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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
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way, you need to change its name as well. For instance, if I add an optional keyword
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way, you need to change its name as well. For instance, if I add a 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 it's
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For unsupported API's, it does not hurt to follow this discipline, but its
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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
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should be checked via ``bzrlib.osutils.safe_unicode``. This will coerce the
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should be check 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
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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
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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
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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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> 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
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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
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they shouldn't be imported into other namespaces.
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Modules versus Members
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~~~~~~~~~~~~~~~~~~~~~~
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While it is possible for ``lazy_import()`` to import members of a module
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when using the ``from module import member`` syntax, it is recommended to
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only use that syntax to load sub modules ``from module import submodule``.
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This is because variables and classes can frequently be used without
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needing a sub-member for example::
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lazy_import(globals(), """
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from module import MyClass
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return isinstance(x, MyClass)
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This will incorrectly fail, because ``MyClass`` is a ``ImportReplacer``
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object, rather than the real class.
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Passing to other variables
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~~~~~~~~~~~~~~~~~~~~~~~~~~
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It also is incorrect to assign ``ImportReplacer`` objects to other variables.
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Because the replacer only knows about the original name, it is unable to
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replace other variables. The ``ImportReplacer`` class will raise an
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``IllegalUseOfScopeReplacer`` exception if it can figure out that this
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happened. But it requires accessing a member more than once from the new
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variable, so some bugs are not detected right away.
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the command. We do this so that the library api has continual pressure
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on it to be as functional as the command line in a simple manner, and
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to isolate knock-on effects throughout the blackbox test suite when a
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command changes its name or signature. Ideally only the tests for a
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command changes it name or signature. Ideally only the tests for a
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given command are affected when a given command is changed.
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4. If you have a test which does actually require running bzr in a
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subprocess you can use ``run_bzr_subprocess``. By default the spawned
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process will not load plugins unless ``--allow-plugins`` is supplied.
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Errors and exceptions
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=====================
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Errors are handled through Python exceptions.
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We broadly classify errors as either being either internal or not,
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depending on whether ``user_error`` is set or not. If we think it's our
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fault, we show a backtrace, an invitation to report the bug, and possibly
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other details. This is the default for errors that aren't specifically
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recognized as being caused by a user error. Otherwise we show a briefer
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message, unless -Derror was given.
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Many errors originate as "environmental errors" which are raised by Python
450
or builtin libraries -- for example IOError. These are treated as being
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our fault, unless they're caught in a particular tight scope where we know
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that they indicate a user errors. For example if the repository format
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is not found, the user probably gave the wrong path or URL. But if one of
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the files inside the repository is not found, then it's our fault --
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either there's a bug in bzr, or something complicated has gone wrong in
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the environment that means one internal file was deleted.
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Many errors are defined in ``bzrlib/errors.py`` but it's OK for new errors
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to be added near the place where they are used.
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Exceptions are formatted for the user by conversion to a string
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(eventually calling their ``__str__`` method.) As a convenience the
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``._fmt`` member can be used as a template which will be mapped to the
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error's instance dict.
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New exception classes should be defined when callers might want to catch
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that exception specifically, or when it needs a substantially different
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Exception strings should start with a capital letter and should not have a
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final fullstop. If long, they may contain newlines to break the text.
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Errors are handled through Python exceptions. They can represent user
316
errors, environmental errors or program bugs. Sometimes we can't be sure
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at the time it's raised which case applies. See bzrlib/errors.py for
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details on the error-handling practices.
added
removed
HACKING
