python-apsw-doc 3.7.6.3-r1-1build1 / usr / share / doc / python-apsw / html / _sources / example.txt

.. Automatically generated by example2rst.py.  Edit that file
   not this one!

Example
=======

This code demonstrates usage of the APSW api.  It gives you a good
overview of all the things that can be done.  Also included is output
so you can see what gets printed when you run the code.

.. code-block:: python

    import os, sys, time
    import apsw

    ###
    ### Check we have the expected version of apsw and sqlite
    ###

    print "      Using APSW file",apsw.__file__                # from the extension module
    print "         APSW version",apsw.apswversion()           # from the extension module
    print "   SQLite lib version",apsw.sqlitelibversion()      # from the sqlite library code
    print "SQLite header version",apsw.SQLITE_VERSION_NUMBER   # from the sqlite header file at compile time

.. code-block:: text

   |       Using APSW file /space/apsw/apsw.so
   |          APSW version 3.7.6.3-r1
   |    SQLite lib version 3.7.6.3
   | SQLite header version 3007006

.. code-block:: python

    ###
    ### Opening/creating database
    ###

    connection=apsw.Connection("dbfile")
    cursor=connection.cursor()

.. _example-cursor:

.. code-block:: python

    ###
    ### simple statement
    ###

    cursor.execute("create table foo(x,y,z)")

    ###
    ### using different types
    ###

    cursor.execute("insert into foo values(?,?,?)", (1, 1.1, None))  # integer, float/real, Null
    cursor.execute("insert into foo(x) values(?)", ("abc", ))        # string (note trailing comma to ensure tuple!)
    cursor.execute("insert into foo(x) values(?)",                   # a blob (binary data)
                        (buffer("abc\xff\xfe"), ))                   # Use b"abc\xff\xfe" for Python 3

    ###
    ### multiple statements
    ###

    cursor.execute("delete from foo; insert into foo values(1,2,3); create table bar(a,b,c) ; insert into foo values(4, 'five', 6.0)")

    ###
    ### iterator
    ###

    for x,y,z in cursor.execute("select x,y,z from foo"):
        print cursor.getdescription()  # shows column names and declared types
        print x,y,z

    ###
    ### iterator - multiple statements
    ###

    for m,n,o in cursor.execute("select x,y,z from foo ; select a,b,c from bar"):
        print m,n,o

    ###
    ### bindings - sequence
    ###

    cursor.execute("insert into foo values(?,?,?)", (7, 'eight', False))
    cursor.execute("insert into foo values(?,?,?1)", ('one', 'two'))  # nb sqlite does the numbers from 1

    ###
    ### bindings - dictionary
    ###

    cursor.execute("insert into foo values(:alpha, :beta, :gamma)", {'alpha': 1, 'beta': 2, 'gamma': 'three'})

.. _example-exectrace:

.. code-block:: python

    ###
    ### tracing execution
    ###

    def mytrace(cursor, statement, bindings):
        "Called just before executing each statement"
        print "SQL:",statement
        if bindings:
            print "Bindings:",bindings
        return True  # if you return False then execution is aborted

    cursor.setexectrace(mytrace)
    cursor.execute("drop table bar ; create table bar(x,y,z); select * from foo where x=?", (3,))

.. code-block:: text

   | SQL: drop table bar ;
   | SQL: create table bar(x,y,z);
   | SQL: select * from foo where x=?
   | Bindings: (3,)

.. _example-rowtrace:

.. code-block:: python

    ###
    ### tracing results
    ###

    def rowtrace(cursor, row):
        """Called with each row of results before they are handed off.  You can return None to
        cause the row to be skipped or a different set of values to return"""
        print "Row:", row
        return row

    cursor.setrowtrace(rowtrace)
    for row in cursor.execute("select x,y from foo where x>3"):
         pass

.. code-block:: text

   | SQL: select x,y from foo where x>3
   | Row: (4, 'five')
   | Row: (7, 'eight')
   | Row: ('one', 'two')

.. code-block:: python

    # Clear tracers
    cursor.setrowtrace(None)
    cursor.setexectrace(None)

    ###
    ### executemany
    ###

    # (This will work correctly with multiple statements, as well as statements that
    # return data.  The second argument can be anything that is iterable.)
    cursor.executemany("insert into foo (x) values(?)", ( [1], [2], [3] ) )

    # You can also use it for statements that return data
    for row in cursor.executemany("select * from foo where x=?", ( [1], [2], [3] ) ):
        print row

.. _scalar-example:

.. code-block:: python

    ###
    ### defining your own functions
    ###

    def ilove7(*args):
        "a scalar function"
        print "ilove7 got",args,"but I love 7"
        return 7

    connection.createscalarfunction("seven", ilove7)

    for row in cursor.execute("select seven(x,y) from foo"):
        print row

.. code-block:: text

   | ilove7 got (1, 2) but I love 7
   | (7,)
   | ilove7 got (4, 'five') but I love 7
   | (7,)
   | ilove7 got (7, 'eight') but I love 7
   | (7,)
   | ilove7 got ('one', 'two') but I love 7
   | (7,)
   | ilove7 got (1, 2) but I love 7
   | (7,)
   | ilove7 got (1, None) but I love 7
   | (7,)
   | ilove7 got (2, None) but I love 7
   | (7,)
   | ilove7 got (3, None) but I love 7
   | (7,)

.. _aggregate-example:

.. code-block:: python

    ###
    ### aggregate functions are more complex
    ###

    # Here we return the longest item when represented as a string.

    class longest:
        def __init__(self):
            self.longest=""

        def step(self, *args):
            for arg in args:
                if len( str(arg) ) > len (self.longest):
                    self.longest=str(arg)

        def final(self):
            return self.longest

        # Under Python 2.3 remove the following line and add
        # factory=classmethod(factory) at the end
        @classmethod
        def factory(cls):
            return cls(), cls.step, cls.final

    connection.createaggregatefunction("longest", longest.factory)
    for row in cursor.execute("select longest(x,y) from foo"):
        print row

.. code-block:: text

   | ('eight',)

.. _collation-example:

.. code-block:: python

    ###
    ### Defining collations.
    ###

    # The default sorting mechanisms don't understand numbers at the end of strings
    # so here we define a collation that does

    cursor.execute("create table s(str)")
    cursor.executemany("insert into s values(?)",
                      ( ["file1"], ["file7"], ["file17"], ["file20"], ["file3"] ) )

    for row in cursor.execute("select * from s order by str"):
        print row

.. code-block:: text

   | ('file1',)
   | ('file17',)
   | ('file20',)
   | ('file3',)
   | ('file7',)

.. code-block:: python

    def strnumcollate(s1, s2):
        # return -1 if s1<s2, +1 if s1>s2 else 0

        # split values into two parts - the head and the numeric tail
        values=[s1, s2]
        for vn,v in enumerate(values):
            for i in range(len(v), 0, -1):
                if v[i-1] not in "01234567890":
                    break
            try:
                v=( v[:i], int(v[i:]) )
            except ValueError:
                v=( v[:i], None )
            values[vn]=v
        # compare
        if values[0]<values[1]:
            return -1
        if values[0]>values[1]:
            return 1
        return 0

    connection.createcollation("strnum", strnumcollate)

    for row in cursor.execute("select * from s order by str collate strnum"):
        print row

.. code-block:: text

   | ('file1',)
   | ('file3',)
   | ('file7',)
   | ('file17',)
   | ('file20',)

.. _authorizer-example:

.. code-block:: python

    ###
    ### Authorizer (eg if you want to control what user supplied SQL can do)
    ###

    def authorizer(operation, paramone, paramtwo, databasename, triggerorview):
        """Called when each operation is prepared.  We can return SQLITE_OK, SQLITE_DENY or
        SQLITE_IGNORE"""
        # find the operation name
        print apsw.mapping_authorizer_function[operation],
        print paramone, paramtwo, databasename, triggerorview
        if operation==apsw.SQLITE_CREATE_TABLE and paramone.startswith("private"):
            return apsw.SQLITE_DENY  # not allowed to create tables whose names start with private

        return apsw.SQLITE_OK  # always allow

    connection.setauthorizer(authorizer)
    cursor.execute("insert into s values('foo')")
    cursor.execute("select str from s limit 1")

.. code-block:: text

   | SQLITE_INSERT s None main None
   | SQLITE_SELECT None None None None
   | SQLITE_READ s str main None

.. code-block:: python

    # Cancel authorizer
    connection.setauthorizer(None)

.. _example-progress-handler:

.. code-block:: python

    ###
    ### progress handler (SQLite 3 experimental feature)
    ###

    # something to give us large numbers of random numbers
    import random
    def randomintegers(howmany):
        for i in xrange(howmany):
            yield (random.randint(0,9999999999),)

    # create a table with 100 random numbers
    cursor.execute("begin ; create table bigone(x)")
    cursor.executemany("insert into bigone values(?)", randomintegers(100))
    cursor.execute("commit")

    # display an ascii spinner
    _phcount=0
    _phspinner="|/-\\"
    def progresshandler():
        global _phcount
        sys.stdout.write(_phspinner[_phcount%len(_phspinner)]+chr(8)) # chr(8) is backspace
        sys.stdout.flush()
        _phcount+=1
        time.sleep(0.1) # deliberate delay so we can see the spinner (SQLite is too fast otherwise!)
        return 0  # returning non-zero aborts

    # register progresshandler every 20 instructions
    connection.setprogresshandler(progresshandler, 20)

    # see it in action - sorting 100 numbers to find the biggest takes a while
    print "spinny thing -> ",
    for i in cursor.execute("select max(x) from bigone"):
        print # newline
        print i # and the maximum number

    connection.setprogresshandler(None)

.. _example-commithook:

.. code-block:: python

    ###
    ### commit hook (SQLite3 experimental feature)
    ###

    def mycommithook():
        print "in commit hook"
        hour=time.localtime()[3]
        if hour<8 or hour>17:
            print "no commits out of hours"
            return 1  # abort commits outside of 8am through 6pm
        print "commits okay at this time"
        return 0  # let commit go ahead

    connection.setcommithook(mycommithook)
    try:
        cursor.execute("begin; create table example(x,y,z); insert into example values (3,4,5) ; commit")
    except apsw.ConstraintError:
        print "commit was not allowed"

    connection.setcommithook(None)

.. code-block:: text

   | in commit hook
   | no commits out of hours
   | commit was not allowed

.. _example-updatehook:

.. code-block:: python

    ###
    ### update hook
    ###

    def myupdatehook(type, databasename, tablename, rowid):
        print "Updated: %s database %s, table %s, row %d" % (
            apsw.mapping_authorizer_function[type], databasename, tablename, rowid)

    connection.setupdatehook(myupdatehook)
    cursor.execute("insert into s values(?)", ("file93",))
    cursor.execute("update s set str=? where str=?", ("file94", "file93"))
    cursor.execute("delete from s where str=?", ("file94",))
    connection.setupdatehook(None)

.. code-block:: text

   | Updated: SQLITE_INSERT database main, table s, row 7
   | Updated: SQLITE_UPDATE database main, table s, row 7
   | Updated: SQLITE_DELETE database main, table s, row 7

.. _example-blobio:

.. code-block:: python

    ###
    ### Blob I/O
    ###

    cursor.execute("create table blobby(x,y)")
    # Add a blob we will fill in later
    cursor.execute("insert into blobby values(1,zeroblob(10000))")
    # Or as a binding
    cursor.execute("insert into blobby values(2,?)", (apsw.zeroblob(20000),))
    # Open a blob for writing.  We need to know the rowid
    rowid=cursor.execute("select ROWID from blobby where x=1").next()[0]
    blob=connection.blobopen("main", "blobby", "y", rowid, 1) # 1 is for read/write
    blob.write("hello world")
    blob.seek(2000)
    blob.write("hello world, again")
    blob.close()

.. _example-vtable:

.. code-block:: python

    ###
    ### Virtual tables
    ###

    # This virtual table stores information about files in a set of
    # directories so you can execute SQL queries

    def getfiledata(directories):
        columns=None
        data=[]
        counter=1
        for directory in directories:
            for f in os.listdir(directory):
                if not os.path.isfile(os.path.join(directory,f)):
                    continue
                counter+=1
                st=os.stat(os.path.join(directory,f))
                if columns is None:
                    columns=["rowid", "name", "directory"]+[x for x in dir(st) if x.startswith("st_")]
                data.append( [counter, f, directory] + [getattr(st,x) for x in columns[3:]] )
        return columns, data

    # This gets registered with the Connection
    class Source:
        def Create(self, db, modulename, dbname, tablename, *args):
            columns,data=getfiledata([eval(a.replace("\\", "\\\\")) for a in args]) # eval strips off layer of quotes
            schema="create table foo("+','.join(["'%s'" % (x,) for x in columns[1:]])+")"
            return schema,Table(columns,data)
        Connect=Create

    # Represents a table
    class Table:
        def __init__(self, columns, data):
            self.columns=columns
            self.data=data

        def BestIndex(self, *args):
            return None

        def Open(self):
            return Cursor(self)

        def Disconnect(self):
            pass

        Destroy=Disconnect

    # Represents a cursor
    class Cursor:
        def __init__(self, table):
            self.table=table

        def Filter(self, *args):
            self.pos=0

        def Eof(self):
            return self.pos>=len(self.table.data)

        def Rowid(self):
            return self.table.data[self.pos][0]

        def Column(self, col):
            return self.table.data[self.pos][1+col]

        def Next(self):
            self.pos+=1

        def Close(self):
            pass

    # Register the module as filesource
    connection.createmodule("filesource", Source())

    # Arguments to module - all directories in sys.path
    sysdirs=",".join(["'%s'" % (x,) for x in sys.path[1:] if len(x) and os.path.isdir(x)])
    cursor.execute("create virtual table sysfiles using filesource("+sysdirs+")")

    # Which 3 files are the biggest?
    for size,directory,file in cursor.execute("select st_size,directory,name from sysfiles order by st_size desc limit 3"):
        print size,file,directory

.. code-block:: text

   | 9510280 qt.so /usr/lib/pymodules/python2.7
   | 3226728 apsw.o /space/apsw
   | 3133370 apsw.so /space/apsw

.. code-block:: python

    # Which 3 files are the oldest?
    for ctime,directory,file in cursor.execute("select st_ctime,directory,name from sysfiles order by st_ctime limit 3"):
        print ctime,file,directory

.. code-block:: text

   | 1288928270.12 LICENSE /space/apsw
   | 1288928270.6 setup.cfg /space/apsw
   | 1289174179.62 pexpect-2.3.egg-info /usr/lib/python2.7/dist-packages

.. _example-vfs:

.. code-block:: python

    ###
    ### A VFS that "obfuscates" the database file contents.  The scheme
    ### used is to xor all bytes with 0xa5.  This scheme honours that used
    ### for MAPI and SQL Server.
    ###

    def encryptme(data):
        if not data: return data
        return "".join([chr(ord(x)^0xa5) for x in data])

    # Inheriting from a base of "" means the default vfs
    class ObfuscatedVFS(apsw.VFS):
        def __init__(self, vfsname="obfu", basevfs=""):
            self.vfsname=vfsname
            self.basevfs=basevfs
            apsw.VFS.__init__(self, self.vfsname, self.basevfs)

        # We want to return our own file implmentation, but also
        # want it to inherit
        def xOpen(self, name, flags):
            return ObfuscatedVFSFile(self.basevfs, name, flags)

    # The file implementation where we override xRead and xWrite to call our
    # encryption routine
    class ObfuscatedVFSFile(apsw.VFSFile):
        def __init__(self, inheritfromvfsname, filename, flags):
            apsw.VFSFile.__init__(self, inheritfromvfsname, filename, flags)

        def xRead(self, amount, offset):
            return encryptme(super(ObfuscatedVFSFile, self).xRead(amount, offset))

        def xWrite(self, data, offset):
            super(ObfuscatedVFSFile, self).xWrite(encryptme(data), offset)

    # To register the VFS we just instantiate it
    obfuvfs=ObfuscatedVFS()
    # Lets see what vfs are now available?
    print apsw.vfsnames()

.. code-block:: text

   | ['unix', 'obfu', 'unix-excl', 'unix-dotfile', 'unix-none']

.. code-block:: python

    # Make an obfuscated db
    obfudb=apsw.Connection("myobfudb", vfs=obfuvfs.vfsname)
    # Check it works
    obfudb.cursor().execute("create table foo(x,y); insert into foo values(1,2)")

    # Check it really is obfuscated on disk
    print `open("myobfudb", "rb").read()[:20]`

.. code-block:: text

   | '\xf6\xf4\xe9\xcc\xd1\xc0\x85\xc3\xca\xd7\xc8\xc4\xd1\x85\x96\xa5\xa1\xa5\xa4\xa4'

.. code-block:: python

    # And unobfuscating it
    print `encryptme(open("myobfudb", "rb").read()[:20])`

.. code-block:: text

   | 'SQLite format 3\x00\x04\x00\x01\x01'

.. code-block:: python

    # Tidy up
    obfudb.close()
    os.remove("myobfudb")

.. _example-limit:

.. code-block:: python

    ###
    ### Limits
    ###

    # Print some limits
    for limit in ("LENGTH", "COLUMN", "ATTACHED"):
        name="SQLITE_LIMIT_"+limit
        maxname="SQLITE_MAX_"+limit  # compile time
        orig=connection.limit(getattr(apsw, name))
        print name, orig
        # To get the maximum, set to 0x7fffffff and then read value back
        connection.limit(getattr(apsw, name), 0x7fffffff)
        max=connection.limit(getattr(apsw, name))
        print maxname, max

    # Set limit for size of a string
    cursor.execute("create table testlimit(s)")
    cursor.execute("insert into testlimit values(?)", ( "x"*1024, )) # 1024 char string
    connection.limit(apsw.SQLITE_LIMIT_LENGTH, 1023) # limit is now 1023
    try:
        cursor.execute("insert into testlimit values(?)", ( "y"*1024, ))
        print "string exceeding limit was inserted"
    except apsw.TooBigError:
        print "Caught toobig exception"
    connection.limit(apsw.SQLITE_LIMIT_LENGTH, 0x7fffffff)

.. code-block:: text

   | SQLITE_LIMIT_LENGTH 1000000000
   | SQLITE_MAX_LENGTH 1000000000
   | SQLITE_LIMIT_COLUMN 2000
   | SQLITE_MAX_COLUMN 2000
   | SQLITE_LIMIT_ATTACHED 10
   | SQLITE_MAX_ATTACHED 10
   | Caught toobig exception

.. _example-backup:

.. code-block:: python

    ###
    ### Backup to memory
    ###

    # We will copy the disk database into a memory database

    memcon=apsw.Connection(":memory:")

    # Copy into memory
    with memcon.backup("main", connection, "main") as backup:
        backup.step() # copy whole database in one go

    # There will be no disk accesses for this query
    for row in memcon.cursor().execute("select * from s"):
        pass

.. _example-shell:

.. code-block:: python

    ###
    ### Shell
    ###

    # Here we use the shell to do a csv export providing the existing db
    # connection

    # Export to a StringIO
    import StringIO as io # use io in Python 3
    output=io.StringIO()
    shell=apsw.Shell(stdout=output, db=connection)
    # How to execute a dot command
    shell.process_command(".mode csv")
    # How to execute SQL
    shell.process_sql("create table csvtest(x,y); insert into csvtest values(3,4); insert into csvtest values('ab', NULL)")
    # Let the shell figure out SQL vs dot command
    shell.process_complete_line("select * from csvtest")

    # Verify output
    print output.getvalue()

.. code-block:: text

   | 3,4
   | ab,
   | 

.. _example-status:

.. code-block:: python

    ###
    ### Statistics
    ###

    print "SQLite memory usage current %d max %d" % apsw.status(apsw.SQLITE_STATUS_MEMORY_USED)

.. code-block:: text

   | SQLite memory usage current 313784 max 318624

.. code-block:: python

    ###
    ### Cleanup
    ###

    # We can close connections manually (useful if you want to catch exceptions)
    # but you don't have to
    connection.close(True)  # force it since we want to exit

    # Delete database - we don't need it any more
    os.remove("dbfile")