34.3. "winreg" — Windows registry access
****************************************

======================================================================

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.

Changed in version 3.3: Several functions in this module used to raise
a "WindowsError", which is now an alias of "OSError".


34.3.1. Functions
=================

This module offers the following functions:

winreg.CloseKey(hkey)

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

   Note: If *hkey* is not closed using this method (or via
     "hkey.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, an "OSError" exception is raised.

   Changed in version 3.3: See above.

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, an "OSError" exception is raised.

   Changed in version 3.3: See above.

winreg.CreateKeyEx(key, sub_key, reserved=0, access=KEY_WRITE)

   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.

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

   *access* is an integer that specifies an access mask that describes
   the desired security access for the key.  Default is "KEY_WRITE".
   See Access Rights for other allowed values.

   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, an "OSError" exception is raised.

   New in version 3.2.

   Changed in version 3.3: See above.

winreg.DeleteKey(key, sub_key)

   Deletes the specified key.

   *key* is an already open key, or 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, an "OSError" exception is
   raised.

   Changed in version 3.3: See above.

winreg.DeleteKeyEx(key, sub_key, access=KEY_WOW64_64KEY, reserved=0)

   Deletes the specified key.

   Note: The "DeleteKeyEx()" function is implemented with the
     RegDeleteKeyEx Windows API function, which is specific to 64-bit
     versions of Windows. See the RegDeleteKeyEx documentation.

   *key* is an already open key, or 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.

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

   *access* is an integer that specifies an access mask that describes
   the desired security access for the key.  Default is
   "KEY_WOW64_64KEY".  See Access Rights for other allowed values.

   *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, an "OSError" exception is
   raised.

   On unsupported Windows versions, "NotImplementedError" is raised.

   New in version 3.2.

   Changed in version 3.3: See above.

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 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 an "OSError"
   exception is raised, indicating, no more values are available.

   Changed in version 3.3: See above.

winreg.EnumValue(key, index)

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

   *key* is an already open key, or 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 an "OSError"
   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 (see table in docs for            |
   |         | "SetValueEx()")                              |
   +---------+----------------------------------------------+

   Changed in version 3.3: See above.

winreg.ExpandEnvironmentStrings(str)

   Expands environment variable placeholders "%NAME%" in strings 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 a handle returned by "ConnectRegistry()" or one of the
   constants "HKEY_USERS" or "HKEY_LOCAL_MACHINE".

   *sub_key* is a string that identifies the subkey 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 from permissions – see the RegLoadKey documentation for
   more details.

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

winreg.OpenKey(key, sub_key, reserved=0, access=KEY_READ)
winreg.OpenKeyEx(key, sub_key, reserved=0, access=KEY_READ)

   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 identifies the sub_key to open.

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

   *access* is an integer that specifies an access mask that describes
   the desired security access for the key.  Default is "KEY_READ".
   See Access Rights for other allowed values.

   The result is a new handle to the specified key.

   If the function fails, "OSError" is raised.

   Changed in version 3.2: Allow the use of named arguments.

   Changed in version 3.3: See above.

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, 1601.                |
   +---------+-----------------------------------------------+

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 (see table in docs for         |
   |         | "SetValueEx()")                           |
   +---------+-------------------------------------------+

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()" method.

   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 Conflicts Between User Rights and Permissions 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.

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

   *type* is an integer that specifies the type of the data. See Value
   Types for the available types.

   *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.

winreg.DisableReflectionKey(key)

   Disables registry reflection for 32-bit processes running on a
   64-bit operating system.

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

   Will generally raise "NotImplemented" if executed on a 32-bit
   operating system.

   If the key is not on the reflection list, the function succeeds but
   has no effect.  Disabling reflection for a key does not affect
   reflection of any subkeys.

winreg.EnableReflectionKey(key)

   Restores registry reflection for the specified disabled key.

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

   Will generally raise "NotImplemented" if executed on a 32-bit
   operating system.

   Restoring reflection for a key does not affect reflection of any
   subkeys.

winreg.QueryReflectionKey(key)

   Determines the reflection state for the specified key.

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

   Returns "True" if reflection is disabled.

   Will generally raise "NotImplemented" if executed on a 32-bit
   operating system.


34.3.2. Constants
=================

The following constants are defined for use in many "_winreg"
functions.


34.3.2.1. HKEY_* Constants
--------------------------

winreg.HKEY_CLASSES_ROOT

   Registry entries subordinate to this key define types (or classes)
   of documents and the properties associated with those types. Shell
   and COM applications use the information stored under this key.

winreg.HKEY_CURRENT_USER

   Registry entries subordinate to this key define the preferences of
   the current user. These preferences include the settings of
   environment variables, data about program groups, colors, printers,
   network connections, and application preferences.

winreg.HKEY_LOCAL_MACHINE

   Registry entries subordinate to this key define the physical state
   of the computer, including data about the bus type, system memory,
   and installed hardware and software.

winreg.HKEY_USERS

   Registry entries subordinate to this key define the default user
   configuration for new users on the local computer and the user
   configuration for the current user.

winreg.HKEY_PERFORMANCE_DATA

   Registry entries subordinate to this key allow you to access
   performance data. The data is not actually stored in the registry;
   the registry functions cause the system to collect the data from
   its source.

winreg.HKEY_CURRENT_CONFIG

   Contains information about the current hardware profile of the
   local computer system.

winreg.HKEY_DYN_DATA

   This key is not used in versions of Windows after 98.


34.3.2.2. Access Rights
-----------------------

For more information, see Registry Key Security and Access.

winreg.KEY_ALL_ACCESS

   Combines the STANDARD_RIGHTS_REQUIRED, "KEY_QUERY_VALUE",
   "KEY_SET_VALUE", "KEY_CREATE_SUB_KEY", "KEY_ENUMERATE_SUB_KEYS",
   "KEY_NOTIFY", and "KEY_CREATE_LINK" access rights.

winreg.KEY_WRITE

   Combines the STANDARD_RIGHTS_WRITE, "KEY_SET_VALUE", and
   "KEY_CREATE_SUB_KEY" access rights.

winreg.KEY_READ

   Combines the STANDARD_RIGHTS_READ, "KEY_QUERY_VALUE",
   "KEY_ENUMERATE_SUB_KEYS", and "KEY_NOTIFY" values.

winreg.KEY_EXECUTE

   Equivalent to "KEY_READ".

winreg.KEY_QUERY_VALUE

   Required to query the values of a registry key.

winreg.KEY_SET_VALUE

   Required to create, delete, or set a registry value.

winreg.KEY_CREATE_SUB_KEY

   Required to create a subkey of a registry key.

winreg.KEY_ENUMERATE_SUB_KEYS

   Required to enumerate the subkeys of a registry key.

winreg.KEY_NOTIFY

   Required to request change notifications for a registry key or for
   subkeys of a registry key.

winreg.KEY_CREATE_LINK

   Reserved for system use.


34.3.2.2.1. 64-bit Specific
~~~~~~~~~~~~~~~~~~~~~~~~~~~

For more information, see Accessing an Alternate Registry View.

winreg.KEY_WOW64_64KEY

   Indicates that an application on 64-bit Windows should operate on
   the 64-bit registry view.

winreg.KEY_WOW64_32KEY

   Indicates that an application on 64-bit Windows should operate on
   the 32-bit registry view.


34.3.2.3. Value Types
---------------------

For more information, see Registry Value Types.

winreg.REG_BINARY

   Binary data in any form.

winreg.REG_DWORD

   32-bit number.

winreg.REG_DWORD_LITTLE_ENDIAN

   A 32-bit number in little-endian format. Equivalent to "REG_DWORD".

winreg.REG_DWORD_BIG_ENDIAN

   A 32-bit number in big-endian format.

winreg.REG_EXPAND_SZ

   Null-terminated string containing references to environment
   variables ("%PATH%").

winreg.REG_LINK

   A Unicode symbolic link.

winreg.REG_MULTI_SZ

   A sequence of null-terminated strings, terminated by two null
   characters. (Python handles this termination automatically.)

winreg.REG_NONE

   No defined value type.

winreg.REG_QWORD

   A 64-bit number.

   New in version 3.6.

winreg.REG_QWORD_LITTLE_ENDIAN

   A 64-bit number in little-endian format. Equivalent to "REG_QWORD".

   New in version 3.6.

winreg.REG_RESOURCE_LIST

   A device-driver resource list.

winreg.REG_FULL_RESOURCE_DESCRIPTOR

   A hardware setting.

winreg.REG_RESOURCE_REQUIREMENTS_LIST

   A hardware resource list.

winreg.REG_SZ

   A null-terminated string.


34.3.3. 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.
