Issue #18193: Add importlib.reload(), documenting (but not

implementing in code) the deprecation of imp.reload().

Thanks to Berker Peksag for the patch.

2 files changed, 70 insertions, 0 deletions

diff --git a/Doc/library/imp.rst b/Doc/library/imp.rst
index e090e00..8a75d4c 100644
--- a/Doc/library/imp.rst
+++ b/Doc/library/imp.rst
@@ -171,6 +171,9 @@ This module provides an interface to the mechanisms used to implement the
    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.
 
+   .. deprecated:: 3.4
+      Use :func:`importlib.reload` instead.
+
 
 The following functions are conveniences for handling :pep:`3147` byte-compiled
 file paths.
diff --git a/Doc/library/importlib.rst b/Doc/library/importlib.rst
index d9e4273..0caabaa 100644
--- a/Doc/library/importlib.rst
+++ b/Doc/library/importlib.rst
@@ -115,6 +115,73 @@ Functions
 
    .. versionadded:: 3.3
 
+.. 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 :func:`.reload` is executed:
+
+   * Python modules' code is recompiled and the module-level code re-executed,
+     defining a new set of objects which are bound to names in the module's
+     dictionary by reusing the :term:`loader` which originally loaded the
+     module.  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:
+
+   If a module is syntactically correct but its initialization fails, the first
+   :keyword:`import` statement for it does not bind its name locally, but does
+   store a (partially initialized) module object in ``sys.modules``.  To reload
+   the module you must first :keyword:`import` it again (this will bind the name
+   to the partially initialized module object) before you can :func:`reload` it.
+
+   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 (this is not true for e.g. :mod:`sys`,
+   :mod:`__main__`, :mod:`__builtin__` and other key modules where reloading is
+   frowned upon). 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.
+
+   .. versionadded:: 3.4
+
 
 :mod:`importlib.abc` -- Abstract base classes related to import
 ---------------------------------------------------------------