\section{\module{sqlite3} ---         DB-API 2.0 interface for SQLite databases} \declaremodule{builtin}{sqlite3}\modulesynopsis{A DB-API 2.0 implementation using SQLite 3.x.}\sectionauthor{Gerhard Häring}{gh@ghaering.de}\versionadded{2.5} SQLite is a C library that provides a lightweight disk-based databasethat doesn't require a separate server process and allows accessingthe database using a nonstandard variant of the SQL query language.Some applications can use SQLite for internal data storage.  It's alsopossible to prototype an application using SQLite and then port thecode to a larger database such as PostgreSQL or Oracle. pysqlite was written by Gerhard H\"aring and provides a SQL interfacecompliant with the DB-API 2.0 specification described by\pep{249}.  To use the module, you must first create a \class{Connection} objectthat represents the database.  Here the data will be stored in the \file{/tmp/example} file: \begin{verbatim}conn = sqlite3.connect('/tmp/example')\end{verbatim} You can also supply the special name \samp{:memory:} to createa database in RAM. Once you have a \class{Connection}, you can create a \class{Cursor} object and call its \method{execute()} method to perform SQL commands: \begin{verbatim}c = conn.cursor() # Create tablec.execute('''create table stocks(date text, trans text, symbol text, qty real, price real)''') # Insert a row of datac.execute("""insert into stocks          values ('2006-01-05','BUY','RHAT',100,35.14)""")\end{verbatim}     Usually your SQL operations will need to use values from Pythonvariables.  You shouldn't assemble your query using Python's stringoperations because doing so is insecure; it makes your programvulnerable to an SQL injection attack.   Instead, use the DB-API's parameter substitution.  Put \samp{?} as aplaceholder wherever you want to use a value, and then provide a tupleof values as the second argument to the cursor's \method{execute()}method.  (Other database modules may use a different placeholder,such as \samp{\%s} or \samp{:1}.) For example: \begin{verbatim}    # Never do this -- insecure!symbol = 'IBM'c.execute("... where symbol = '%s'" % symbol) # Do this insteadt = (symbol,)c.execute('select * from stocks where symbol=?', t) # Larger examplefor t in (('2006-03-28', 'BUY', 'IBM', 1000, 45.00),          ('2006-04-05', 'BUY', 'MSOFT', 1000, 72.00),          ('2006-04-06', 'SELL', 'IBM', 500, 53.00),         ):    c.execute('insert into stocks values (?,?,?,?,?)', t)\end{verbatim} To retrieve data after executing a SELECT statement, you can either treat the cursor as an iterator, call the cursor's \method{fetchone()}method to retrieve a single matching row, or call \method{fetchall()} to get a list of the matching rows. This example uses the iterator form: \begin{verbatim}>>> c = conn.cursor()>>> c.execute('select * from stocks order by price')>>> for row in c:...    print row...(u'2006-01-05', u'BUY', u'RHAT', 100, 35.140000000000001)(u'2006-03-28', u'BUY', u'IBM', 1000, 45.0)(u'2006-04-06', u'SELL', u'IBM', 500, 53.0)(u'2006-04-05', u'BUY', u'MSOFT', 1000, 72.0)>>>\end{verbatim} \begin{seealso} \seeurl{http://www.pysqlite.org}{The pysqlite web page.} \seeurl{http://www.sqlite.org}{The SQLite web page; the documentation describes the syntax and theavailable data types for the supported SQL dialect.} \seepep{249}{Database API Specification 2.0}{PEP written byMarc-Andr\'e Lemburg.} \end{seealso}  \subsection{Module functions and constants\label{sqlite3-Module-Contents}} \begin{datadesc}{PARSE_DECLTYPES}This constant is meant to be used with the \var{detect_types} parameter of the\function{connect} function. Setting it makes the \module{sqlite3} module parse the declared type for each column itreturns.  It will parse out the first word of the declared type, i. e. for"integer primary key", it will parse out "integer". Then for that column, itwill look into the converters dictionary and use the converter functionregistered for that type there.  Converter names are case-sensitive!\end{datadesc}  \begin{datadesc}{PARSE_COLNAMES}This constant is meant to be used with the \var{detect_types} parameter of the\function{connect} function. Setting this makes the SQLite interface parse the column name for each columnit returns.  It will look for a string formed [mytype] in there, and thendecide that 'mytype' is the type of the column. It will try to find an entry of'mytype' in the converters dictionary and then use the converter function foundthere to return the value. The column name found in \member{cursor.description} is onlythe first word of the column name, i.  e. if you use something like\code{'as "x [datetime]"'} in your SQL, then we will parse out everything until thefirst blank for the column name: the column name would simply be "x".\end{datadesc} \begin{funcdesc}{connect}{database\optional{, timeout, isolation_level, detect_types, factory}}Opens a connection to the SQLite database file \var{database}. You can use\code{":memory:"} to open a database connection to a database that resides inRAM instead of on disk. When a database is accessed by multiple connections, and one of the processesmodifies the database, the SQLite database is locked until that transaction iscommitted. The \var{timeout} parameter specifies how long the connection shouldwait for the lock to go away until raising an exception. The default for thetimeout parameter is 5.0 (five seconds).  For the \var{isolation_level} parameter, please see the \member{isolation_level}property of \class{Connection} objects in section~\ref{sqlite3-Connection-IsolationLevel}. SQLite natively supports only the types TEXT, INTEGER, FLOAT, BLOB and NULL. Ifyou want to use other types, like you have to add support for them yourself.The \var{detect_types} parameter and the using custom \strong{converters} registered withthe module-level \function{register_converter} function allow you to easily do that. \var{detect_types} defaults to 0 (i. e. off, no type detection), you can set itto any combination of \constant{PARSE_DECLTYPES} and \constant{PARSE_COLNAMES} to turn typedetection on. By default, the \module{sqlite3} module uses its \class{Connection} class for theconnect call.  You can, however, subclass the \class{Connection} class and make\function{connect} use your class instead by providing your class for the\var{factory} parameter. Consult the section \ref{sqlite3-Types} of this manual for details. The \module{sqlite3} module internally uses a statement cache to avoid SQL parsingoverhead. If you want to explicitly set the number of statements that arecached for the connection, you can set the \var{cached_statements} parameter.The currently implemented default is to cache 100 statements.\end{funcdesc} \begin{funcdesc}{register_converter}{typename, callable}Registers a callable to convert a bytestring from the database into a customPython type. The callable will be invoked for all database values that are ofthe type \var{typename}. Confer the parameter \var{detect_types} of the\function{connect} function for how the type detection works. Note that the case of\var{typename} and the name of the type in your query must match!\end{funcdesc} \begin{funcdesc}{register_adapter}{type, callable}Registers a callable to convert the custom Python type \var{type} into one ofSQLite's supported types. The callable \var{callable} accepts as singleparameter the Python value, and must return a value of the following types:int, long, float, str (UTF-8 encoded), unicode or buffer.\end{funcdesc} \begin{funcdesc}{complete_statement}{sql}Returns \constant{True} if the string \var{sql} contains one or more complete SQLstatements terminated by semicolons. It does not verify that the SQL issyntactically correct, only that there are no unclosed string literals and thestatement is terminated by a semicolon. This can be used to build a shell for SQLite, as in the following example:     \verbatiminput{sqlite3/complete_statement.py}\end{funcdesc} \begin{funcdesc}{enable_callback_tracebacks}{flag}By default you will not get any tracebacks in user-defined functions,aggregates, converters, authorizer callbacks etc. If you want to debug them,you can call this function with \var{flag} as True. Afterwards, you will gettracebacks from callbacks on \code{sys.stderr}. Use \constant{False} to disablethe feature again.\end{funcdesc} \subsection{Connection Objects \label{sqlite3-Connection-Objects}} A \class{Connection} instance has the following attributes and methods: \label{sqlite3-Connection-IsolationLevel}\begin{memberdesc}{isolation_level}  Get or set the current isolation level. None for autocommit mode or one of  "DEFERRED", "IMMEDIATE" or "EXLUSIVE". See ``Controlling Transactions'',   section~\ref{sqlite3-Controlling-Transactions}, for a more detailed explanation.\end{memberdesc} \begin{methoddesc}{cursor}{\optional{cursorClass}}  The cursor method accepts a single optional parameter \var{cursorClass}.  If supplied, this must be a custom cursor class that extends   \class{sqlite3.Cursor}.\end{methoddesc} \begin{methoddesc}{execute}{sql, \optional{parameters}}This is a nonstandard shortcut that creates an intermediate cursor object bycalling the cursor method, then calls the cursor's \method{execute} method with theparameters given.\end{methoddesc} \begin{methoddesc}{executemany}{sql, \optional{parameters}}This is a nonstandard shortcut that creates an intermediate cursor object bycalling the cursor method, then calls the cursor's \method{executemany} method with theparameters given.\end{methoddesc} \begin{methoddesc}{executescript}{sql_script}This is a nonstandard shortcut that creates an intermediate cursor object bycalling the cursor method, then calls the cursor's \method{executescript} method with theparameters given.\end{methoddesc} \begin{methoddesc}{create_function}{name, num_params, func} Creates a user-defined function that you can later use from within SQLstatements under the function name \var{name}. \var{num_params} is the numberof parameters the function accepts, and \var{func} is a Python callable that iscalled as the SQL function. The function can return any of the types supported by SQLite: unicode, str,int, long, float, buffer and None. Example:   \verbatiminput{sqlite3/md5func.py}\end{methoddesc} \begin{methoddesc}{create_aggregate}{name, num_params, aggregate_class} Creates a user-defined aggregate function. The aggregate class must implement a \code{step} method, which accepts thenumber of parameters \var{num_params}, and a \code{finalize} method whichwill return the final result of the aggregate. The \code{finalize} method can return any of the types supported by SQLite:unicode, str, int, long, float, buffer and None. Example:   \verbatiminput{sqlite3/mysumaggr.py}\end{methoddesc} \begin{methoddesc}{create_collation}{name, callable} Creates a collation with the specified \var{name} and \var{callable}. Thecallable will be passed two string arguments. It should return -1 if the firstis ordered lower than the second, 0 if they are ordered equal and 1 if thefirst is ordered higher than the second.  Note that this controls sorting(ORDER BY in SQL) so your comparisons don't affect other SQL operations. Note that the callable will get its parameters as Python bytestrings, whichwill normally be encoded in UTF-8. The following example shows a custom collation that sorts "the wrong way":   \verbatiminput{sqlite3/collation_reverse.py} To remove a collation, call \code{create_collation} with None as callable: \begin{verbatim}    con.create_collation("reverse", None)\end{verbatim}\end{methoddesc} \begin{methoddesc}{interrupt}{} You can call this method from a different thread to abort any queries thatmight be executing on the connection. The query will then abort and the callerwill get an exception.\end{methoddesc} \begin{methoddesc}{set_authorizer}{authorizer_callback} This routine registers a callback. The callback is invoked for each attempt toaccess a column of a table in the database. The callback should return\constant{SQLITE_OK} if access is allowed, \constant{SQLITE_DENY} if the entireSQL statement should be aborted with an error and \constant{SQLITE_IGNORE} ifthe column should be treated as a NULL value. These constants are available inthe \module{sqlite3} module. The first argument to the callback signifies what kind of operation is to beauthorized. The second and third argument will be arguments or \constant{None}depending on the first argument. The 4th argument is the name of the database("main", "temp", etc.) if applicable. The 5th argument is the name of theinner-most trigger or view that is responsible for the access attempt or\constant{None} if this access attempt is directly from input SQL code. Please consult the SQLite documentation about the possible values for the firstargument and the meaning of the second and third argument depending on thefirst one. All necessary constants are available in the \module{sqlite3}module.\end{methoddesc} \begin{memberdesc}{row_factory}  You can change this attribute to a callable that accepts the cursor and  the original row as a tuple and will return the real result row.  This  way, you can implement more advanced ways of returning results, such   as returning an object that can also access columns by name.   Example:   \verbatiminput{sqlite3/row_factory.py}   If returning a tuple doesn't suffice and you want name-based  access to columns, you should consider setting \member{row_factory} to the  highly-optimized \class{sqlite3.Row} type. \class{Row} provides both  index-based and case-insensitive name-based access to columns with almost  no memory overhead. It will probably be better than your own custom   dictionary-based approach or even a db_row based solution.  % XXX what's a db_row-based solution?\end{memberdesc} \begin{memberdesc}{text_factory}  Using this attribute you can control what objects are returned for the  TEXT data type. By default, this attribute is set to \class{unicode} and  the \module{sqlite3} module will return Unicode objects for TEXT. If you want to return  bytestrings instead, you can set it to \class{str}.   For efficiency reasons, there's also a way to return Unicode objects only  for non-ASCII data, and bytestrings otherwise. To activate it, set this  attribute to \constant{sqlite3.OptimizedUnicode}.   You can also set it to any other callable that accepts a single bytestring  parameter and returns the resulting object.   See the following example code for illustration:   \verbatiminput{sqlite3/text_factory.py}\end{memberdesc} \begin{memberdesc}{total_changes}  Returns the total number of database rows that have been modified, inserted,  or deleted since the database connection was opened.\end{memberdesc}     \subsection{Cursor Objects \label{sqlite3-Cursor-Objects}} A \class{Cursor} instance has the following attributes and methods: \begin{methoddesc}{execute}{sql, \optional{parameters}} Executes a SQL statement. The SQL statement may be parametrized (i. e.placeholders instead of SQL literals). The \module{sqlite3} module supports two kinds ofplaceholders: question marks (qmark style) and named placeholders (namedstyle). This example shows how to use parameters with qmark style:     \verbatiminput{sqlite3/execute_1.py} This example shows how to use the named style:     \verbatiminput{sqlite3/execute_2.py}     \method{execute()} will only execute a single SQL statement. If you try to    execute more than one statement with it, it will raise a Warning. Use    \method{executescript()} if you want to execute multiple SQL statements with one    call.\end{methoddesc}  \begin{methoddesc}{executemany}{sql, seq_of_parameters}Executes a SQL command against all parameter sequences or mappings found in thesequence \var{sql}. The \module{sqlite3} module also allowsusing an iterator yielding parameters instead of a sequence. \verbatiminput{sqlite3/executemany_1.py} Here's a shorter example using a generator: \verbatiminput{sqlite3/executemany_2.py}\end{methoddesc} \begin{methoddesc}{executescript}{sql_script} This is a nonstandard convenience method for executing multiple SQL statementsat once. It issues a COMMIT statement first, then executes the SQL script itgets as a parameter. \var{sql_script} can be a bytestring or a Unicode string. Example: \verbatiminput{sqlite3/executescript.py}\end{methoddesc} \begin{memberdesc}{rowcount}  Although the \class{Cursor} class of the \module{sqlite3} module implements this  attribute, the database engine's own support for the determination of "rows  affected"/"rows selected" is quirky.   For \code{SELECT} statements, \member{rowcount} is always None because we cannot  determine the number of rows a query produced until all rows were fetched.   For \code{DELETE} statements, SQLite reports \member{rowcount} as 0 if you make a  \code{DELETE FROM table} without any condition.   For \method{executemany} statements, the number of modifications are summed  up into \member{rowcount}.   As required by the Python DB API Spec, the \member{rowcount} attribute "is -1  in case no executeXX() has been performed on the cursor or the rowcount  of the last operation is not determinable by the interface".\end{memberdesc} \subsection{SQLite and Python types\label{sqlite3-Types}} \subsubsection{Introduction} SQLite natively supports the following types: NULL, INTEGER, REAL, TEXT, BLOB. The following Python types can thus be sent to SQLite without any problem: \begin{tableii}  {c|l}{code}{Python type}{SQLite type}\lineii{None}{NULL}\lineii{int}{INTEGER}\lineii{long}{INTEGER}\lineii{float}{REAL}\lineii{str (UTF8-encoded)}{TEXT}\lineii{unicode}{TEXT}\lineii{buffer}{BLOB}\end{tableii} This is how SQLite types are converted to Python types by default: \begin{tableii}  {c|l}{code}{SQLite type}{Python type}\lineii{NULL}{None}\lineii{INTEGER}{int or long, depending on size}\lineii{REAL}{float}\lineii{TEXT}{depends on text_factory, unicode by default}\lineii{BLOB}{buffer}\end{tableii} The type system of the \module{sqlite3} module is extensible in two ways: you can storeadditional Python types in a SQLite database via object adaptation, and you canlet the \module{sqlite3} module convert SQLite types to different Python types viaconverters. \subsubsection{Using adapters to store additional Python types in SQLite databases} As described before, SQLite supports only a limited set of types natively. Touse other Python types with SQLite, you must \strong{adapt} them to one of the sqlite3module's supported types for SQLite: one of NoneType, int, long, float,str, unicode, buffer. The \module{sqlite3} module uses Python object adaptation, as described in \pep{246} for this.  The protocol to use is \class{PrepareProtocol}. There are two ways to enable the \module{sqlite3} module to adapt a custom Python typeto one of the supported ones. \paragraph{Letting your object adapt itself} This is a good approach if you write the class yourself. Let's suppose you havea class like this: \begin{verbatim}class Point(object):    def __init__(self, x, y):        self.x, self.y = x, y\end{verbatim} Now you want to store the point in a single SQLite column.  First you'll have tochoose one of the supported types first to be used for representing the point.Let's just use str and separate the coordinates using a semicolon. Then youneed to give your class a method \code{__conform__(self, protocol)} which must

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