From 7a846cf5e35ebcad852309aebaa0bac8a7244744 Mon Sep 17 00:00:00 2001 From: Evax Software Date: Thu, 4 Oct 2012 13:34:39 -0400 Subject: Allow pip install from git Merged with modifications from https://github.com/evax/MySQLdb1/commit/a8152690101733904b16a32ff8467220ca07242c --- doc/FAQ.txt | 143 +++++++++++ doc/MySQLdb.txt | 718 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 861 insertions(+) create mode 100644 doc/FAQ.txt create mode 100644 doc/MySQLdb.txt (limited to 'doc') diff --git a/doc/FAQ.txt b/doc/FAQ.txt new file mode 100644 index 0000000..b6a4ce9 --- /dev/null +++ b/doc/FAQ.txt @@ -0,0 +1,143 @@ +==================================== + MySQLdb Frequently Asked Questions +==================================== + +.. contents:: +.. + + +Build Errors +------------ + + ld: fatal: library -lmysqlclient_r: not found + +mysqlclient_r is the thread-safe library. It's not available on +all platforms, or all installations, apparently. You'll need to +reconfigure site.cfg (in MySQLdb-1.2.1 and newer) to have +threadsafe = False. + + mysql.h: No such file or directory + +This almost always mean you don't have development packages +installed. On some systems, C headers for various things (like MySQL) +are distributed as a seperate package. You'll need to figure out +what that is and install it, but often the name ends with -devel. + +Another possibility: Some older versions of mysql_config behave oddly +and may throw quotes around some of the path names, which confused +MySQLdb-1.2.0. 1.2.1 works around these problems. If you see things +like -I'/usr/local/include/mysql' in your compile command, that's +probably the issue, but it shouldn't happen any more. + + +ImportError +----------- + + ImportError: No module named _mysql + +If you see this, it's likely you did some wrong when installing +MySQLdb; re-read (or read) README. _mysql is the low-level C module +that interfaces with the MySQL client library. + +Various versions of MySQLdb in the past have had build issues on +"weird" platforms; "weird" in this case means "not Linux", though +generally there aren't problems on Unix/POSIX platforms, including +BSDs and Mac OS X. Windows has been more problematic, in part because +there is no `mysql_config` available in the Windows installation of +MySQL. 1.2.1 solves most, if not all, of these problems, but you will +still have to edit a configuration file so that the setup knows where +to find MySQL and what libraries to include. + + + ImportError: libmysqlclient_r.so.14: cannot open shared object file: No such file or directory + +The number after .so may vary, but this means you have a version of +MySQLdb compiled against one version of MySQL, and are now trying to +run it against a different version. The shared library version tends +to change between major releases. + +Solution: Rebuilt MySQLdb, or get the matching version of MySQL. + +Another thing that can cause this: The MySQL libraries may not be on +your system path. + +Solutions: + +* set the LD_LIBRARY_PATH environment variable so that it includes + the path to the MySQL libraries. + +* set static=True in site.cfg for static linking + +* reconfigure your system so that the MySQL libraries are on the + default loader path. In Linux, you edit /etc/ld.so.conf and run + ldconfig. For Solaris, see `Linker and Libraries Guide + `_. + + + ImportError: ld.so.1: python: fatal: libmtmalloc.so.1: DF_1_NOOPEN tagged object may not be dlopen()'ed + +This is a weird one from Solaris. What does it mean? I have no idea. +However, things like this can happen if there is some sort of a compiler +or environment mismatch between Python and MySQL. For example, on some +commercial systems, you might have some code compiled with their own +compiler, and other things compiled with GCC. They don't always mesh +together. One way to encounter this is by getting binary packages from +different vendors. + +Solution: Rebuild Python or MySQL (or maybe both) from source. + + ImportError: dlopen(./_mysql.so, 2): Symbol not found: _sprintf$LDBLStub + Referenced from: ./_mysql.so + Expected in: dynamic lookup + +This is one from Mac OS X. It seems to have been a compiler mismatch, +but this time between two different versions of GCC. It seems nearly +every major release of GCC changes the ABI in some why, so linking +code compiled with GCC-3.3 and GCC-4.0, for example, can be +problematic. + + +My data disappeared! (or won't go away!) +---------------------------------------- + +Starting with 1.2.0, MySQLdb disables autocommit by default, as +required by the DB-API standard (`PEP-249`_). If you are using InnoDB +tables or some other type of transactional table type, you'll need +to do connection.commit() before closing the connection, or else +none of your changes will be written to the database. + +Conversely, you can also use connection.rollback() to throw away +any changes you've made since the last commit. + +Important note: Some SQL statements -- specifically DDL statements +like CREATE TABLE -- are non-transactional, so they can't be +rolled back, and they cause pending transactions to commit. + + +Other Errors +------------ + + OperationalError: (1251, 'Client does not support authentication protocol requested by server; consider upgrading MySQL client') + +This means your server and client libraries are not the same version. +More specifically, it probably means you have a 4.1 or newer server +and 4.0 or older client. You can either upgrade the client side, or +try some of the workarounds in `Password Hashing as of MySQL 4.1 +`_. + + +Other Resources +--------------- + +* Help forum. Please search before posting. + +* `Google `_ + +* READ README! + +* Read the User's Guide + +* Read `PEP-249`_ + +.. _`PEP-249`: http://www.python.org/peps/pep-0249.html + diff --git a/doc/MySQLdb.txt b/doc/MySQLdb.txt new file mode 100644 index 0000000..fbc86e5 --- /dev/null +++ b/doc/MySQLdb.txt @@ -0,0 +1,718 @@ +==================== +MySQLdb User's Guide +==================== + +.. contents:: +.. + +Introduction +------------ + +MySQLdb is an thread-compatible interface to the popular MySQL +database server that provides the Python database API. + +Installation +------------ + +The ``README`` file has complete installation instructions. + + +_mysql +------ + +If you want to write applications which are portable across databases, +use MySQLdb_, and avoid using this module directly. ``_mysql`` +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 MySQLdb module. If you really need it, use the +standard MySQL docs and transliterate as necessary. + +.. _`MySQL documentation`: http://dev.mysql.com/doc/ + + +MySQL C API translation +....................... + +The MySQL C API has been wrapped in an object-oriented way. The only +MySQL data structures which are implemented are the ``MYSQL`` +(database connection handle) and ``MYSQL_RES`` (result handle) +types. In general, any function which takes ``MYSQL *mysql`` as an +argument is now a method of the connection object, and any function +which takes ``MYSQL_RES *result`` 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 ``mysql_`` +prefix is dropped from the name. Most of the ``conn`` methods listed +are also available as MySQLdb Connection object methods. Their use is +non-portable. + +MySQL C API function mapping +............................ + +=================================== ================================== + C API ``_mysql`` +=================================== ================================== + ``mysql_affected_rows()`` ``conn.affected_rows()`` + ``mysql_autocommit()`` ``conn.autocommit()`` + ``mysql_character_set_name()`` ``conn.character_set_name()`` + ``mysql_close()`` ``conn.close()`` + ``mysql_commit()`` ``conn.commit()`` + ``mysql_connect()`` ``_mysql.connect()`` + ``mysql_data_seek()`` ``result.data_seek()`` + ``mysql_debug()`` ``_mysql.debug()`` + ``mysql_dump_debug_info`` ``conn.dump_debug_info()`` + ``mysql_escape_string()`` ``_mysql.escape_string()`` + ``mysql_fetch_row()`` ``result.fetch_row()`` + ``mysql_get_character_set_info()`` ``conn.get_character_set_info()`` + ``mysql_get_client_info()`` ``_mysql.get_client_info()`` + ``mysql_get_host_info()`` ``conn.get_host_info()`` + ``mysql_get_proto_info()`` ``conn.get_proto_info()`` + ``mysql_get_server_info()`` ``conn.get_server_info()`` + ``mysql_info()`` ``conn.info()`` + ``mysql_insert_id()`` ``conn.insert_id()`` + ``mysql_num_fields()`` ``result.num_fields()`` + ``mysql_num_rows()`` ``result.num_rows()`` + ``mysql_options()`` various options to ``_mysql.connect()`` + ``mysql_ping()`` ``conn.ping()`` + ``mysql_query()`` ``conn.query()`` + ``mysql_real_connect()`` ``_mysql.connect()`` + ``mysql_real_query()`` ``conn.query()`` + ``mysql_real_escape_string()`` ``conn.escape_string()`` + ``mysql_rollback()`` ``conn.rollback()`` + ``mysql_row_seek()`` ``result.row_seek()`` + ``mysql_row_tell()`` ``result.row_tell()`` + ``mysql_select_db()`` ``conn.select_db()`` + ``mysql_set_character_set()`` ``conn.set_character_set()`` + ``mysql_ssl_set()`` ``ssl`` option to ``_mysql.connect()`` + ``mysql_stat()`` ``conn.stat()`` + ``mysql_store_result()`` ``conn.store_result()`` + ``mysql_thread_id()`` ``conn.thread_id()`` + ``mysql_thread_safe_client()`` ``conn.thread_safe_client()`` + ``mysql_use_result()`` ``conn.use_result()`` + ``mysql_warning_count()`` ``conn.warning_count()`` + ``CLIENT_*`` ``MySQLdb.constants.CLIENT.*`` + ``CR_*`` ``MySQLdb.constants.CR.*`` + ``ER_*`` ``MySQLdb.constants.ER.*`` + ``FIELD_TYPE_*`` ``MySQLdb.constants.FIELD_TYPE.*`` + ``FLAG_*`` ``MySQLdb.constants.FLAG.*`` +=================================== ================================== + + +Some _mysql examples +.................... + +Okay, so you want to use ``_mysql`` anyway. Here are some examples. + +The simplest possible database connection is:: + + import _mysql + db=_mysql.connect() + +This creates a connection to the MySQL server running on the local +machine using the standard UNIX socket (or named pipe on Windows), +your login name (from the USER environment variable), no password, and +does not ``USE`` a database. Chances are you need to supply more +information.:: + + db=_mysql.connect("localhost","joebob","moonpie","thangs") + +This creates a connection to the MySQL server running on the local +machine via a UNIX socket (or named pipe), the user name "joebob", the +password "moonpie", and selects the initial database "thangs". + +We haven't even begun to touch upon all the parameters ``connect()`` +can take. For this reason, I prefer to use keyword parameters:: + + db=_mysql.connect(host="localhost",user="joebob", + passwd="moonpie",db="thangs") + +This does exactly what the last example did, but is arguably easier to +read. But since the default host is "localhost", and if your login +name really was "joebob", you could shorten it to this:: + + db=_mysql.connect(passwd="moonpie",db="thangs") + +UNIX sockets and named pipes don't work over a network, so if you +specify a host other than localhost, TCP will be used, and you can +specify an odd port if you need to (the default port is 3306):: + + db=_mysql.connect(host="outhouse",port=3307,passwd="moonpie",db="thangs") + +If you really had to, you could connect to the local host with TCP by +specifying the full host name, or 127.0.0.1. + +Generally speaking, putting passwords in your code is not such a good +idea:: + + db=_mysql.connect(host="outhouse",db="thangs",read_default_file="~/.my.cnf") + +This does what the previous example does, but gets the username and +password and other parameters from ~/.my.cnf (UNIX-like systems). Read +about `option files`_ for more details. + +.. _`option files`: http://dev.mysql.com/doc/mysql/en/Option_files.html + +So now you have an open connection as ``db`` and want to do a +query. Well, there are no cursors in MySQL, and no parameter +substitution, so you have to pass a complete query string to +``db.query()``:: + + db.query("""SELECT spam, eggs, sausage FROM breakfast + WHERE price < 5""") + +There's no return value from this, but exceptions can be raised. The +exceptions are defined in a separate module, ``_mysql_exceptions``, +but ``_mysql`` exports them. Read DB API specification PEP-249_ to +find out what they are, or you can use the catch-all ``MySQLError``. + +.. _PEP-249: http://www.python.org/peps/pep-0249.html + +At this point your query has been executed and you need to get the +results. You have two options:: + + r=db.store_result() + # ...or... + r=db.use_result() + +Both methods return a result object. What's the difference? +``store_result()`` returns the entire result set to the client +immediately. If your result set is really large, this could be a +problem. One way around this is to add a ``LIMIT`` clause to your +query, to limit the number of rows returned. The other is to use +``use_result()``, which keeps the result set in the server and sends +it row-by-row when you fetch. This does, however, tie up server +resources, and it ties up the connection: You cannot do any more +queries until you have fetched **all** the rows. Generally I +recommend using ``store_result()`` unless your result set is really +huge and you can't use ``LIMIT`` for some reason. + +Now, for actually getting real results:: + + >>> r.fetch_row() + (('3','2','0'),) + +This might look a little odd. The first thing you should know is, +``fetch_row()`` takes some additional parameters. The first one is, +how many rows (``maxrows``) should be returned. By default, it returns +one row. It may return fewer rows than you asked for, but never +more. If you set ``maxrows=0``, it returns all rows of the result +set. If you ever get an empty tuple back, you ran out of rows. + +The second parameter (``how``) tells it how the row should be +represented. By default, it is zero which means, return as a tuple. +``how=1`` means, return it as a dictionary, where the keys are the +column names, or ``table.column`` if there are two columns with the +same name (say, from a join). ``how=2`` means the same as ``how=1`` +except that the keys are *always* ``table.column``; this is for +compatibility with the old ``Mysqldb`` module. + +OK, so why did we get a 1-tuple with a tuple inside? Because we +implicitly asked for one row, since we didn't specify ``maxrows``. + +The other oddity is: Assuming these are numeric columns, why are they +returned as strings? Because MySQL returns all data as strings and +expects you to convert it yourself. This would be a real pain in the +ass, but in fact, ``_mysql`` can do this for you. (And ``MySQLdb`` +does do this for you.) To have automatic type conversion done, you +need to create a type converter dictionary, and pass this to +``connect()`` as the ``conv`` keyword parameter. + +The keys of ``conv`` should be MySQL column types, which in the +C API are ``FIELD_TYPE_*``. You can get these values like this:: + + from MySQLdb.constants import FIELD_TYPE + +By default, any column type that can't be found in ``conv`` is +returned as a string, which works for a lot of stuff. For our +purposes, we probably want this:: + + my_conv = { FIELD_TYPE.LONG: int } + +This means, if it's a ``FIELD_TYPE_LONG``, call the builtin ``int()`` +function on it. Note that ``FIELD_TYPE_LONG`` is an ``INTEGER`` +column, which corresponds to a C ``long``, which is also the type used +for a normal Python integer. But beware: If it's really an ``UNSIGNED +INTEGER`` column, this could cause overflows. For this reason, +``MySQLdb`` actually uses ``long()`` to do the conversion. But we'll +ignore this potential problem for now. + +Then if you use ``db=_mysql.connect(conv=my_conv...)``, the +results will come back ``((3, 2, 0),)``, which is what you would +expect. + +MySQLdb +------- + +MySQLdb is a thin Python wrapper around ``_mysql`` 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 ``_mysql`` +for the sake of efficiency. + +The DB API specification PEP-249_ should be your primary guide for +using this module. Only deviations from the spec and other +database-dependent things will be documented here. + +Functions and attributes +........................ + +Only a few top-level functions and attributes are defined within +MySQLdb. + +connect(parameters...) + Constructor for creating a connection to the + database. Returns a Connection Object. Parameters are the + same as for the MySQL C API. In addition, there are a few + additional keywords that correspond to what you would pass + ``mysql_options()`` before connecting. Note that some + 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: + + host + name of host to connect to. Default: use the local host + via a UNIX socket (where applicable) + + user + user to authenticate as. Default: current effective user. + + passwd + password to authenticate with. Default: no password. + + db + database to use. Default: no default database. + + port + TCP port of MySQL server. Default: standard port (3306). + + unix_socket + location of UNIX socket. Default: use default location or + TCP for remote hosts. + + conv + type conversion dictionary. Default: a copy of + ``MySQLdb.converters.conversions`` + + compress + Enable protocol compression. Default: no compression. + + connect_timeout + Abort if connect is not completed within + given number of seconds. Default: no timeout (?) + + named_pipe + Use a named pipe (Windows). Default: don't. + + init_command + Initial command to issue to server upon + connection. Default: Nothing. + + read_default_file + MySQL configuration file to read; see + the MySQL documentation for ``mysql_options()``. + + read_default_group + Default group to read; see the MySQL + documentation for ``mysql_options()``. + + cursorclass + cursor class that ``cursor()`` uses, unless + overridden. Default: ``MySQLdb.cursors.Cursor``. *This + must be a keyword parameter.* + + use_unicode + If True, CHAR and VARCHAR and TEXT columns are returned as + Unicode strings, using the configured character set. It is + best to set the default encoding in the server + configuration, or client configuration (read with + read_default_file). If you change the character set after + connecting (MySQL-4.1 and later), you'll need to put the + correct character set name in connection.charset. + + If False, text-like columns are returned as normal strings, + but you can always write Unicode strings. + + *This must be a keyword parameter.* + + charset + If present, the connection character set will be changed + to this character set, if they are not equal. Support for + changing the character set requires MySQL-4.1 and later + server; if the server is too old, UnsupportedError will be + raised. This option implies use_unicode=True, but you can + override this with use_unicode=False, though you probably + shouldn't. + + If not present, the default character set is used. + + *This must be a keyword parameter.* + + sql_mode + If present, the session SQL mode will be set to the given + string. For more information on sql_mode, see the MySQL + documentation. Only available for 4.1 and newer servers. + + If not present, the session SQL mode will be unchanged. + + *This must be a keyword parameter.* + + ssl + This parameter takes a dictionary or mapping, where the + keys are parameter names used by the mysql_ssl_set_ MySQL + C API call. If this is set, it initiates an SSL connection + to the server; if there is no SSL support in the client, + an exception is raised. *This must be a keyword + parameter.* + +.. _mysql_ssl_set: http://dev.mysql.com/doc/mysql/en/mysql_ssl_set.html + + +apilevel + String constant stating the supported DB API level. '2.0' + +threadsafety + Integer constant stating the level of thread safety the + interface supports. This is set to 1, which means: Threads may + share the module. + + The MySQL protocol can not handle multiple threads using the + same connection at once. Some earlier versions of MySQLdb + utilized locking to achieve a threadsafety of 2. While this is + not terribly hard to accomplish using the standard Cursor class + (which uses ``mysql_store_result()``), it is complicated by + SSCursor (which uses ``mysql_use_result()``; with the latter you + must ensure all the rows have been read before another query can + be executed. It is further complicated by the addition of + transactions, since transactions start when a cursor execute a + query, but end when ``COMMIT`` or ``ROLLBACK`` is executed by + the Connection object. Two threads simply cannot share a + connection while a transaction is in progress, in addition to + not being able to share it during query execution. This + excessively complicated the code to the point where it just + isn't worth it. + + The general upshot of this is: Don't share connections between + threads. It's really not worth your effort or mine, and in the + end, will probably hurt performance, since the MySQL server runs + a separate thread for each connection. You can certainly do + things like cache connections in a pool, and give those + connections to one thread at a time. If you let two threads use + a connection simultaneously, the MySQL client library will + probably upchuck and die. You have been warned. + + For threaded applications, try using a connection pool. + This can be done using the `Pool module`_. + + .. _`Pool module`: http://dustman.net/andy/python/Pool + +charset + The character set used by the connection. In MySQL-4.1 and newer, + it is possible (but not recommended) to change the connection's + character set with an SQL statement. If you do this, you'll also + need to change this attribute. Otherwise, you'll get encoding + errors. + +paramstyle + 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. + + Note that any literal percent signs in the query string passed + to execute() must be escaped, i.e. %%. + + Parameter placeholders can **only** be used to insert column + values. They can **not** be used for other parts of SQL, such as + table names, statements, etc. + +conv + A dictionary or mapping which controls how types are converted + from MySQL to Python and vice versa. + + If the key is a MySQL type (from ``FIELD_TYPE.*``), then the value + can be either: + + * a callable object which takes a string argument (the MySQL + value),' returning a Python value + + * a sequence of 2-tuples, where the first value is a combination + of flags from ``MySQLdb.constants.FLAG``, and the second value + is a function as above. The sequence is tested until the flags + on the field match those of the first value. If both values + are None, then the default conversion is done. Presently this + is only used to distinquish TEXT and BLOB columns. + + If the key is a Python type or class, then the value is a + callable Python object (usually a function) taking two arguments + (value to convert, and the conversion dictionary) which converts + values of this type to a SQL literal string value. + + 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 ``MySQLdb.converters.conversions``. Several + non-standard types are returned as strings, which is how MySQL + returns all columns. For more details, see the built-in module + documentation. + + +Connection Objects +.................. + +Connection objects are returned by the ``connect()`` function. + +commit() + If the database and the tables support transactions, this + commits the current transaction; otherwise this method + successfully does nothing. + +rollback() + If the database and tables support transactions, this rolls back + (cancels) the current transaction; otherwise a + ``NotSupportedError`` is raised. + +cursor([cursorclass]) + MySQL does not support cursors; however, cursors are easily + emulated. You can supply an alternative cursor class as an + optional parameter. If this is not present, it defaults to the + value given when creating the connection object, or the standard + ``Cursor`` class. Also see the additional supplied cursor + classes in the usage section. + +There are many more methods defined on the connection object which +are MySQL-specific. For more information on them, consult the internal +documentation using ``pydoc``. + + +Cursor Objects +.............. + +callproc(procname, args) + Calls stored procedure procname with the sequence of arguments + in args. Returns the original arguments. Stored procedure + support only works with MySQL-5.0 and newer. + + **Compatibility note:** PEP-249_ specifies that if there are + OUT or INOUT parameters, the modified values are to be + returned. This is not consistently possible with MySQL. Stored + procedure arguments must be passed as server variables, and + can only be returned with a SELECT statement. Since a stored + procedure may return zero or more result sets, it is impossible + for MySQLdb to determine if there are result sets to fetch + before the modified parmeters are accessible. + + The parameters are stored in the server as @_*procname*_*n*, + where *n* is the position of the parameter. I.e., if you + cursor.callproc('foo', (a, b, c)), the parameters will be + accessible by a SELECT statement as @_foo_0, @_foo_1, and + @_foo_2. + + **Compatibility note:** It appears that the mere act of + executing the CALL statement produces an empty result set, which + appears after any result sets which might be generated by the + stored procedure. Thus, you will always need to use nextset() to + advance result sets. + +close() + Closes the cursor. Future operations raise ``ProgrammingError``. + If you are using server-side cursors, it is very important to + close the cursor when you are done with it and before creating a + new one. + +info() + Returns some information about the last query. Normally + you don't need to check this. If there are any MySQL + warnings, it will cause a Warning to be issued through + the Python warning module. By default, Warning causes a + message to appear on the console. However, it is possible + to filter these out or cause Warning to be raised as exception. + See the MySQL docs for ``mysql_info()``, and the Python warning + module. (Non-standard) + +setinputsizes() + Does nothing, successfully. + +setoutputsizes() + Does nothing, successfully. + +nextset() + Advances the cursor to the next result set, discarding the remaining + rows in the current result set. If there are no additional result + sets, it returns None; otherwise it returns a true value. + + Note that MySQL doesn't support multiple result sets until 4.1. + + +Some examples +............. + +The ``connect()`` method works nearly the same as with `_mysql`_:: + + import MySQLdb + db=MySQLdb.connect(passwd="moonpie",db="thangs") + +To perform a query, you first need a cursor, and then you can execute +queries on it:: + + c=db.cursor() + max_price=5 + c.execute("""SELECT spam, eggs, sausage FROM breakfast + WHERE price < %s""", (max_price,)) + +In this example, ``max_price=5`` Why, then, use ``%s`` in the +string? Because MySQLdb will convert it to a SQL literal value, which +is the string '5'. When it's finished, the query will actually say, +"...WHERE price < 5". + +Why the tuple? Because the DB API requires you to pass in any +parameters as a sequence. Due to the design of the parser, (max_price) +is interpreted as using algebraic grouping and simply as max_price and +not a tuple. Adding a comma, i.e. (max_price,) forces it to make a +tuple. + +And now, the results:: + + >>> c.fetchone() + (3L, 2L, 0L) + +Quite unlike the ``_mysql`` example, this returns a single tuple, +which is the row, and the values are properly converted by default... +except... What's with the L's? + +As mentioned earlier, while MySQL's INTEGER column translates +perfectly into a Python integer, UNSIGNED INTEGER could overflow, so +these values are converted to Python long integers instead. + +If you wanted more rows, you could use ``c.fetchmany(n)`` or +``c.fetchall()``. These do exactly what you think they do. On +``c.fetchmany(n)``, the ``n`` is optional and defaults to +``c.arraysize``, which is normally 1. Both of these methods return a +sequence of rows, or an empty sequence if there are no more rows. If +you use a weird cursor class, the rows themselves might not be tuples. + +Note that in contrast to the above, ``c.fetchone()`` returns ``None`` +when there are no more rows to fetch. + +The only other method you are very likely to use is when you have to +do a multi-row insert:: + + c.executemany( + """INSERT INTO breakfast (name, spam, eggs, sausage, price) + VALUES (%s, %s, %s, %s, %s)""", + [ + ("Spam and Sausage Lover's Plate", 5, 1, 8, 7.95 ), + ("Not So Much Spam Plate", 3, 2, 0, 3.95 ), + ("Don't Wany ANY SPAM! Plate", 0, 4, 3, 5.95 ) + ] ) + +Here we are inserting three rows of five values. Notice that there is +a mix of types (strings, ints, floats) though we still only use +``%s``. And also note that we only included format strings for one +row. MySQLdb picks those out and duplicates them for each row. + +Using and extending +------------------- + +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 +``connect()`` 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. + +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.cursors: + +BaseCursor + The base class for Cursor objects. This does not raise Warnings. + +CursorStoreResultMixIn + Causes the Cursor to use the ``mysql_store_result()`` function to + get the query result. The entire result set is stored on the + client side. + +CursorUseResultMixIn + Causes the cursor to use the ``mysql_use_result()`` function to + get the query result. The result set is stored on the server side + and is transferred row by row using fetch operations. + +CursorTupleRowsMixIn + Causes the cursor to return rows as a tuple of the column values. + +CursorDictRowsMixIn + + 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, i.e., you are selecting from two + tables that share column names, some of them will be rewritten as + ``table.column``. This can be avoided by using the SQL ``AS`` + keyword. (This is yet-another reason not to use ``*`` in SQL + queries, particularly where ``JOIN`` is involved.) + +Cursor + The default cursor class. This class is composed of + ``CursorWarningMixIn``, ``CursorStoreResultMixIn``, + ``CursorTupleRowsMixIn,`` and ``BaseCursor``, i.e. it raises + ``Warning``, uses ``mysql_store_result()``, and returns rows as + tuples. + +DictCursor + Like ``Cursor`` except it returns rows as dictionaries. + +SSCursor + A "server-side" cursor. Like ``Cursor`` but uses + ``CursorUseResultMixIn``. Use only if you are dealing with + potentially large result sets. + +SSDictCursor + Like ``SSCursor`` except it returns rows as dictionaries. + + +Embedded Server +--------------- + +Instead of connecting to a stand-alone server over the network, +the embedded server support lets you run a full server right in +your Python code or application server. + +If you have built MySQLdb with embedded server support, there +are two additional functions you will need to make use of: + + server_init(args, groups) + Initialize embedded server. If this client is not linked against + the embedded server library, this function does nothing. + + args + sequence of command-line arguments + groups + sequence of groups to use in defaults files + + server_end() + Shut down embedded server. If not using an embedded server, this + does nothing. + +See the MySQL documentation for more information on the embedded +server. + + + +:Title: MySQLdb: a Python interface for MySQL +:Author: Andy Dustman +:Version: $Revision$ -- cgit v1.2.1