You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
412 lines
15 KiB
412 lines
15 KiB
:mod:`imp` --- Access the :ref:`import <importsystem>` internals
|
|
================================================================
|
|
|
|
.. module:: imp
|
|
:synopsis: Access the implementation of the import statement.
|
|
:deprecated:
|
|
|
|
**Source code:** :source:`Lib/imp.py`
|
|
|
|
.. deprecated:: 3.4
|
|
The :mod:`imp` module is deprecated in favor of :mod:`importlib`.
|
|
|
|
.. index:: statement: import
|
|
|
|
--------------
|
|
|
|
This module provides an interface to the mechanisms used to implement the
|
|
:keyword:`import` statement. It defines the following constants and functions:
|
|
|
|
|
|
.. function:: get_magic()
|
|
|
|
.. index:: pair: file; byte-code
|
|
|
|
Return the magic string value used to recognize byte-compiled code files
|
|
(:file:`.pyc` files). (This value may be different for each Python version.)
|
|
|
|
.. deprecated:: 3.4
|
|
Use :attr:`importlib.util.MAGIC_NUMBER` instead.
|
|
|
|
|
|
.. function:: get_suffixes()
|
|
|
|
Return a list of 3-element tuples, each describing a particular type of
|
|
module. Each triple has the form ``(suffix, mode, type)``, where *suffix* is
|
|
a string to be appended to the module name to form the filename to search
|
|
for, *mode* is the mode string to pass to the built-in :func:`open` function
|
|
to open the file (this can be ``'r'`` for text files or ``'rb'`` for binary
|
|
files), and *type* is the file type, which has one of the values
|
|
:const:`PY_SOURCE`, :const:`PY_COMPILED`, or :const:`C_EXTENSION`, described
|
|
below.
|
|
|
|
.. deprecated:: 3.3
|
|
Use the constants defined on :mod:`importlib.machinery` instead.
|
|
|
|
|
|
.. function:: find_module(name[, path])
|
|
|
|
Try to find the module *name*. If *path* is omitted or ``None``, the list of
|
|
directory names given by ``sys.path`` is searched, but first a few special
|
|
places are searched: the function tries to find a built-in module with the
|
|
given name (:const:`C_BUILTIN`), then a frozen module (:const:`PY_FROZEN`),
|
|
and on some systems some other places are looked in as well (on Windows, it
|
|
looks in the registry which may point to a specific file).
|
|
|
|
Otherwise, *path* must be a list of directory names; each directory is
|
|
searched for files with any of the suffixes returned by :func:`get_suffixes`
|
|
above. Invalid names in the list are silently ignored (but all list items
|
|
must be strings).
|
|
|
|
If search is successful, the return value is a 3-element tuple ``(file,
|
|
pathname, description)``:
|
|
|
|
*file* is an open :term:`file object` positioned at the beginning, *pathname*
|
|
is the pathname of the file found, and *description* is a 3-element tuple as
|
|
contained in the list returned by :func:`get_suffixes` describing the kind of
|
|
module found.
|
|
|
|
If the module is built-in or frozen then *file* and *pathname* are both ``None``
|
|
and the *description* tuple contains empty strings for its suffix and mode;
|
|
the module type is indicated as given in parentheses above. If the search
|
|
is unsuccessful, :exc:`ImportError` is raised. Other exceptions indicate
|
|
problems with the arguments or environment.
|
|
|
|
If the module is a package, *file* is ``None``, *pathname* is the package
|
|
path and the last item in the *description* tuple is :const:`PKG_DIRECTORY`.
|
|
|
|
This function does not handle hierarchical module names (names containing
|
|
dots). In order to find *P.M*, that is, submodule *M* of package *P*, use
|
|
:func:`find_module` and :func:`load_module` to find and load package *P*, and
|
|
then use :func:`find_module` with the *path* argument set to ``P.__path__``.
|
|
When *P* itself has a dotted name, apply this recipe recursively.
|
|
|
|
.. deprecated:: 3.3
|
|
Use :func:`importlib.util.find_spec` instead unless Python 3.3
|
|
compatibility is required, in which case use
|
|
:func:`importlib.find_loader`. For example usage of the former case,
|
|
see the :ref:`importlib-examples` section of the :mod:`importlib`
|
|
documentation.
|
|
|
|
|
|
.. function:: load_module(name, file, pathname, description)
|
|
|
|
Load a module that was previously found by :func:`find_module` (or by an
|
|
otherwise conducted search yielding compatible results). This function does
|
|
more than importing the module: if the module was already imported, it will
|
|
reload the module! The *name* argument indicates the full
|
|
module name (including the package name, if this is a submodule of a
|
|
package). The *file* argument is an open file, and *pathname* is the
|
|
corresponding file name; these can be ``None`` and ``''``, respectively, when
|
|
the module is a package or not being loaded from a file. The *description*
|
|
argument is a tuple, as would be returned by :func:`get_suffixes`, describing
|
|
what kind of module must be loaded.
|
|
|
|
If the load is successful, the return value is the module object; otherwise,
|
|
an exception (usually :exc:`ImportError`) is raised.
|
|
|
|
**Important:** the caller is responsible for closing the *file* argument, if
|
|
it was not ``None``, even when an exception is raised. This is best done
|
|
using a :keyword:`try` ... :keyword:`finally` statement.
|
|
|
|
.. deprecated:: 3.3
|
|
If previously used in conjunction with :func:`imp.find_module` then
|
|
consider using :func:`importlib.import_module`, otherwise use the loader
|
|
returned by the replacement you chose for :func:`imp.find_module`. If you
|
|
called :func:`imp.load_module` and related functions directly with file
|
|
path arguments then use a combination of
|
|
:func:`importlib.util.spec_from_file_location` and
|
|
:func:`importlib.util.module_from_spec`. See the :ref:`importlib-examples`
|
|
section of the :mod:`importlib` documentation for details of the various
|
|
approaches.
|
|
|
|
|
|
.. function:: new_module(name)
|
|
|
|
Return a new empty module object called *name*. This object is *not* inserted
|
|
in ``sys.modules``.
|
|
|
|
.. deprecated:: 3.4
|
|
Use :func:`importlib.util.module_from_spec` instead.
|
|
|
|
|
|
.. function:: reload(module)
|
|
|
|
Reload a previously imported *module*. The argument must be a module object, so
|
|
it must have been successfully imported before. This is useful if you have
|
|
edited the module source file using an external editor and want to try out the
|
|
new version without leaving the Python interpreter. The return value is the
|
|
module object (the same as the *module* argument).
|
|
|
|
When ``reload(module)`` is executed:
|
|
|
|
* Python modules' code is recompiled and the module-level code reexecuted,
|
|
defining a new set of objects which are bound to names in the module's
|
|
dictionary. The ``init`` function of extension modules is not called a second
|
|
time.
|
|
|
|
* As with all other objects in Python the old objects are only reclaimed after
|
|
their reference counts drop to zero.
|
|
|
|
* The names in the module namespace are updated to point to any new or changed
|
|
objects.
|
|
|
|
* Other references to the old objects (such as names external to the module) are
|
|
not rebound to refer to the new objects and must be updated in each namespace
|
|
where they occur if that is desired.
|
|
|
|
There are a number of other caveats:
|
|
|
|
When a module is reloaded, its dictionary (containing the module's global
|
|
variables) is retained. Redefinitions of names will override the old
|
|
definitions, so this is generally not a problem. If the new version of a module
|
|
does not define a name that was defined by the old version, the old definition
|
|
remains. This feature can be used to the module's advantage if it maintains a
|
|
global table or cache of objects --- with a :keyword:`try` statement it can test
|
|
for the table's presence and skip its initialization if desired::
|
|
|
|
try:
|
|
cache
|
|
except NameError:
|
|
cache = {}
|
|
|
|
It is legal though generally not very useful to reload built-in or dynamically
|
|
loaded modules, except for :mod:`sys`, :mod:`__main__` and :mod:`builtins`.
|
|
In many cases, however, extension modules are not designed to be initialized
|
|
more than once, and may fail in arbitrary ways when reloaded.
|
|
|
|
If a module imports objects from another module using :keyword:`from` ...
|
|
:keyword:`import` ..., calling :func:`reload` for the other module does not
|
|
redefine the objects imported from it --- one way around this is to re-execute
|
|
the :keyword:`!from` statement, another is to use :keyword:`!import` and qualified
|
|
names (*module*.*name*) instead.
|
|
|
|
If a module instantiates instances of a class, reloading the module that defines
|
|
the class does not affect the method definitions of the instances --- they
|
|
continue to use the old class definition. The same is true for derived classes.
|
|
|
|
.. versionchanged:: 3.3
|
|
Relies on both ``__name__`` and ``__loader__`` being defined on the module
|
|
being reloaded instead of just ``__name__``.
|
|
|
|
.. deprecated:: 3.4
|
|
Use :func:`importlib.reload` instead.
|
|
|
|
|
|
The following functions are conveniences for handling :pep:`3147` byte-compiled
|
|
file paths.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
.. function:: cache_from_source(path, debug_override=None)
|
|
|
|
Return the :pep:`3147` path to the byte-compiled file associated with the
|
|
source *path*. For example, if *path* is ``/foo/bar/baz.py`` the return
|
|
value would be ``/foo/bar/__pycache__/baz.cpython-32.pyc`` for Python 3.2.
|
|
The ``cpython-32`` string comes from the current magic tag (see
|
|
:func:`get_tag`; if :attr:`sys.implementation.cache_tag` is not defined then
|
|
:exc:`NotImplementedError` will be raised). By passing in ``True`` or
|
|
``False`` for *debug_override* you can override the system's value for
|
|
``__debug__``, leading to optimized bytecode.
|
|
|
|
*path* need not exist.
|
|
|
|
.. versionchanged:: 3.3
|
|
If :attr:`sys.implementation.cache_tag` is ``None``, then
|
|
:exc:`NotImplementedError` is raised.
|
|
|
|
.. deprecated:: 3.4
|
|
Use :func:`importlib.util.cache_from_source` instead.
|
|
|
|
.. versionchanged:: 3.5
|
|
The *debug_override* parameter no longer creates a ``.pyo`` file.
|
|
|
|
|
|
.. function:: source_from_cache(path)
|
|
|
|
Given the *path* to a :pep:`3147` file name, return the associated source code
|
|
file path. For example, if *path* is
|
|
``/foo/bar/__pycache__/baz.cpython-32.pyc`` the returned path would be
|
|
``/foo/bar/baz.py``. *path* need not exist, however if it does not conform
|
|
to :pep:`3147` format, a :exc:`ValueError` is raised. If
|
|
:attr:`sys.implementation.cache_tag` is not defined,
|
|
:exc:`NotImplementedError` is raised.
|
|
|
|
.. versionchanged:: 3.3
|
|
Raise :exc:`NotImplementedError` when
|
|
:attr:`sys.implementation.cache_tag` is not defined.
|
|
|
|
.. deprecated:: 3.4
|
|
Use :func:`importlib.util.source_from_cache` instead.
|
|
|
|
|
|
.. function:: get_tag()
|
|
|
|
Return the :pep:`3147` magic tag string matching this version of Python's
|
|
magic number, as returned by :func:`get_magic`.
|
|
|
|
.. deprecated:: 3.4
|
|
Use :attr:`sys.implementation.cache_tag` directly starting
|
|
in Python 3.3.
|
|
|
|
|
|
The following functions help interact with the import system's internal
|
|
locking mechanism. Locking semantics of imports are an implementation
|
|
detail which may vary from release to release. However, Python ensures
|
|
that circular imports work without any deadlocks.
|
|
|
|
|
|
.. function:: lock_held()
|
|
|
|
Return ``True`` if the global import lock is currently held, else
|
|
``False``. On platforms without threads, always return ``False``.
|
|
|
|
On platforms with threads, a thread executing an import first holds a
|
|
global import lock, then sets up a per-module lock for the rest of the
|
|
import. This blocks other threads from importing the same module until
|
|
the original import completes, preventing other threads from seeing
|
|
incomplete module objects constructed by the original thread. An
|
|
exception is made for circular imports, which by construction have to
|
|
expose an incomplete module object at some point.
|
|
|
|
.. versionchanged:: 3.3
|
|
The locking scheme has changed to per-module locks for
|
|
the most part. A global import lock is kept for some critical tasks,
|
|
such as initializing the per-module locks.
|
|
|
|
.. deprecated:: 3.4
|
|
|
|
|
|
.. function:: acquire_lock()
|
|
|
|
Acquire the interpreter's global import lock for the current thread.
|
|
This lock should be used by import hooks to ensure thread-safety when
|
|
importing modules.
|
|
|
|
Once a thread has acquired the import lock, the same thread may acquire it
|
|
again without blocking; the thread must release it once for each time it has
|
|
acquired it.
|
|
|
|
On platforms without threads, this function does nothing.
|
|
|
|
.. versionchanged:: 3.3
|
|
The locking scheme has changed to per-module locks for
|
|
the most part. A global import lock is kept for some critical tasks,
|
|
such as initializing the per-module locks.
|
|
|
|
.. deprecated:: 3.4
|
|
|
|
|
|
.. function:: release_lock()
|
|
|
|
Release the interpreter's global import lock. On platforms without
|
|
threads, this function does nothing.
|
|
|
|
.. versionchanged:: 3.3
|
|
The locking scheme has changed to per-module locks for
|
|
the most part. A global import lock is kept for some critical tasks,
|
|
such as initializing the per-module locks.
|
|
|
|
.. deprecated:: 3.4
|
|
|
|
|
|
The following constants with integer values, defined in this module, are used
|
|
to indicate the search result of :func:`find_module`.
|
|
|
|
|
|
.. data:: PY_SOURCE
|
|
|
|
The module was found as a source file.
|
|
|
|
.. deprecated:: 3.3
|
|
|
|
|
|
.. data:: PY_COMPILED
|
|
|
|
The module was found as a compiled code object file.
|
|
|
|
.. deprecated:: 3.3
|
|
|
|
|
|
.. data:: C_EXTENSION
|
|
|
|
The module was found as dynamically loadable shared library.
|
|
|
|
.. deprecated:: 3.3
|
|
|
|
|
|
.. data:: PKG_DIRECTORY
|
|
|
|
The module was found as a package directory.
|
|
|
|
.. deprecated:: 3.3
|
|
|
|
|
|
.. data:: C_BUILTIN
|
|
|
|
The module was found as a built-in module.
|
|
|
|
.. deprecated:: 3.3
|
|
|
|
|
|
.. data:: PY_FROZEN
|
|
|
|
The module was found as a frozen module.
|
|
|
|
.. deprecated:: 3.3
|
|
|
|
|
|
.. class:: NullImporter(path_string)
|
|
|
|
The :class:`NullImporter` type is a :pep:`302` import hook that handles
|
|
non-directory path strings by failing to find any modules. Calling this type
|
|
with an existing directory or empty string raises :exc:`ImportError`.
|
|
Otherwise, a :class:`NullImporter` instance is returned.
|
|
|
|
Instances have only one method:
|
|
|
|
.. method:: NullImporter.find_module(fullname [, path])
|
|
|
|
This method always returns ``None``, indicating that the requested module could
|
|
not be found.
|
|
|
|
.. versionchanged:: 3.3
|
|
``None`` is inserted into ``sys.path_importer_cache`` instead of an
|
|
instance of :class:`NullImporter`.
|
|
|
|
.. deprecated:: 3.4
|
|
Insert ``None`` into ``sys.path_importer_cache`` instead.
|
|
|
|
|
|
.. _examples-imp:
|
|
|
|
Examples
|
|
--------
|
|
|
|
The following function emulates what was the standard import statement up to
|
|
Python 1.4 (no hierarchical module names). (This *implementation* wouldn't work
|
|
in that version, since :func:`find_module` has been extended and
|
|
:func:`load_module` has been added in 1.4.) ::
|
|
|
|
import imp
|
|
import sys
|
|
|
|
def __import__(name, globals=None, locals=None, fromlist=None):
|
|
# Fast path: see if the module has already been imported.
|
|
try:
|
|
return sys.modules[name]
|
|
except KeyError:
|
|
pass
|
|
|
|
# If any of the following calls raises an exception,
|
|
# there's a problem we can't handle -- let the caller handle it.
|
|
|
|
fp, pathname, description = imp.find_module(name)
|
|
|
|
try:
|
|
return imp.load_module(name, fp, pathname, description)
|
|
finally:
|
|
# Since we may exit via an exception, close fp explicitly.
|
|
if fp:
|
|
fp.close()
|