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436 lines
13 KiB
Python
436 lines
13 KiB
Python
"""New import scheme with package support.
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Quick Reference
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---------------
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- To enable package support, execute "import ni" before importing any
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packages. Importing this module automatically installs the relevant
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import hooks.
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- To create a package named spam containing sub-modules ham, bacon and
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eggs, create a directory spam somewhere on Python's module search
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path (i.e. spam's parent directory must be one of the directories in
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sys.path or $PYTHONPATH); then create files ham.py, bacon.py and
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eggs.py inside spam.
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- To import module ham from package spam and use function hamneggs()
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from that module, you can either do
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import spam.ham # *not* "import spam" !!!
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spam.ham.hamneggs()
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or
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from spam import ham
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ham.hamneggs()
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or
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from spam.ham import hamneggs
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hamneggs()
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- Importing just "spam" does not do what you expect: it creates an
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empty package named spam if one does not already exist, but it does
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not import spam's submodules. The only submodule that is guaranteed
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to be imported is spam.__init__, if it exists. Note that
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spam.__init__ is a submodule of package spam. It can reference to
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spam's namespace via the '__.' prefix, for instance
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__.spam_inited = 1 # Set a package-level variable
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Theory of Operation
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-------------------
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A Package is a module that can contain other modules. Packages can be
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nested. Package introduce dotted names for modules, like P.Q.M, which
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could correspond to a file P/Q/M.py found somewhere on sys.path. It
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is possible to import a package itself, though this makes little sense
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unless the package contains a module called __init__.
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A package has two variables that control the namespace used for
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packages and modules, both initialized to sensible defaults the first
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time the package is referenced.
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(1) A package's *module search path*, contained in the per-package
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variable __path__, defines a list of *directories* where submodules or
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subpackages of the package are searched. It is initialized to the
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directory containing the package. Setting this variable to None makes
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the module search path default to sys.path (this is not quite the same
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as setting it to sys.path, since the latter won't track later
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assignments to sys.path).
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(2) A package's *import domain*, contained in the per-package variable
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__domain__, defines a list of *packages* that are searched (using
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their respective module search paths) to satisfy imports. It is
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initialized to the list cosisting of the package itself, its parent
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package, its parent's parent, and so on, ending with the root package
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(the nameless package containing all top-level packages and modules,
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whose module search path is None, implying sys.path).
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The default domain implements a search algorithm called "expanding
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search". An alternative search algorithm called "explicit search"
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fixes the import search path to contain only the root package,
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requiring the modules in the package to name all imported modules by
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their full name. The convention of using '__' to refer to the current
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package (both as a per-module variable and in module names) can be
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used by packages using explicit search to refer to modules in the same
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package; this combination is known as "explicit-relative search".
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The PackageImporter and PackageLoader classes together implement the
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following policies:
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- There is a root package, whose name is ''. It cannot be imported
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directly but may be referenced, e.g. by using '__' from a top-level
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module.
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- In each module or package, the variable '__' contains a reference to
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the parent package; in the root package, '__' points to itself.
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- In the name for imported modules (e.g. M in "import M" or "from M
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import ..."), a leading '__' refers to the current package (i.e.
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the package containing the current module); leading '__.__' and so
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on refer to the current package's parent, and so on. The use of
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'__' elsewhere in the module name is not supported.
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- Modules are searched using the "expanding search" algorithm by
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virtue of the default value for __domain__.
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- If A.B.C is imported, A is searched using __domain__; then
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subpackage B is searched in A using its __path__, and so on.
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- Built-in modules have priority: even if a file sys.py exists in a
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package, "import sys" imports the built-in sys module.
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- The same holds for frozen modules, for better or for worse.
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- Submodules and subpackages are not automatically loaded when their
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parent packages is loaded.
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- The construct "from package import *" is illegal. (It can still be
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used to import names from a module.)
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- When "from package import module1, module2, ..." is used, those
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modules are explicitly loaded.
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- When a package is loaded, if it has a submodule __init__, that
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module is loaded. This is the place where required submodules can
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be loaded, the __path__ variable extended, etc. The __init__ module
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is loaded even if the package was loaded only in order to create a
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stub for a sub-package: if "import P.Q.R" is the first reference to
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P, and P has a submodule __init__, P.__init__ is loaded before P.Q
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is even searched.
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Caveats:
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- It is possible to import a package that has no __init__ submodule;
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this is not particularly useful but there may be useful applications
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for it (e.g. to manipulate its search paths from the outside!).
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- There are no special provisions for os.chdir(). If you plan to use
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os.chdir() before you have imported all your modules, it is better
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not to have relative pathnames in sys.path. (This could actually be
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fixed by changing the implementation of path_join() in the hook to
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absolutize paths.)
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- Packages and modules are introduced in sys.modules as soon as their
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loading is started. When the loading is terminated by an exception,
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the sys.modules entries remain around.
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- There are no special measures to support mutually recursive modules,
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but it will work under the same conditions where it works in the
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flat module space system.
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- Sometimes dummy entries (whose value is None) are entered in
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sys.modules, to indicate that a particular module does not exist --
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this is done to speed up the expanding search algorithm when a
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module residing at a higher level is repeatedly imported (Python
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promises that importing a previously imported module is cheap!)
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- Although dynamically loaded extensions are allowed inside packages,
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the current implementation (hardcoded in the interpreter) of their
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initialization may cause problems if an extension invokes the
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interpreter during its initialization.
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- reload() may find another version of the module only if it occurs on
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the package search path. Thus, it keeps the connection to the
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package to which the module belongs, but may find a different file.
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XXX Need to have an explicit name for '', e.g. '__root__'.
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"""
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import imp
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import string
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import sys
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import __builtin__
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import ihooks
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from ihooks import ModuleLoader, ModuleImporter
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class PackageLoader(ModuleLoader):
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"""A subclass of ModuleLoader with package support.
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find_module_in_dir() will succeed if there's a subdirectory with
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the given name; load_module() will create a stub for a package and
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load its __init__ module if it exists.
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"""
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def find_module_in_dir(self, name, dir):
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if dir is not None:
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dirname = self.hooks.path_join(dir, name)
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if self.hooks.path_isdir(dirname):
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return None, dirname, ('', '', 'PACKAGE')
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return ModuleLoader.find_module_in_dir(self, name, dir)
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def load_module(self, name, stuff):
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file, filename, info = stuff
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suff, mode, type = info
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if type == 'PACKAGE':
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return self.load_package(name, stuff)
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if sys.modules.has_key(name):
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m = sys.modules[name]
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else:
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sys.modules[name] = m = imp.new_module(name)
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self.set_parent(m)
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if type == imp.C_EXTENSION and '.' in name:
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return self.load_dynamic(name, stuff)
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else:
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return ModuleLoader.load_module(self, name, stuff)
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def load_dynamic(self, name, stuff):
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file, filename, (suff, mode, type) = stuff
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# Hack around restriction in imp.load_dynamic()
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i = string.rfind(name, '.')
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tail = name[i+1:]
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if sys.modules.has_key(tail):
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save = sys.modules[tail]
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else:
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save = None
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sys.modules[tail] = imp.new_module(name)
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try:
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m = imp.load_dynamic(tail, filename, file)
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finally:
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if save:
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sys.modules[tail] = save
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else:
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del sys.modules[tail]
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sys.modules[name] = m
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return m
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def load_package(self, name, stuff):
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file, filename, info = stuff
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if sys.modules.has_key(name):
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package = sys.modules[name]
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else:
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sys.modules[name] = package = imp.new_module(name)
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package.__path__ = [filename]
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self.init_package(package)
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return package
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def init_package(self, package):
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self.set_parent(package)
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self.set_domain(package)
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self.call_init_module(package)
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def set_parent(self, m):
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name = m.__name__
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if '.' in name:
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name = name[:string.rfind(name, '.')]
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else:
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name = ''
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m.__ = sys.modules[name]
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def set_domain(self, package):
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name = package.__name__
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package.__domain__ = domain = [name]
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while '.' in name:
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name = name[:string.rfind(name, '.')]
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domain.append(name)
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if name:
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domain.append('')
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def call_init_module(self, package):
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stuff = self.find_module('__init__', package.__path__)
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if stuff:
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m = self.load_module(package.__name__ + '.__init__', stuff)
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package.__init__ = m
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class PackageImporter(ModuleImporter):
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"""Importer that understands packages and '__'."""
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def __init__(self, loader = None, verbose = 0):
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ModuleImporter.__init__(self,
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loader or PackageLoader(None, verbose), verbose)
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def import_module(self, name, globals={}, locals={}, fromlist=[]):
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if globals.has_key('__'):
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package = globals['__']
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else:
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# No calling context, assume in root package
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package = sys.modules['']
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if name[:3] in ('__.', '__'):
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p = package
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name = name[3:]
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while name[:3] in ('__.', '__'):
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p = p.__
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name = name[3:]
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if not name:
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return self.finish(package, p, '', fromlist)
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if '.' in name:
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i = string.find(name, '.')
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name, tail = name[:i], name[i:]
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else:
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tail = ''
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mname = p.__name__ and p.__name__+'.'+name or name
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m = self.get1(mname)
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return self.finish(package, m, tail, fromlist)
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if '.' in name:
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i = string.find(name, '.')
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name, tail = name[:i], name[i:]
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else:
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tail = ''
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for pname in package.__domain__:
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mname = pname and pname+'.'+name or name
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m = self.get0(mname)
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if m: break
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else:
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raise ImportError, "No such module %s" % name
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return self.finish(m, m, tail, fromlist)
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def finish(self, module, m, tail, fromlist):
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# Got ....A; now get ....A.B.C.D
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yname = m.__name__
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if tail and sys.modules.has_key(yname + tail): # Fast path
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yname, tail = yname + tail, ''
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m = self.get1(yname)
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while tail:
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i = string.find(tail, '.', 1)
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if i > 0:
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head, tail = tail[:i], tail[i:]
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else:
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head, tail = tail, ''
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yname = yname + head
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m = self.get1(yname)
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# Got ....A.B.C.D; now finalize things depending on fromlist
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if not fromlist:
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return module
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if '__' in fromlist:
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raise ImportError, "Can't import __ from anywhere"
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if not hasattr(m, '__path__'): return m
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if '*' in fromlist:
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raise ImportError, "Can't import * from a package"
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for f in fromlist:
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if hasattr(m, f): continue
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fname = yname + '.' + f
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self.get1(fname)
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return m
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def get1(self, name):
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m = self.get(name)
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if not m:
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raise ImportError, "No module named %s" % name
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return m
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def get0(self, name):
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m = self.get(name)
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if not m:
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sys.modules[name] = None
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return m
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def get(self, name):
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# Internal routine to get or load a module when its parent exists
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if sys.modules.has_key(name):
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return sys.modules[name]
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if '.' in name:
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i = string.rfind(name, '.')
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head, tail = name[:i], name[i+1:]
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else:
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head, tail = '', name
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path = sys.modules[head].__path__
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stuff = self.loader.find_module(tail, path)
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if not stuff:
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return None
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sys.modules[name] = m = self.loader.load_module(name, stuff)
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if head:
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setattr(sys.modules[head], tail, m)
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return m
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def reload(self, module):
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name = module.__name__
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if '.' in name:
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i = string.rfind(name, '.')
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head, tail = name[:i], name[i+1:]
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path = sys.modules[head].__path__
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else:
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tail = name
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path = sys.modules[''].__path__
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stuff = self.loader.find_module(tail, path)
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if not stuff:
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raise ImportError, "No module named %s" % name
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return self.loader.load_module(name, stuff)
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def unload(self, module):
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if hasattr(module, '__path__'):
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raise ImportError, "don't know how to unload packages yet"
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PackageImporter.unload(self, module)
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def install(self):
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if not sys.modules.has_key(''):
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sys.modules[''] = package = imp.new_module('')
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package.__path__ = None
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self.loader.init_package(package)
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for m in sys.modules.values():
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if not m: continue
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if not hasattr(m, '__'):
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self.loader.set_parent(m)
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ModuleImporter.install(self)
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def install(v = 0):
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ihooks.install(PackageImporter(None, v))
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def uninstall():
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ihooks.uninstall()
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def ni(v = 0):
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install(v)
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def no():
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uninstall()
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def test():
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import pdb
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try:
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testproper()
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except:
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sys.last_type, sys.last_value, sys.last_traceback = (
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sys.exc_type, sys.exc_value, sys.exc_traceback)
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print
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print sys.last_type, ':', sys.last_value
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print
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pdb.pm()
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def testproper():
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install(1)
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try:
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import mactest
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print dir(mactest)
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raw_input('OK?')
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finally:
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uninstall()
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if __name__ == '__main__':
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test()
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else:
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install()
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