
``winreg`` -- Windows registry access
*************************************

Platform: Windows

*Platforms: *Windows

These functions expose the Windows registry API to Python.  Instead of
using an integer as the registry handle, a handle object is used to
ensure that the handles are closed correctly, even if the programmer
neglects to explicitly close them.

This module exposes a very low-level interface to the Windows
registry; it is expected that in the future a new ``winreg``  module
will be created offering a higher-level interface to the registry API.

This module offers the following functions:

winreg.CloseKey(hkey)

   Closes a previously opened registry key. The hkey argument
   specifies a previously opened key.

   Note that if *hkey* is not closed using this method (or via
   ``handle.Close()``), it is closed when the *hkey* object is
   destroyed by Python.

winreg.ConnectRegistry(computer_name, key)

   Establishes a connection to a predefined registry handle on
   another computer, and returns a *handle object*

   *computer_name* is the name of the remote computer, of the  form
   ``r"\\computername"``.  If ``None``, the local computer is used.

   *key* is the predefined handle to connect to.

   The return value is the handle of the opened key. If the function
   fails, a ``WindowsError`` exception is  raised.

winreg.CreateKey(key, sub_key)

   Creates or opens the specified key, returning a *handle object*

   *key* is an already open key, or one of the predefined  ``HKEY_*``
   constants.

   *sub_key* is a string that names the key this method opens  or
   creates.

   If *key* is one of the predefined keys, *sub_key* may  be ``None``.
   In that case, the handle returned is the same key handle  passed in
   to the function.

   If the key already exists, this function opens the existing key.

   The return value is the handle of the opened key. If the function
   fails, a ``WindowsError`` exception is  raised.

winreg.DeleteKey(key, sub_key)

   Deletes the specified key.

   *key* is an already open key, or any one of the predefined
   ``HKEY_*`` constants.

   *sub_key* is a string that must be a subkey of the key  identified
   by the *key* parameter.  This value must not be  ``None``, and the
   key may not have subkeys.

   *This method can not delete keys with subkeys.*

   If the method succeeds, the entire key, including all of its
   values, is removed. If the method fails, a ``WindowsError``
   exception is raised.

winreg.DeleteValue(key, value)

   Removes a named value from a registry key.

   *key* is an already open key, or one of the predefined  ``HKEY_*``
   constants.

   *value* is a string that identifies the value to remove.

winreg.EnumKey(key, index)

   Enumerates subkeys of an open registry key, returning a string.

   *key* is an already open key, or any one of the predefined
   ``HKEY_*`` constants.

   *index* is an integer that identifies the index of the key to
   retrieve.

   The function retrieves the name of one subkey each time it  is
   called.  It is typically called repeatedly until a
   ``WindowsError`` exception  is raised, indicating, no more values
   are available.

winreg.EnumValue(key, index)

   Enumerates values of an open registry key, returning a tuple.

   *key* is an already open key, or any one of the predefined
   ``HKEY_*`` constants.

   *index* is an integer that identifies the index of the value  to
   retrieve.

   The function retrieves the name of one subkey each time it is
   called. It is typically called repeatedly, until a
   ``WindowsError`` exception is raised, indicating  no more values.

   The result is a tuple of 3 items:

   +---------+----------------------------------------------+
   | Index   | Meaning                                      |
   +=========+==============================================+
   | ``0``   | A string that identifies the value name      |
   +---------+----------------------------------------------+
   | ``1``   | An object that holds the value data, and     |
   |         | whose type depends on the underlying         |
   |         | registry type                                |
   +---------+----------------------------------------------+
   | ``2``   | An integer that identifies the type of the   |
   |         | value data                                   |
   +---------+----------------------------------------------+

winreg.ExpandEnvironmentStrings(str)

   Expands environment strings %NAME% in unicode string like
   ``REG_EXPAND_SZ``:

      >>> ExpandEnvironmentStrings('%windir%')
      'C:\\Windows'

winreg.FlushKey(key)

   Writes all the attributes of a key to the registry.

   *key* is an already open key, or one of the predefined  ``HKEY_*``
   constants.

   It is not necessary to call ``FlushKey()`` to change a key.
   Registry changes are flushed to disk by the registry using its lazy
   flusher.  Registry changes are also flushed to disk at system
   shutdown.  Unlike ``CloseKey()``, the ``FlushKey()`` method
   returns only when all the data has been written to the registry. An
   application should only call ``FlushKey()`` if it requires absolute
   certainty that registry changes are on disk.

   Note: If you don't know whether a ``FlushKey()`` call is required, it
     probably isn't.

winreg.LoadKey(key, sub_key, file_name)

   Creates a subkey under the specified key and stores registration
   information from a specified file into that subkey.

   *key* is an already open key, or any of the predefined ``HKEY_*``
   constants.

   *sub_key* is a string that identifies the sub_key to load.

   *file_name* is the name of the file to load registry data from.
   This file must have been created with the ``SaveKey()`` function.
   Under the file allocation table (FAT) file system, the filename may
   not have an extension.

   A call to LoadKey() fails if the calling process does not have the
   ``SE_RESTORE_PRIVILEGE`` privilege. Note that privileges are
   different than permissions - see the Win32 documentation for more
   details.

   If *key* is a handle returned by ``ConnectRegistry()``,  then the
   path specified in *fileName* is relative to the  remote computer.

   The Win32 documentation implies *key* must be in the  ``HKEY_USER``
   or ``HKEY_LOCAL_MACHINE`` tree. This may or may not be true.

winreg.OpenKey(key, sub_key, res=0, sam=KEY_READ)

   Opens the specified key, returning a *handle object*

   *key* is an already open key, or any one of the predefined
   ``HKEY_*`` constants.

   *sub_key* is a string that identifies the sub_key to open.

   *res* is a reserved integer, and must be zero.  The default is
   zero.

   *sam* is an integer that specifies an access mask that describes
   the desired security access for the key.  Default is ``KEY_READ``.

   The result is a new handle to the specified key.

   If the function fails, ``WindowsError`` is raised.

winreg.OpenKeyEx()

   The functionality of ``OpenKeyEx()`` is provided via ``OpenKey()``,
   by the use of default arguments.

winreg.QueryInfoKey(key)

   Returns information about a key, as a tuple.

   *key* is an already open key, or one of the predefined  ``HKEY_*``
   constants.

   The result is a tuple of 3 items:

   +---------+-----------------------------------------------+
   | Index   | Meaning                                       |
   +=========+===============================================+
   | ``0``   | An integer giving the number of sub keys this |
   |         | key has.                                      |
   +---------+-----------------------------------------------+
   | ``1``   | An integer giving the number of values this   |
   |         | key has.                                      |
   +---------+-----------------------------------------------+
   | ``2``   | An integer giving when the key was last       |
   |         | modified (if available) as 100's of           |
   |         | nanoseconds since Jan 1, 1600.                |
   +---------+-----------------------------------------------+

winreg.QueryValue(key, sub_key)

   Retrieves the unnamed value for a key, as a string

   *key* is an already open key, or one of the predefined  ``HKEY_*``
   constants.

   *sub_key* is a string that holds the name of the subkey with which
   the value is associated.  If this parameter is ``None`` or empty,
   the  function retrieves the value set by the ``SetValue()`` method
   for the key identified by *key*.

   Values in the registry have name, type, and data components. This
   method retrieves the data for a key's first value that has a NULL
   name. But the underlying API call doesn't return the type, so
   always use ``QueryValueEx()`` if possible.

winreg.QueryValueEx(key, value_name)

   Retrieves the type and data for a specified value name associated
   with  an open registry key.

   *key* is an already open key, or one of the predefined  ``HKEY_*``
   constants.

   *value_name* is a string indicating the value to query.

   The result is a tuple of 2 items:

   +---------+-------------------------------------------+
   | Index   | Meaning                                   |
   +=========+===========================================+
   | ``0``   | The value of the registry item.           |
   +---------+-------------------------------------------+
   | ``1``   | An integer giving the registry type for   |
   |         | this value.                               |
   +---------+-------------------------------------------+

winreg.SaveKey(key, file_name)

   Saves the specified key, and all its subkeys to the specified file.

   *key* is an already open key, or one of the predefined  ``HKEY_*``
   constants.

   *file_name* is the name of the file to save registry data to. This
   file cannot already exist. If this filename includes an extension,
   it cannot be used on file allocation table (FAT) file systems by
   the ``LoadKey()``, ``ReplaceKey()`` or  ``RestoreKey()`` methods.

   If *key* represents a key on a remote computer, the path  described
   by *file_name* is relative to the remote computer. The caller of
   this method must possess the ``SeBackupPrivilege``  security
   privilege.  Note that privileges are different than permissions  -
   see the Win32 documentation for more details.

   This function passes NULL for *security_attributes* to the API.

winreg.SetValue(key, sub_key, type, value)

   Associates a value with a specified key.

   *key* is an already open key, or one of the predefined  ``HKEY_*``
   constants.

   *sub_key* is a string that names the subkey with which the value
   is associated.

   *type* is an integer that specifies the type of the data. Currently
   this must be ``REG_SZ``, meaning only strings are supported.  Use
   the ``SetValueEx()`` function for support for other data types.

   *value* is a string that specifies the new value.

   If the key specified by the *sub_key* parameter does not exist, the
   SetValue function creates it.

   Value lengths are limited by available memory. Long values (more
   than 2048 bytes) should be stored as files with the filenames
   stored in the configuration registry.  This helps the registry
   perform efficiently.

   The key identified by the *key* parameter must have been  opened
   with ``KEY_SET_VALUE`` access.

winreg.SetValueEx(key, value_name, reserved, type, value)

   Stores data in the value field of an open registry key.

   *key* is an already open key, or one of the predefined  ``HKEY_*``
   constants.

   *value_name* is a string that names the subkey with which the
   value is associated.

   *type* is an integer that specifies the type of the data.   This
   should be one of the following constants defined in this module:

   +------------------------------------+-----------------------------------------------+
   | Constant                           | Meaning                                       |
   +====================================+===============================================+
   | ``REG_BINARY``                     | Binary data in any form.                      |
   +------------------------------------+-----------------------------------------------+
   | ``REG_DWORD``                      | A 32-bit number.                              |
   +------------------------------------+-----------------------------------------------+
   | ``REG_DWORD_LITTLE_ENDIAN``        | A 32-bit number in little-endian format.      |
   +------------------------------------+-----------------------------------------------+
   | ``REG_DWORD_BIG_ENDIAN``           | A 32-bit number in big-endian format.         |
   +------------------------------------+-----------------------------------------------+
   | ``REG_EXPAND_SZ``                  | Null-terminated string containing references  |
   |                                    | to environment variables (``%PATH%``).        |
   +------------------------------------+-----------------------------------------------+
   | ``REG_LINK``                       | A Unicode symbolic link.                      |
   +------------------------------------+-----------------------------------------------+
   | ``REG_MULTI_SZ``                   | A sequence of null-terminated strings,        |
   |                                    | terminated by two null characters.  (Python   |
   |                                    | handles  this termination automatically.)     |
   +------------------------------------+-----------------------------------------------+
   | ``REG_NONE``                       | No defined value type.                        |
   +------------------------------------+-----------------------------------------------+
   | ``REG_RESOURCE_LIST``              | A device-driver resource list.                |
   +------------------------------------+-----------------------------------------------+
   | ``REG_SZ``                         | A null-terminated string.                     |
   +------------------------------------+-----------------------------------------------+

   *reserved* can be anything - zero is always passed to the  API.

   *value* is a string that specifies the new value.

   This method can also set additional value and type information for
   the specified key.  The key identified by the key parameter must
   have been opened with ``KEY_SET_VALUE`` access.

   To open the key, use the ``CreateKey()`` or  ``OpenKey()`` methods.

   Value lengths are limited by available memory. Long values (more
   than 2048 bytes) should be stored as files with the filenames
   stored in the configuration registry.  This helps the registry
   perform efficiently.


Registry Handle Objects
=======================

This object wraps a Windows HKEY object, automatically closing it when
the object is destroyed.  To guarantee cleanup, you can call either
the ``Close()`` method on the object, or the  ``CloseKey()`` function.

All registry functions in this module return one of these objects.

All registry functions in this module which accept a handle object
also accept an integer, however, use of the handle object is
encouraged.

Handle objects provide semantics for ``__bool__()`` - thus

   if handle:
       print("Yes")

will print ``Yes`` if the handle is currently valid (has not been
closed or detached).

The object also support comparison semantics, so handle objects will
compare true if they both reference the same underlying Windows handle
value.

Handle objects can be converted to an integer (e.g., using the built-
in ``int()`` function), in which case the underlying Windows handle
value is returned.  You can also use the  ``Detach()`` method to
return the integer handle, and also disconnect the Windows handle from
the handle object.

PyHKEY.Close()

   Closes the underlying Windows handle.

   If the handle is already closed, no error is raised.

PyHKEY.Detach()

   Detaches the Windows handle from the handle object.

   The result is an integer that holds the value of the handle before
   it is detached.  If the handle is already detached or closed, this
   will return zero.

   After calling this function, the handle is effectively invalidated,
   but the handle is not closed.  You would call this function when
   you need the underlying Win32 handle to exist beyond the lifetime
   of the handle object.

PyHKEY.__enter__()
PyHKEY.__exit__(*exc_info)

   The HKEY object implements ``__enter__()`` and ``__exit__()`` and
   thus supports the context protocol for the ``with`` statement:

      with OpenKey(HKEY_LOCAL_MACHINE, "foo") as key:
          # ... work with key ...

   will automatically close *key* when control leaves the ``with``
   block.
