cpython/Doc/library/winreg.rst

:mod:`winreg` -- Windows registry access
=========================================

.. module:: winreg
   :platform: Windows
   :synopsis: Routines and objects for manipulating the Windows registry.
.. sectionauthor:: Mark Hammond <MarkH@ActiveState.com>


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:


.. function:: 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
   :meth:`handle.Close`), it is closed when the *hkey* object is destroyed by
   Python.


.. function:: ConnectRegistry(computer_name, key)

   Establishes a connection to a predefined registry handle on another computer,
   and returns a :ref:`handle object <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
   :exc:`WindowsError` exception is raised.


.. function:: CreateKey(key, sub_key)

   Creates or opens the specified key, returning a
   :ref:`handle object <handle-object>`.

   *key* is an already open key, or one of the predefined :const:`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
   :exc:`WindowsError` exception is raised.


.. function:: DeleteKey(key, sub_key)

   Deletes the specified key.

   *key* is an already open key, or any one of the predefined  :const:`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 :exc:`WindowsError` exception is raised.


.. function:: DeleteValue(key, value)

   Removes a named value from a registry key.

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

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


.. function:: 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 :const:`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 :exc:`WindowsError` exception is
   raised, indicating, no more values are available.


.. function:: 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 :const:`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 :exc:`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                                 |
   +-------+--------------------------------------------+


.. function:: ExpandEnvironmentStrings(str)

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

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


.. function:: FlushKey(key)

   Writes all the attributes of a key to the registry.

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

   It is not necessary to call :func:`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 :func:`CloseKey`, the
   :func:`FlushKey` method returns only when all the data has been written to the
   registry. An application should only call :func:`FlushKey` if it requires
   absolute certainty that registry changes are on disk.

   .. note::

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


.. function:: 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 :const:`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 :func:`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
   :const:`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 :func:`ConnectRegistry`, then the path
   specified in *fileName* is relative to the remote computer.

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


.. function:: OpenKey(key, sub_key[, res[, sam]])

   Opens the specified key, returning a :ref:`handle object <handle-object>`.

   *key* is an already open key, or any one of the predefined :const:`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 :const:`KEY_READ`.

   The result is a new handle to the specified key.

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


.. function:: OpenKeyEx()

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


.. function:: QueryInfoKey(key)

   Returns information about a key, as a tuple.

   *key* is an already open key, or one of the predefined :const:`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.              |
   +-------+---------------------------------------------+


.. function:: 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 :const:`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 :func:`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
   :func:`QueryValueEx` if possible.


.. function:: 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 :const:`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.                             |
   +-------+-----------------------------------------+


.. function:: 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 :const:`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 :meth:`LoadKey`, :meth:`ReplaceKey`
   or :meth:`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 :const:`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.


.. function:: SetValue(key, sub_key, type, value)

   Associates a value with a specified key.

   *key* is an already open key, or one of the predefined :const:`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
   :const:`REG_SZ`, meaning only strings are supported.  Use the :func:`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
   :const:`KEY_SET_VALUE` access.


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

   To open the key, use the :func:`CreateKey` or :func:`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.


.. _handle-object:

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
:meth:`Close` method on the object, or the :func:`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 :meth:`__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
:func:`int` function), in which case the underlying Windows handle value is
returned.  You can also use the :meth:`Detach` method to return the integer
handle, and also disconnect the Windows handle from the handle object.


.. method:: PyHKEY.Close()

   Closes the underlying Windows handle.

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


.. method:: 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.

.. method:: PyHKEY.__enter__()
            PyHKEY.__exit__(\*exc_info)

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

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

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