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<!DOCTYPE linuxdoc system>
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<article>
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<title>MySQLdb: a Python interface for MySQL
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<author>Andy Dustman
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<date>$Id$
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<abstract>MySQLdb is an thread-compatible interface to the popular
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MySQL database server that provides the Python database API.
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<sect>Introduction
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<P>This module should be <ref id="MySQLmodule" name="mostly compatible">
|
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with an older interface
|
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written by Joe Skinner and others. However, the older version is a)
|
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not thread-friendly (database operations could cause all other threads
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to block), b) written for MySQL 3.21 (does not compile against newer
|
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versions without patches), c) apparently not actively
|
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maintained. MySQLdb is a completely new module, distributed free of
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charge under a license derived from the Python license.
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<p>
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<sect1>Platforms
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<p>
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<sect2>Linux/UNIX
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<p>
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This module is developed on RedHat Linux 5.2 for Intel. It should build without
|
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much trouble on most UNIX-like platforms by using the <tt/build.py/ script.
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<sect2>Windows (3.11, 95, 98, NT, 2000, CE, BSOD, XYZ, etc.)
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<p>
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Windows is <em/not/ a supported platform.
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However, the <tt/compile.py/ script
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reportedly gets the job done, probably just on NT, maybe others.
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<sect1>Python
|
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<p>
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MySQLdb requires Python 1.5.2. Earlier versions will not work, because
|
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support for C <tt/long long/ is required by MySQL. If you have an
|
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earlier version of Python, upgrade to 1.5.2 or beyond.
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|
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<sect1>MySQL
|
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<p>
|
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<sect2>MySQL-3.22
|
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<p>
|
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Only versions 3.22.32 and
|
||||
up are guaranteed to work. Some older versions may work;
|
||||
if you have an older version you should
|
||||
seriously consider upgrading to get the bug fixes and particularly
|
||||
the security updates.
|
||||
|
||||
MySQL-3.22 seems to have a strange bug when handling TIME
|
||||
columns. For this reason, there is presently no type converter for
|
||||
TIME columns (the value is returned as a string). If you want to
|
||||
experiment with this, the code which actives the type converter can be
|
||||
easily commented in.
|
||||
|
||||
<sect2>MySQL-3.23
|
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<p>
|
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MySQLdb has only been lightly tested.
|
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MySQL-3.23 is presently in alpha (unstable) release. Several API
|
||||
additions have been made so far. These will be incorporated into
|
||||
MySQLdb as work progresses.
|
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|
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<sect1>DateTime
|
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<p>If you have the <htmlurl
|
||||
url="http://starship.skyport.net/~lemburg/mxDateTime.html"
|
||||
name="DateTime"> module installed (recommended), MySQLdb will use
|
||||
it for date-related objects. Otherwise, these will be returned to
|
||||
Python as strings. You can also modify the type conversion
|
||||
dictionaries to return these as other object classes, if you
|
||||
prefer.
|
||||
|
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<sect1>MySQLmodule<label id="MySQLmodule">
|
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<p>
|
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MySQLmodule, the older MySQL interface by Joe Skinner and others,
|
||||
is also a split C/Python
|
||||
interface. <tt/MySQL/, the C portion, has an interface similar to
|
||||
perl's DBI internally. In addition, there is Python portion, <tt/Mysqldb/,
|
||||
which provides a DB API v1.0 interface, written by James Henstridge.
|
||||
|
||||
In contrast, MySQLdb's C portion, <tt><ref id="_mysql"></tt>, is designed
|
||||
to mimic the MySQL C API in an object-oriented way; you should not
|
||||
expect to move from <tt/MySQL/ to <tt/_mysql/ without a fair amount of
|
||||
work. <tt><ref id="MySQLdb"></tt> provides a DB API v2.0 interface,
|
||||
which has some changes from the v1.0 interface. Things to watch out
|
||||
for in particular:
|
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|
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<table>
|
||||
<tabular ca="foo">
|
||||
Operation | Mysqldb | MySQLdb
|
||||
@ Connecting | <tt>db = Mysqldb.Mysqldb("db@host user pass")</tt>
|
||||
| <tt>db = MySQLdb.connect(db='db', host='host', user='user', passwd='pass')</tt>
|
||||
@ Implicit cursor | <tt>db.execute(SQL)</tt> |
|
||||
implicit cursors dropped from DB API v2.0; always use <tt>c = db.cursor()</tt>
|
||||
@ Fetch row as dictionary | <tt>c.fetchDict()</tt>,
|
||||
keys are "<em/table.column/" |
|
||||
not standard; <tt>MySQLDict.py</tt> provides a dictionary interface,
|
||||
keys are "<em/column/"; use SQL <tt/AS/ to rename fields.
|
||||
@ Transactions | <tt>db.commit()</tt> and <tt>db.rollback()</tt>
|
||||
both exist and silently do nothing <ref id="rollback" name="(danger!)">
|
||||
| <tt>db.commit()</tt> and <tt>db.rollback()</tt> work if the MySQL
|
||||
client library can perform transactions; otherwise <tt>db.rollback()</tt>
|
||||
is not defined
|
||||
<caption>Mysqldb to MySQLdb changes</tabular></table>
|
||||
|
||||
<sect1>Zope and ZMySQLDA
|
||||
<p>The distribution contains a patch to modify the
|
||||
<htmlurl url="http://www.zope.org/" name="Zope">
|
||||
<htmlurl url="http://www.zope.org/Members/MikeP/ZMySQLDA" name="ZMySQLDA">
|
||||
to use MySQLdb instead of MySQLmodule. Read the instructions in
|
||||
the patch. If that fails, read the FAQ.
|
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<sect1>Documentation
|
||||
<p>The web page documentation may be slightly ahead of the latest release
|
||||
and may reflect features of the next release.
|
||||
<sect1>FAQs
|
||||
<p>A FAQ is available at
|
||||
<htmlurl url="http://starship.python.net/crew/adustman/MySQLdb-FAQ.html">.
|
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<sect>_mysql module<label id="_mysql">
|
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<P>
|
||||
If you want to write applications which are portable across databases,
|
||||
avoid using this module directly. <tt>_mysql</tt> provides an
|
||||
interface which mostly implements the MySQL C API. For more
|
||||
information, see the MySQL documentation. The documentation for this
|
||||
module is intentionally weak because you probably should use the
|
||||
higher-level <ref id="MySQLdb"> module. If you really need it, use the
|
||||
standard MySQL docs and transliterate as necessary.
|
||||
<p>
|
||||
The C API has been wrapped in an object-oriented way. The only MySQL
|
||||
data structures which are implemented are the <tt>MYSQL</tt> (database
|
||||
connection handle) and <tt>MYSQL_RES</tt> (result handle) types. In
|
||||
general, any function which takes <tt>MYSQL *mysql</tt> as an argument
|
||||
is now a method of the connection object, and any function which takes
|
||||
<tt>MYSQL_RES *result</tt> as an argument is a method of the result
|
||||
object. Functions requiring none of the MySQL data structures are
|
||||
implemented as functions in the module. Functions requiring one of the
|
||||
other MySQL data structures are generally not implemented. Deprecated
|
||||
functions are not implemented. In all cases, the <tt>mysql_</tt>
|
||||
prefix is dropped from the name. Most of the <tt>conn</tt> methods
|
||||
listed are also available as MySQLdb Connection object methods. Their
|
||||
use is explicitly non-portable.
|
||||
<table>
|
||||
<tabular ca="MySQL C API foo foo function mapping">
|
||||
C API | <tt>_mysql</tt>
|
||||
@ <tt>mysql_affected_rows()</tt> | <tt>conn.affected_rows()</tt>
|
||||
@ <tt>mysql_close()</tt> | <tt>conn.close()</tt>
|
||||
@ <tt>mysql_connect()</tt> | <tt>_mysql.connect()</tt>
|
||||
@ <tt>mysql_data_seek()</tt> | <tt>result.data_seek()</tt>
|
||||
@ <tt>mysql_debug()</tt> | <tt>_mysql.debug()</tt>
|
||||
@ <tt>mysql_dump_debug_info</tt> | <tt>conn.dump_debug_info()</tt>
|
||||
@ <tt>mysql_escape_string()</tt> | <tt>_mysql.escape_string()</tt>
|
||||
@ <tt>mysql_fetch_row()</tt> | <tt>result.fetch_row()<newline>
|
||||
result_fetch_row_as_dict()<newline>
|
||||
result.fetch_rows()<newline>
|
||||
result.fetch_rows_as_dict()<newline>
|
||||
result.fetch_all_rows()<newline>
|
||||
result.fetch_all_rows_as_dict()</tt>
|
||||
@ <tt>mysql_get_client_info()</tt> | <tt>_mysql.get_client_info()</tt>
|
||||
@ <tt>mysql_get_host_info()</tt> | <tt>conn.get_host_info()</tt>
|
||||
@ <tt>mysql_get_proto_info()</tt> | <tt>conn.get_proto_info()</tt>
|
||||
@ <tt>mysql_get_server_info()</tt> | <tt>conn.get_server_info()</tt>
|
||||
@ <tt>mysql_info()</tt> | <tt>conn.info()</tt>
|
||||
@ <tt>mysql_insert_id()</tt> | <tt>conn.insert_id()</tt>
|
||||
@ <tt>mysql_list_dbs()</tt> | <tt>conn.list_dbs()</tt>
|
||||
@ <tt>mysql_list_fields()</tt> | <tt>conn.list_fields()</tt>
|
||||
@ <tt>mysql_list_processes()</tt> | <tt>conn.list_processes()</tt>
|
||||
@ <tt>mysql_list_tables()</tt> | <tt>conn.list_tables()</tt>
|
||||
@ <tt>mysql_num_fields()</tt> | <tt>result.num_fields()</tt>
|
||||
@ <tt>mysql_num_rows()</tt> | <tt>result.num_rows()</tt>
|
||||
@ <tt>mysql_ping()</tt> | <tt>conn.ping()</tt>
|
||||
@ <tt>mysql_query()</tt> | <tt>conn.query()</tt>
|
||||
@ <tt>mysql_real_connect()</tt> | <tt>_mysql.connect()</tt>
|
||||
@ <tt>mysql_real_query()</tt> | <tt>conn.query()</tt>
|
||||
@ <tt>mysql_row_seek()</tt> | <tt>result.row_seek()</tt>
|
||||
@ <tt>mysql_row_tell()</tt> | <tt>result.row_tell()</tt>
|
||||
@ <tt>mysql_select_db()</tt> | <tt>conn.select_db()</tt>
|
||||
@ <tt>mysql_stat()</tt> | <tt>conn.stat()</tt>
|
||||
@ <tt>mysql_store_result()</tt> | <tt>conn.store_result()</tt>
|
||||
@ <tt>mysql_thread_id()</tt> | <tt>conn.thread_id()</tt>
|
||||
@ <tt>mysql_use_result()</tt> | <tt>conn.use_result()</tt>
|
||||
@ <tt>CLIENT_*</tt> | <tt>_mysql.CLIENT.*</tt>
|
||||
@ <tt>CR_*</tt> | <tt>_mysql.CR.*</tt>
|
||||
@ <tt>ER_*</tt> | <tt>_mysql.ER.*</tt>
|
||||
@ <tt>FIELD_TYPE_*</tt> | <tt>_mysql.FIELD_TYPE.*</tt>
|
||||
@ <tt>FLAG_*</tt> | <tt>_mysql.FLAG.*</tt>
|
||||
<caption>MySQL C API function mapping
|
||||
</tabular>
|
||||
</table>
|
||||
<sect>MySQLdb -- DB API interface<label id="MySQLdb">
|
||||
<p>
|
||||
MySQLdb is a thin Python wrapper around <tt><ref id="_mysql"></tt>
|
||||
which makes it compatible with the Python DB API interface (version
|
||||
2). In reality, a fair amount of the code which implements the API is
|
||||
in <tt>_mysql</tt> for the sake of efficiency.
|
||||
<p>
|
||||
The DB API specification should be your primary guide for using this
|
||||
module. Only deviations from the spec and other database-dependent
|
||||
things will be documented here. Note that all symbols from
|
||||
<tt>_mysql</tt> are imported into this module. Mostly these are the
|
||||
required exceptions, the constant classes, and a very few functions.
|
||||
<sect1>Functions and attributes <P>Only a few top-level functions and
|
||||
attributes are defined within MySQLdb.
|
||||
|
||||
<descrip>
|
||||
<tag><label id="connect()">connect(parameters...)</tag> Constructor
|
||||
for creating a connection to the database. Returns a Connection
|
||||
Object. Parameters are the same as for the MySQL C API. Note
|
||||
that all parameters must be specified as keyword arguments! The
|
||||
default value for each parameter is NULL or zero, as
|
||||
appropriate. Consult the MySQL documentation for more
|
||||
details. The important parameters are:
|
||||
|
||||
<descrip>
|
||||
<tag>host</tag>
|
||||
name of host to connect to. Default: use local host
|
||||
|
||||
<tag>user</tag>
|
||||
user to authenticate as. Default: current effective user.
|
||||
|
||||
<tag>passwd</tag>
|
||||
password to authenticate with. Default: no password.
|
||||
|
||||
<tag>db</tag>
|
||||
database to use. Default: no default database.
|
||||
|
||||
<tag>conv</tag> literal-to-Python type conversion dictionary.
|
||||
Default: empty dictionary, no type conversion.
|
||||
|
||||
<tag>quote_conv</tag> Python type-to-literal conversion
|
||||
dictionary Default: empty dictionary, no type conversion.
|
||||
|
||||
<tag>unix_pipe</tag>
|
||||
location of UNIX socket. Default: use TCP.
|
||||
|
||||
<tag>port</tag>
|
||||
TCP port of MySQL server. Default: standard port (3306).
|
||||
</descrip>
|
||||
|
||||
<tag>apilevel</tag>
|
||||
String constant stating the supported DB API level. '2.0'
|
||||
|
||||
<tag>threadsafety</tag> Integer constant stating the level of thread
|
||||
safety the interface supports. Set to 1, which means: Threads
|
||||
may share the module, but not connections. This is the practice
|
||||
recommended by the MySQL documentation. However, it should be
|
||||
safe to share a connection between two threads provided only one
|
||||
thread at a time uses it (i.e. a mutex is employed). Note that
|
||||
this is only safe if the threads are using. mysql_store_result()
|
||||
as opposed to mysql_use_result(). The latter is not recommended
|
||||
for threaded applications. See the MySQL documentation for more
|
||||
details.
|
||||
|
||||
<tag>paramstyle</tag> String constant stating the type of parameter
|
||||
marker formatting expected by the interface. Set to 'format' =
|
||||
ANSI C printf format codes, e.g. '...WHERE name=%s'. If a
|
||||
mapping object is used for conn.execute(), then the interface
|
||||
actually uses 'pyformat' = Python extended format codes,
|
||||
e.g. '...WHERE name=%(name)s'. However, the API does not
|
||||
presently allow the specification of more than one style in
|
||||
paramstyle.
|
||||
|
||||
Compatibility note: The older MySQLmodule uses a similar
|
||||
parameter scheme, but requires that quotes be placed around
|
||||
format strings which will contain strings, dates, and similar
|
||||
character data. This is not necessary for MySQLdb. It is
|
||||
recommended that %s (and not '%s') be used for all parameters,
|
||||
regardless of type. The interface performs all necessary
|
||||
quoting.
|
||||
|
||||
<tag><label id="type_conv">type_conv</tag> A dictionary mapping MySQL
|
||||
types (from <TT>FIELD_TYPE.*</TT>) to callable Python objects
|
||||
(usually functions) which convert from a string to the desired
|
||||
type. This is initialized with reasonable defaults for most
|
||||
types. When creating a Connection object, you can pass your own
|
||||
type converter dictionary as a keyword parameter. Otherwise, it
|
||||
uses a copy of <tt>type_conv</tt> which is safe to modify on a
|
||||
per-connection basis. The dictionary includes some of the
|
||||
factory functions from the <tt>DateTime</tt> module, if it is
|
||||
available. Several non-standard types (<tt>SET, ENUM</tt>) are
|
||||
returned as strings, which is how MySQL returns all
|
||||
columns. Note: <tt>TIME</tt> columns are returned as strings
|
||||
presently. This should be a temporary condition.
|
||||
|
||||
<tag><label id="quote_conv">quote_conv</tag> A dictionary mapping
|
||||
Python types (from the standard <tt>types</tt> module or
|
||||
built-in function <tt>type()</tt> to MySQL literals. By
|
||||
default, the value is treated as a string. When creating a
|
||||
Connection object, you can pass your own quote converter
|
||||
dictionary as a keyword parameter.
|
||||
|
||||
</descrip>
|
||||
|
||||
<sect1>Connection Objects
|
||||
<P>Connection objects are returned by the <tt>connect()</tt> function.
|
||||
<descrip>
|
||||
<tag>commit()</tag> If the database supports transactions, this
|
||||
commits the current transaction; otherwise this method
|
||||
successfully does nothing. <footnote>MySQL does not presently
|
||||
support transactions.</footnote>
|
||||
|
||||
<tag><label id="rollback">rollback()</tag> If the
|
||||
database supports transactions, this rolls back (cancels) the
|
||||
current transaction; otherwise a <tt>NotSupportedError</tt> is
|
||||
raised. This method is only defined if the MySQL client library
|
||||
supports transactions.
|
||||
|
||||
Compatibility note: The older <ref id="MySQLmodule"> does define this method,
|
||||
which sucessfully does nothing. This is dangerous behavior, as a
|
||||
successful rollback indicates that the current transaction was
|
||||
backed out, which is not true, and fails to notify the
|
||||
programmer that the database now needs to be cleaned up by other
|
||||
means.
|
||||
|
||||
<tag>cursor(parameters...)</tag>
|
||||
MySQL does not support cursors; however, cursors are easily emulated.
|
||||
</descrip>
|
||||
|
||||
<sect1>Cursor Objects
|
||||
<P>Cursor objects support an optional argument
|
||||
<tt>name</tt>, which is pretty useless. While it is possible to
|
||||
create Cursor objects with the class constructor, this is not
|
||||
recommended.
|
||||
<p>
|
||||
<descrip>
|
||||
<tag>callproc()</tag>
|
||||
Not implemented.
|
||||
|
||||
<tag>nextset()</tag>
|
||||
Not implemented.
|
||||
|
||||
<tag>setinputsizes()</tag>
|
||||
Does nothing, successfully.
|
||||
|
||||
<tag>setoutputsizes()</tag>
|
||||
Does nothing, successfully.
|
||||
|
||||
<tag><label id="executeXXX()">execute(query[,parameters]></tag>
|
||||
|
||||
<tag>executemany(query,[,parameters])</tag> These methods work as
|
||||
described in the API. The parameters are converted according to
|
||||
the <ref id="quote_conv"> dictionary (see above). By default,
|
||||
<tt>str()</tt> is used as the conversion function. This presents
|
||||
a problem for the various date and time columns:
|
||||
<tt>__str__</tt> for <tt>DateTime</tt> objects includes
|
||||
fractional seconds, which MySQL (up to 3.22.32, at least),
|
||||
considers illegal input, and so zeros the field. This may be
|
||||
fixed in later MySQL releases.
|
||||
|
||||
<tag>fetchone()</tag>
|
||||
|
||||
<tag>fetchmany([n])</tag>
|
||||
|
||||
<tag>fetchall()</tag>
|
||||
These methods work as described in the API.
|
||||
|
||||
<tag>format_DATE(d)</tag>
|
||||
|
||||
<tag>format_TIME(d)</tag>
|
||||
|
||||
<tag>format_TIMESTAMP(d)</tag> These functions all take a DateTime
|
||||
object as input and return an appropriately formatted
|
||||
string. They are intended for use with the <tt><ref
|
||||
id="executeXXX()"></tt> methods.
|
||||
|
||||
</descrip>
|
||||
<sect>Using and extending
|
||||
|
||||
<P>In general, it is probably wise to not directly interact with the
|
||||
DB API except for small applicatons. Databases, even SQL databases,
|
||||
vary widely in capabilities and may have non-standard features. The DB
|
||||
API does a good job of providing a reasonably portable interface but
|
||||
some methods are non-portable. Specifically, the parameters accepted
|
||||
by <tt><ref id="connect()"></tt> are completely implementation-dependent.
|
||||
|
||||
If you believe your application may need to run on several different
|
||||
databases, the author recommends the following approach, based on
|
||||
personal experience: Write a simplified API for your application which
|
||||
implements the specific queries and operations your application needs
|
||||
to perform. Implement this API as a base class which should be have
|
||||
few database dependencies, and then derive a subclass from this which
|
||||
implements the necessary dependencies. In this way, porting your
|
||||
application to a new database should be a relatively simple matter of
|
||||
creating a new subclass, assuming the new database is reasonably
|
||||
standard.
|
||||
|
||||
For an example of this, see the author's
|
||||
<htmlurl url="http://starship.python.net/crew/adustman"
|
||||
name="SQLDict module">, which allows standard queries to be
|
||||
defined and accessed using an object which looks like a
|
||||
dictionary, and reads/writes user-defined objects.
|
||||
|
||||
Because MySQLdb's Connection and Cursor objects are written in Python,
|
||||
you can easily derive your own subclasses. There are several Cursor
|
||||
classes in MySQLdb:
|
||||
<p>
|
||||
<descrip>
|
||||
<tag>CursorBase</tag> The base class for Cursor objects.
|
||||
|
||||
<tag>CursorWarningMixIn</tag> Causes the Warning exception to be raised
|
||||
on queries which produce warnings.
|
||||
|
||||
<tag>CursorStoreResultMixIn</tag> Causes the Cursor to use the
|
||||
<tt>mysql_store_result()</tt> function to get the query result. The
|
||||
entire result set is stored on the client side.
|
||||
|
||||
<tag>CursorUseResultMixIn</tag> Causes the cursor to use the
|
||||
<tt>mysql_use_result()</tt> function to get the query result. The
|
||||
result set is stored on the server side and is transferred row by row
|
||||
using fetch operations. Not recommended, particularly for threaded
|
||||
applications.
|
||||
|
||||
<tag>CursorTupleRowsMixIn</tag> Causes the cursor to return rows
|
||||
as a tuple of the column values.
|
||||
|
||||
<tag>CursorDictRowsMixIn</tag> Causes the cursor to return rows
|
||||
as a dictionary, where the keys are column names and the values
|
||||
are column values. Note that if the column names are not unique,
|
||||
some of them will be overwritten. This can be avoided by using
|
||||
the SQL <tt>AS</TT> keyword. (This is yet-another reason not to use
|
||||
<tt/*/ in SQL queries, particularly where <tt/JOIN/ is involved.
|
||||
|
||||
<tag>Cursor</tag> The default cursor class. This class is composed
|
||||
of <tt>CursorWarningMixIn, CursorStoreResultMixIn, CursorTupleRowsMixIn,</tt>
|
||||
and <tt>BaseCursor</tt>, i.e. it raises <tt>Warning</tt>, uses
|
||||
<tt>mysql_store_result()</tt>, and returns rows as tuples.
|
||||
</descrip>
|
||||
<p>For an example of how to use these classes, take a look at the
|
||||
<tt>MySQLDict</tt> module, which comes with MySQLdb.
|
||||
This operates as above, except that it
|
||||
returns rows as dictionaries.
|
||||
|
||||
</article>
|
||||
|
||||
|
||||
|
||||
Reference in New Issue
Block a user