better solution.
421
Most of these are in ``bzrlib/doc/api``. More additions are welcome.
423
__ http://docs.python.org/lib/module-doctest.html
272
428
Currently, bzr selftest is used to invoke tests.
276
432
./bzr selftest -v blackbox
434
To skip a particular test (or set of tests), you need to use a negative
437
./bzr selftest '^(?!.*blackbox)'
279
440
Errors and exceptions
280
441
=====================
282
Errors are handled through Python exceptions. They can represent user
283
errors, environmental errors or program bugs. Sometimes we can't be sure
284
at the time it's raised which case applies. See bzrlib/errors.py for
285
details on the error-handling practices.
443
Errors are handled through Python exceptions.
445
We broadly classify errors as either being either internal or not,
446
depending on whether ``user_error`` is set or not. If we think it's our
447
fault, we show a backtrace, an invitation to report the bug, and possibly
448
other details. This is the default for errors that aren't specifically
449
recognized as being caused by a user error. Otherwise we show a briefer
450
message, unless -Derror was given.
452
Many errors originate as "environmental errors" which are raised by Python
453
or builtin libraries -- for example IOError. These are treated as being
454
our fault, unless they're caught in a particular tight scope where we know
455
that they indicate a user errors. For example if the repository format
456
is not found, the user probably gave the wrong path or URL. But if one of
457
the files inside the repository is not found, then it's our fault --
458
either there's a bug in bzr, or something complicated has gone wrong in
459
the environment that means one internal file was deleted.
461
Many errors are defined in ``bzrlib/errors.py`` but it's OK for new errors
462
to be added near the place where they are used.
464
Exceptions are formatted for the user by conversion to a string
465
(eventually calling their ``__str__`` method.) As a convenience the
466
``._fmt`` member can be used as a template which will be mapped to the
467
error's instance dict.
469
New exception classes should be defined when callers might want to catch
470
that exception specifically, or when it needs a substantially different
473
Exception strings should start with a capital letter and should not have a
474
final fullstop. If long, they may contain newlines to break the text.
344
534
the form of URL components.
537
Unicode and Encoding Support
538
============================
540
This section discusses various techniques that Bazaar uses to handle
541
characters that are outside the ASCII set.
546
When a ``Command`` object is created, it is given a member variable
547
accessible by ``self.outf``. This is a file-like object, which is bound to
548
``sys.stdout``, and should be used to write information to the screen,
549
rather than directly writing to ``sys.stdout`` or calling ``print``.
550
This file has the ability to translate Unicode objects into the correct
551
representation, based on the console encoding. Also, the class attribute
552
``encoding_type`` will effect how unprintable characters will be
553
handled. This parameter can take one of 3 values:
556
Unprintable characters will be represented with a suitable replacement
557
marker (typically '?'), and no exception will be raised. This is for
558
any command which generates text for the user to review, rather than
559
for automated processing.
560
For example: ``bzr log`` should not fail if one of the entries has text
561
that cannot be displayed.
564
Attempting to print an unprintable character will cause a UnicodeError.
565
This is for commands that are intended more as scripting support, rather
566
than plain user review.
567
For exampl: ``bzr ls`` is designed to be used with shell scripting. One
568
use would be ``bzr ls --null --unknows | xargs -0 rm``. If ``bzr``
569
printed a filename with a '?', the wrong file could be deleted. (At the
570
very least, the correct file would not be deleted). An error is used to
571
indicate that the requested action could not be performed.
574
Do not attempt to automatically convert Unicode strings. This is used
575
for commands that must handle conversion themselves.
576
For example: ``bzr diff`` needs to translate Unicode paths, but should
577
not change the exact text of the contents of the files.
580
``bzrlib.urlutils.unescape_for_display``
581
----------------------------------------
583
Because Transports work in URLs (as defined earlier), printing the raw URL
584
to the user is usually less than optimal. Characters outside the standard
585
set are printed as escapes, rather than the real character, and local
586
paths would be printed as ``file://`` urls. The function
587
``unescape_for_display`` attempts to unescape a URL, such that anything
588
that cannot be printed in the current encoding stays an escaped URL, but
589
valid characters are generated where possible.
347
592
Merge/review process
348
593
====================
350
595
If you'd like to propose a change, please post to the
351
bazaar-ng@lists.canonical.com list with a patch, bzr changeset, or link to a
596
bazaar@lists.canonical.com list with a patch, bzr changeset, or link to a
352
597
branch. Please put '[patch]' in the subject so we can pick them out, and
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598
include some text explaining the change. Remember to put an update to the NEWS
354
599
file in your diff, if it makes any changes visible to users or plugin
added
removed
HACKING
