imp — Access the import internals¶Source code: Lib/imp.py
This module provides an interface to the mechanisms used to implement the
import statement. It defines the following constants and functions:
imp.get_magic()¶Return the magic string value used to recognize byte-compiled code files
(.pyc files). (This value may be different for each Python version.)
Deprecated since version 3.4: Use importlib.util.MAGIC_NUMBER instead.
imp.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 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
PY_SOURCE, PY_COMPILED, or C_EXTENSION, described
below.
Deprecated since version 3.3: Use the constants defined on importlib.machinery instead.
imp.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 (C_BUILTIN), then a frozen module (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 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 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 get_suffixes() describing the kind of
module found.
If the module does not live in a file, the returned file is None,
pathname is the empty string, 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, 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 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
find_module() and load_module() to find and load package P, and
then use find_module() with the path argument set to P.__path__.
When P itself has a dotted name, apply this recipe recursively.
Deprecated since version 3.3: Use importlib.util.find_spec() instead unless Python 3.3
compatibility is required, in which case use
importlib.find_loader(). For example usage of the former case,
see the Examples section of the importlib
documentation.
imp.load_module(name, file, pathname, description)¶Load a module that was previously found by 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 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 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 try ... finally statement.
Deprecated since version 3.3: If previously used in conjunction with imp.find_module() then
consider using importlib.import_module(), otherwise use the loader
returned by the replacement you chose for imp.find_module(). If you
called imp.load_module() and related functions directly with file
path arguments then use a combination of
importlib.util.spec_from_file_location() and
importlib.util.module_from_spec(). See the Examples
section of the importlib documentation for details of the various
approaches.
imp.new_module(name)¶Return a new empty module object called name. This object is not inserted
in sys.modules.
Deprecated since version 3.4: Use importlib.util.module_from_spec() instead.
imp.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:
init function of extension modules is not called a second
time.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 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 sys, __main__ and 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 from ...
import ..., calling reload() for the other module does not
redefine the objects imported from it — one way around this is to re-execute
the from statement, another is to use 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.
Changed in version 3.3: Relies on both __name__ and __loader__ being defined on the module
being reloaded instead of just __name__.
Deprecated since version 3.4: Use importlib.reload() instead.
The following functions are conveniences for handling PEP 3147 byte-compiled file paths.
New in version 3.2.
imp.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
get_tag(); if sys.implementation.cache_tag is not defined then
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.
Changed in version 3.3: If sys.implementation.cache_tag is None, then
NotImplementedError is raised.
Deprecated since version 3.4: Use importlib.util.cache_from_source() instead.
Changed in version 3.5: The debug_override parameter no longer creates a .pyo file.
imp.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 ValueError is raised. If
sys.implementation.cache_tag is not defined,
NotImplementedError is raised.
Changed in version 3.3: Raise NotImplementedError when
sys.implementation.cache_tag is not defined.
Deprecated since version 3.4: Use importlib.util.source_from_cache() instead.
imp.get_tag()¶Return the PEP 3147 magic tag string matching this version of Python’s
magic number, as returned by get_magic().
Deprecated since version 3.4: Use 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.
imp.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.
Changed in version 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 since version 3.4.
imp.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.
Changed in version 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 since version 3.4.
imp.release_lock()¶Release the interpreter’s global import lock. On platforms without threads, this function does nothing.
Changed in version 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 since version 3.4.
The following constants with integer values, defined in this module, are used
to indicate the search result of find_module().
imp.PY_SOURCE¶The module was found as a source file.
Deprecated since version 3.3.
imp.PY_COMPILED¶The module was found as a compiled code object file.
Deprecated since version 3.3.
imp.C_EXTENSION¶The module was found as dynamically loadable shared library.
Deprecated since version 3.3.
imp.PKG_DIRECTORY¶The module was found as a package directory.
Deprecated since version 3.3.
imp.C_BUILTIN¶The module was found as a built-in module.
Deprecated since version 3.3.
imp.PY_FROZEN¶The module was found as a frozen module.
Deprecated since version 3.3.
imp.NullImporter(path_string)¶The 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 ImportError.
Otherwise, a NullImporter instance is returned.
Instances have only one method:
find_module(fullname[, path])¶This method always returns None, indicating that the requested module could
not be found.
Changed in version 3.3: None is inserted into sys.path_importer_cache instead of an
instance of NullImporter.
Deprecated since version 3.4: Insert None into sys.path_importer_cache instead.
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 find_module() has been extended and
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()