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Extensive changes by AMK.
author Guido van Rossum <guido@python.org>
date Thu, 17 Jul 1997 16:29:42 +0000
parents c6fe80ce7c20
children 4887d754692a
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5816:6a0d7cf19d38 5817:48b94de85bf3
1 \section{Built-in Module \sectcode{gdbm}} 1 \section{Built-in Module \sectcode{gdbm}}
2 \label{module-gdbm}
2 \bimodindex{gdbm} 3 \bimodindex{gdbm}
3 4
4 This module is nearly identical to the \code{dbm} module, but uses 5 This module is quite similar to the \code{dbm} module, but uses {\sc gdbm}
5 GDBM instead. Its interface is identical, and not repeated here. 6 instead to provide some additional functionality. Please note that
7 the file formats created by {\sc gdbm} and dbm are incompatible.
8 \bimodindex{dbm}
6 9
7 Warning: the file formats created by gdbm and dbm are incompatible. 10 The \code{gdbm} module provides an interface to the GNU DBM
8 \bimodindex{dbm} 11 library. {\sc gdbm} objects behave like mappings
12 (dictionaries), except that keys and values are always strings.
13 Printing a {\sc gdbm} object doesn't print the keys and values, and the
14 \code{items()} and \code{values()} methods are not supported.
15
16 The module defines the following constant and functions:
17
18 \renewcommand{\indexsubitem}{(in module dbm)}
19 \begin{excdesc}{error}
20 Raised on dbm-specific errors, such as I/O errors. \code{KeyError} is
21 raised for general mapping errors like specifying an incorrect key.
22 \end{excdesc}
23
24 \begin{funcdesc}{open}{filename\, \optional{flag\, \optional{mode}}}
25 Open a dbm database and return a dbm object. The \var{filename}
26 argument is the name of the database file (without the \file{.dir} or
27 \file{.pag} extensions).
28
29 The optional \var{flag} argument can be
30 \code{'r'} (to open an existing database for reading only --- default),
31 \code{'w'} (to open an existing database for reading and writing),
32 \code{'c'} (which creates the database if it doesn't exist), or
33 \code{'n'} (which always creates a new empty database).
34
35 Appending \code{f} to the flag opens the database in fast mode;
36 altered data will not automatically be written to the disk after every
37 change. This results in faster writes to the database, but may result
38 in an inconsistent database if the program crashes while the database
39 is still open. Use the \code{sync()} method to force any unwritten
40 data to be written to the disk.
41
42 The optional \var{mode} argument is the \UNIX{} mode of the file, used
43 only when the database has to be created. It defaults to octal
44 \code{0666}.
45 \end{funcdesc}
46
47 In addition to the dictionary-like methods, {\sc gdbm} objects have the
48 following methods:
49
50 \begin{funcdesc}{firstkey}{}
51 It's possible to loop over every key in the database using this method
52 and the \code{nextkey()} method. The traversal is ordered by {\sc gdbm}'s
53 internal hash values, and won't be sorted by the key values. This
54 method returns the starting key.
55 \end{funcdesc}
56
57 \begin{funcdesc}{nextkey}{key}
58 Returns the key that follows \var{key} in the traversal. The
59 following code prints every key in the database \code{db}, without having to
60 create a list in memory that contains them all:
61 \bcode\begin{verbatim}
62 k=db.firstkey()
63 while k!=None:
64 print k
65 k=db.nextkey(k)
66 \end{verbatim}\ecode
67 \end{funcdesc}
68
69 \begin{funcdesc}{reorganize}{}
70 If you have carried out a lot of deletions and would like to shrink
71 the space used by the {\sc gdbm} file, this routine will reorganize the
72 database. {\sc gdbm} will not shorten the length of a database file except
73 by using this reorganization; otherwise, deleted file space will be
74 kept and reused as new (key,value) pairs are added.
75 \end{funcdesc}
76
77 \begin{funcdesc}{sync}{}
78 When the database has been opened in fast mode, this method forces any
79 unwritten data to be written to the disk.
80 \end{funcdesc}
81