Ignore changes in the amount of whitespace
Differences between version dated 2007-08-11 07:06:02 and 2010-08-23 16:16:08
(spanning 4 versions)
Deletions are marked like this.
Additions are marked like this.
Dynamic, Lazy, and Weak Imports with the ``Importing`` Toolkit
==============================================================
NEW in 1.10: ``@whenImported`` can now be used as a decorator for lazy imports
Need to import an object when all you've got is its name? Need to lazily
import modules, such that they don't actually get loaded until you use them?
Want to have some code in a module that only gets run *if* another module is
If `string_or_sequence` is not a string but is iterable, this returns a
list created by calling ``importObject()`` on each element of the sequence.
Note that you could view this as always using importObject; it just takes
advantage of the knowledge that string.split() will always return a list
of strings, rather than arbitrary objects.
importSuite(name_or_sequence [, globalDict])
Convert a string or sequence to a ``unittest.TestSuite``
with normal imports of the targeted module(s), whether they are lazily loaded
before or after the normal imports.)
Question -- could lazyModule and whenImported be added the the standard library?
I would like to be rid of the function-internal imports, but I would also like to
be able to add aspects (such as logging) to the stdlib without adding run-time
slowdowns when they aren't used. -jJ
lazyModule(moduleName)
Return module `moduleName`, but with its contents loaded "on demand"
Example usage::
sdist = lazyModule('distutils.commands.sdist')
sdist = lazyModule('distutils.command.sdist')
This is roughly equivalent to ``import distutils.commands.sdist as sdist``,
This is roughly equivalent to ``import distutils.command.sdist as sdist``,
except that the real import doesn't take place until/unless you try to
access some attribute of the ``sdist`` object -- unless of course the
module was already imported before the above line was executed.
the callback will be invoked only as soon as the third-party module is *used*
(i.e. any of its attributes are accessed), and not a moment before.
whenImported(moduleName, callback)
Call ``callback(module)`` when module named `moduleName` is first used
@whenImported(moduleName)
Call ``func(module)`` when module named `moduleName` is first used
`moduleName` must be a fully qualified (i.e. absolute) module name.
`callback` must accept one argument: the module object named by
`moduleName`. `moduleName` must be a fully qualified (i.e. absolute)
module name. The callback **must not allow any unhandled exceptions to
escape**, or it may prevent other registered callbacks from running.
If the named module has already been loaded, ``callback(module)`` is
called immediately, and the module object is returned from this function.
If the module has not been imported, or has only been imported lazily,
then the callback is invoked when the module is first *used*, and a lazy
import of the module is returned from this function.
If the module was imported lazily and used before calling this function,
the hook is called immediately, and the loaded module is returned from this
function.
Note that using this function implies a possible lazy import of the
specified module, and lazy importing means that any 'ImportError' will be
deferred until the module is used.
If the named module has already been loaded, the decorated function
is called immediately. If the named module is not yet loaded, the
decorated function is registered as a callback that will be invoked
when the named module is actually used.
In either case, the decorated function will be passed one argument:
the module object named by `moduleName`. It **must not allow any
unhandled exceptions to escape**, or it may prevent other registered
callbacks from running.
Using this function implies a possible lazy import of the specified module,
and lazy importing means that any ``ImportError`` will be deferred until
the module is actually used.
(Note: in older versions of the Importing toolkit, this function actually
took a second argument: the callback to be registered or called. If you
use it in this fashion, the return value is not the decorated function, but
is instead the module object or lazy module object named by `moduleName`.)
Deprecated Features
Please direct questions regarding this package to the PEAK mailing list; see
http://www.eby-sarna.com/mailman/listinfo/PEAK/ for details.
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