dbm.gnu and dbm.ndbm accept both strings and bytes as keys and values. For the

former they are converted to bytes before being written to the DB.

Closes issue 3799. Reviewed by Skip Montanaro.

1 files changed, 24 insertions, 15 deletions

diff --git a/Doc/library/dbm.rst b/Doc/library/dbm.rst
index ed05921..84edbbe 100644
--- a/Doc/library/dbm.rst
+++ b/Doc/library/dbm.rst
@@ -52,7 +52,9 @@
 The object returned by :func:`open` supports most of the same functionality as
 dictionaries; keys and their corresponding values can be stored, retrieved, and
 deleted, and the :keyword:`in` operator and the :meth:`keys` method are
-available.  Keys and values must always be strings.
+available. Key and values are always stored as bytes. This means that when
+strings are used they are implicitly converted to the default encoding before
+being stored.
 
 The following example records some hostnames and a corresponding title,  and
 then prints out the contents of the database::
@@ -63,9 +65,15 @@ then prints out the contents of the database::
    db = dbm.open('cache', 'c')
 
    # Record some values
+   db[b'hello'] = b'there'
    db['www.python.org'] = 'Python Website'
    db['www.cnn.com'] = 'Cable News Network'
 
+   # Note that the keys are considered bytes now.
+   assert db[b'www.python.org'] == b'Python Website'
+   # Notice how the value is now in bytes.
+   assert db['www.cnn.com'] == b'Cable News Network'
+
    # Loop through contents.  Other dictionary methods
    # such as .keys(), .values() also work.
    for k, v in db.iteritems():
@@ -98,17 +106,18 @@ The individual submodules are described in the following sections.
 
 This module is quite similar to the :mod:`dbm` module, but uses the GNU library
 ``gdbm`` instead to provide some additional functionality.  Please note that the
-file formats created by ``gdbm`` and ``dbm`` are incompatible.
+file formats created by :mod:`dbm.gnu` and :mod:`dbm.ndbm` are incompatible.
 
 The :mod:`dbm.gnu` module provides an interface to the GNU DBM library.
-``gdbm`` objects behave like mappings (dictionaries), except that keys and
-values are always strings.  Printing a :mod:`dbm.gnu` object doesn't print the
+``dbm.gnu.gdbm`` objects behave like mappings (dictionaries), except that keys and
+values are always converted to bytes before storing.  Printing a ``gdbm``
+object doesn't print the
 keys and values, and the :meth:`items` and :meth:`values` methods are not
 supported.
 
 .. exception:: error
 
-   Raised on ``gdbm``\ -specific errors, such as I/O errors. :exc:`KeyError` is
+   Raised on :mod:`dbm.gnu`-specific errors, such as I/O errors. :exc:`KeyError` is
    raised for general mapping errors like specifying an incorrect key.
 
 
@@ -183,7 +192,7 @@ supported.
 
       If you have carried out a lot of deletions and would like to shrink the space
       used by the ``gdbm`` file, this routine will reorganize the database.  ``gdbm``
-      will not shorten the length of a database file except by using this
+      objects will not shorten the length of a database file except by using this
       reorganization; otherwise, deleted file space will be kept and reused as new
       (key, value) pairs are added.
 
@@ -203,8 +212,8 @@ supported.
 
 The :mod:`dbm.ndbm` module provides an interface to the Unix "(n)dbm" library.
 Dbm objects behave like mappings (dictionaries), except that keys and values are
-always strings. Printing a dbm object doesn't print the keys and values, and the
-:meth:`items` and :meth:`values` methods are not supported.
+always stored as bytes. Printing a ``dbm`` object doesn't print the keys and
+values, and the :meth:`items` and :meth:`values` methods are not supported.
 
 This module can be used with the "classic" ndbm interface, the BSD DB
 compatibility interface, or the GNU GDBM compatibility interface. On Unix, the
@@ -213,7 +222,7 @@ to simplify building this module.
 
 .. exception:: error
 
-   Raised on dbm-specific errors, such as I/O errors. :exc:`KeyError` is raised
+   Raised on :mod:`dbm.ndbm`-specific errors, such as I/O errors. :exc:`KeyError` is raised
    for general mapping errors like specifying an incorrect key.
 
 
@@ -224,7 +233,7 @@ to simplify building this module.
 
 .. function:: open(filename[, flag[, mode]])
 
-   Open a dbm database and return a dbm object.  The *filename* argument is the
+   Open a dbm database and return a ``dbm`` object.  The *filename* argument is the
    name of the database file (without the :file:`.dir` or :file:`.pag` extensions;
    note that the BSD DB implementation of the interface will append the extension
    :file:`.db` and only create one file).
@@ -264,27 +273,27 @@ to simplify building this module.
 .. note::
 
    The :mod:`dbm.dumb` module is intended as a last resort fallback for the
-   :mod:`dbm` module when no more robust module is available. The :mod:`dbm.dumb`
+   :mod:`dbm` module when a more robust module is not available. The :mod:`dbm.dumb`
    module is not written for speed and is not nearly as heavily used as the other
    database modules.
 
 The :mod:`dbm.dumb` module provides a persistent dictionary-like interface which
-is written entirely in Python.  Unlike other modules such as :mod:`gdbm` no
+is written entirely in Python.  Unlike other modules such as :mod:`dbm.gnu` no
 external library is required.  As with other persistent mappings, the keys and
-values must always be strings.
+values are always stored as bytes.
 
 The module defines the following:
 
 
 .. exception:: error
 
-   Raised on dbm.dumb-specific errors, such as I/O errors.  :exc:`KeyError` is
+   Raised on :mod:`dbm.dumb`-specific errors, such as I/O errors.  :exc:`KeyError` is
    raised for general mapping errors like specifying an incorrect key.
 
 
 .. function:: open(filename[, flag[, mode]])
 
-   Open a dumbdbm database and return a dumbdbm object.  The *filename* argument is
+   Open a ``dumbdbm`` database and return a dumbdbm object.  The *filename* argument is
    the basename of the database file (without any specific extensions).  When a
    dumbdbm database is created, files with :file:`.dat` and :file:`.dir` extensions
    are created.