cpython/Doc/library/imputil.rst

:mod:`imputil` --- Import utilities
===================================

.. module:: imputil
   :synopsis: Manage and augment the import process.


.. index:: statement: import

This module provides a very handy and useful mechanism for custom
:keyword:`import` hooks. Compared to the older :mod:`ihooks` module,
:mod:`imputil` takes a dramatically simpler and more straight-forward
approach to custom :keyword:`import` functions.


.. class:: ImportManager([fs_imp])

   Manage the import process.

   .. method:: ImportManager.install([namespace])

      Install this ImportManager into the specified namespace.

   .. method:: ImportManager.uninstall()

      Restore the previous import mechanism.

   .. method:: ImportManager.add_suffix(suffix, importFunc)

      Undocumented.


.. class:: Importer()

   Base class for replacing standard import functions.

   .. method:: Importer.import_top(name)

      Import a top-level module.

   .. method:: Importer.get_code(parent, modname, fqname)

      Find and retrieve the code for the given module.

      *parent* specifies a parent module to define a context for importing.
      It may be ``None``, indicating no particular context for the search.

      *modname* specifies a single module (not dotted) within the parent.

      *fqname* specifies the fully-qualified module name. This is a
      (potentially) dotted name from the "root" of the module namespace
      down to the modname.

      If there is no parent, then modname==fqname.

      This method should return ``None``, or a 3-tuple.

        * If the module was not found, then ``None`` should be returned.

        * The first item of the 2- or 3-tuple should be the integer 0 or 1,
          specifying whether the module that was found is a package or not.

        * The second item is the code object for the module (it will be
          executed within the new module's namespace). This item can also
          be a fully-loaded module object (e.g. loaded from a shared lib).

        * The third item is a dictionary of name/value pairs that will be
          inserted into new module before the code object is executed. This
          is provided in case the module's code expects certain values (such
          as where the module was found). When the second item is a module
          object, then these names/values will be inserted *after* the module
          has been loaded/initialized.


.. class:: BuiltinImporter()

   Emulate the import mechanism for builtin and frozen modules.  This is a
   sub-class of the :class:`Importer` class.

   .. method:: BuiltinImporter.get_code(parent, modname, fqname)

      Undocumented.

.. function:: py_suffix_importer(filename, finfo, fqname)

   Undocumented.

.. class:: DynLoadSuffixImporter([desc])

   Undocumented.

   .. method:: DynLoadSuffixImporter.import_file(filename, finfo, fqname)

      Undocumented.

.. _examples-imputil:

Examples
--------

This is a re-implementation of hierarchical module import.

This code is intended to be read, not executed.  However, it does work
-- all you need to do to enable it is "import knee".

(The name is a pun on the klunkier predecessor of this module, "ni".)

::

   import sys, imp, builtins

   # Replacement for __import__()
   def import_hook(name, globals=None, locals=None, fromlist=None):
       parent = determine_parent(globals)
       q, tail = find_head_package(parent, name)
       m = load_tail(q, tail)
       if not fromlist:
           return q
       if hasattr(m, "__path__"):
           ensure_fromlist(m, fromlist)
       return m

   def determine_parent(globals):
       if not globals or  not "__name__" in globals:
           return None
       pname = globals['__name__']
       if "__path__" in globals:
           parent = sys.modules[pname]
           assert globals is parent.__dict__
           return parent
       if '.' in pname:
           i = pname.rfind('.')
           pname = pname[:i]
           parent = sys.modules[pname]
           assert parent.__name__ == pname
           return parent
       return None

   def find_head_package(parent, name):
       if '.' in name:
           i = name.find('.')
           head = name[:i]
           tail = name[i+1:]
       else:
           head = name
           tail = ""
       if parent:
           qname = "%s.%s" % (parent.__name__, head)
       else:
           qname = head
       q = import_module(head, qname, parent)
       if q: return q, tail
       if parent:
           qname = head
           parent = None
           q = import_module(head, qname, parent)
           if q: return q, tail
       raise ImportError("No module named " + qname)

   def load_tail(q, tail):
       m = q
       while tail:
           i = tail.find('.')
           if i < 0: i = len(tail)
           head, tail = tail[:i], tail[i+1:]
           mname = "%s.%s" % (m.__name__, head)
           m = import_module(head, mname, m)
           if not m:
               raise ImportError("No module named " + mname)
       return m

   def ensure_fromlist(m, fromlist, recursive=0):
       for sub in fromlist:
           if sub == "*":
               if not recursive:
                   try:
                       all = m.__all__
                   except AttributeError:
                       pass
                   else:
                       ensure_fromlist(m, all, 1)
               continue
           if sub != "*" and not hasattr(m, sub):
               subname = "%s.%s" % (m.__name__, sub)
               submod = import_module(sub, subname, m)
               if not submod:
                   raise ImportError("No module named " + subname)

   def import_module(partname, fqname, parent):
       try:
           return sys.modules[fqname]
       except KeyError:
           pass
       try:
           fp, pathname, stuff = imp.find_module(partname,
                                                 parent and parent.__path__)
       except ImportError:
           return None
       try:
           m = imp.load_module(fqname, fp, pathname, stuff)
       finally:
           if fp: fp.close()
       if parent:
           setattr(parent, partname, m)
       return m


   # Replacement for reload()
   def reload_hook(module):
       name = module.__name__
       if '.' not in name:
           return import_module(name, name, None)
       i = name.rfind('.')
       pname = name[:i]
       parent = sys.modules[pname]
       return import_module(name[i+1:], name, parent)


   # Save the original hooks
   original_import = builtins.__import__
   original_reload = builtins.reload

   # Now install our hooks
   builtins.__import__ = import_hook
   builtins.reload = reload_hook

.. index::
   module: knee

Also see the :mod:`importers` module (which can be found
in :file:`Demo/imputil/` in the Python source distribution) for additional
examples.