Developing Informix Applications in Python

Transcription

1 Developing Informix Applications in Python Carsten Haese Unique Systems, Inc. Informix Forum 2006 Washington, DC December 8-9, 2006

2 Overview Python Features InformixDB Features Installing InformixDB Interactive Tour of InformixDB Real World Example Conclusion 2

3 Python Features Open Source Cross-Platform Easy to learn Dynamic Language Interactive Console Clean Syntax Helpful user community Versatile Small tasks or large applications Stand-alone or embedded Console, GUI, or web applications Rich standard library and 3 rd party extensions Expressive Duck typing, Iterators, HOFs, OOP, Powerful data types, exception handling, memory management Fosters Reusable Code Agile Rapid Application Development Standardized database API 3

4 InformixDB Features DB-API 2.0 compliant Portable (POSIX and Win32 Platforms) Multiple connections Parametrized queries Statement caching and prepared statements Access to sqlcode and sqlerrd Update, delete, and insert cursors Scroll cursors and cursors with hold Supports all IDS data types, including Smart Large Objects, and UDTs 4

5 Installing InformixDB Prerequisites: Python 2.2+ Informix Client SDK Get InformixDB from informixdb.sourceforge.net POSIX Installation: Compile from source python setup.py build_ext python setup.py install (as root) Windows: Installers are provided for Python

6 Establishing a Connection import informixdb conn = informixdb.connect( stores_demo, informix, pw ) 6

7 Static SQL Query cur = conn.cursor() cur.execute( select * from customer ) 7

8 Fetching Data Rows cur.execute( select * from customer ) print cur.fetchone() print cur.fetchmany(5) print cur.fetchall() 8

9 SQL Query with Parameters start_date = raw_input( Start Date: ) end_date = raw_input( End Date: ) Question mark placeholders: cur.execute( select * from orders where order_date between? and?,, (start_date, end_date) ) Numeric placeholders: cur.execute( select * from orders where order_date between :1 and :2,, (start_date, end_date) ) 9

10 SQL Query with Parameters Continued Named placeholders: cur.execute( select * from orders where order_date between :start_date and :end_date,, {'start_date':start_date, 'end_date':end_date} ) Using locals()makes named parameters look like host variables: cur.execute( select * from orders where order_date between :start_date and :end_date,, locals() ) 10

11 Looping through Data Rows Doing it the hard way: cur.execute("select * from orders where customer_num=104") row = cur.fetchone() while row!= None: print "Order %s was placed on %s." % (row[0], row[1]) row = cur.fetchone() Using cursors as iterators is much easier: cur.execute("select * from orders where customer_num=104") for row in cur: print "Order %s was placed on %s." % (row[0], row[1]) 11

12 Column Access Alternatives By default, rows are returned as tuples according to DB-API standard, which requires column access by number. Dictionary cursors return rows as dictionaries that allow column access by name: dictcur = conn.cursor(rowformat=informixdb.row_as_dict) dictcur.execute("select * from orders where customer_num=104") for row in dictcur: print "Order %s was placed on %s.,(row['order_num'], row['order_date']) Object cursors offer a more concise way of accessing columns by name: objcur = conn.cursor(rowformat=informixdb.row_as_object) objcur.execute("select * from orders where customer_num=104") for row in objcur: print "Order %s was placed on %s." % (row.order_num, row.order_date) 12

13 Named Cursor Explicitly named cursors are useful as update or delete cursors: price_increase = {'SMT':4, 'HSK':5, 'SHM':3} updcur = conn.cursor(name="updcur", rowformat=informixdb.row_as_object) updcur.execute("select * from stock for update of unit_price") for row in updcur: increase = price_increase.get(row.manu_code, None) if increase!= None: newprice = row.unit_price * (1.0+increase/100.0) cur.execute("update stock set unit_price=? where current of updcur", [newprice] ) 13

14 Bulk Execution names = [ ( Jonathan, Leffler ), ( Darryl, Priest ), ( Carsten, Haese ) ] cur.executemany( insert into customer(fname,lname) values(?,?),, names ) For insert statements, executemany employs an insert cursor under the hood when possible. 14

15 Prepared Statements get_manu_name = conn.cursor() get_manu_name.prepare( select manu_name from manufact where manu_code=? ) while True: manu_code = raw_input( Enter a manufacturer code: ) if manu_code== : break get_manu_name.execute(none, [manu_code] ) manu_name = get_manu_name.fetchone()[0] print manu_name 15

16 Transactions By default, a connection is always in a transaction. Committing or rolling back the current transaction begins a new transaction. conn.commit() conn.rollback() Sometimes it's useful to work outside of a transaction: conn.autocommit = True 16

17 Scroll Cursor scrollcurs = conn.cursor(scroll=true) scrollcurs.execute( select * from customer order by customer_num ) scrollcurs.scroll(10, absolute ) print scrollcurs.fetchone() scrollcurs.scroll(-5, relative ) print scrollcurs.fetchone() 17

18 Date and Datetime Columns/ Accessing SQLERRD InformixDB uses Python s datetime module for handling date and datetime values. import datetime today = datetime.date.today() cur.execute( insert into orders(customer_num,order_date) values(?,?),, [104,today] ) # Read out sqlerrd to get the serial number of the newly inserted order print cur.sqlerrd 18

19 Error Handling By default, error conditions raise Python exceptions: my_sqlcode = 0 try: cur.execute("sleect * from systables") except informixdb.error, e: my_sqlcode = e.sqlcode print my_sqlcode An errorhandler callback can be set up to customize error handling. 19

20 Describing a Query If a query produces a result set (e.g. SELECT), the cursor s description attribute describes the result columns. If a query doesn t produce a result set, description is None. cur.execute("select * from systables") print cur.description 20

21 Features Not Covered Interval types, date arithmetic, interval arithmetic Working with simple large objects Working with opaque types Using smart large objects as file-like objects 21

22 Real World Example import informixdb from itertools import groupby from operator import attrgetter conn = informixdb.connect("stores_demo") def report_rows(start_date, end_date): main_cur = conn.cursor(rowformat=informixdb.row_as_object) main_cur.execute(""" select customer.*, orders.*, items.* from customer, orders, items where items.order_num = orders.order_num and customer.customer_num = orders.customer_num and orders.order_date between :start_date and :end_date order by customer.customer_num, orders.order_num """, locals() ) for row in main_cur: row.unit_price = row.total_price / row.quantity yield row start_date = raw_input("start Date: ") end_date = raw_input("end Date: ") cust_grouping = groupby(report_rows(start_date, end_date), attrgetter("customer_num", "fname", "lname")) for (cust_code, fname, lname), cust_rows in cust_grouping: cust_total = 0 print "Customer: %s - %s %s" % (cust_code, fname, lname) print ord_grouping = groupby(cust_rows, attrgetter("order_num", "order_date")) for (order_num, order_date), ord_rows in ord_grouping: print " Order: %-10s Order Date: %s" % (order_num, order_date.strftime("%m/%d/%y")) print for row in ord_rows: print " %-10s %5d %7s %7s" % ( row.manu_code+str(row.stock_num), row.quantity, row.unit_price, row.total_price) cust_total += row.total_price print print "Customer Total: %s" % cust_total print "-"*80 print 22

23 Conclusion Thanks to its versatility and agility, Python is an attractive and productive programming language for developing Informix applications - and Python is fun! 23

24 Links Python s Home Page Information on DB Programming in Python Python DB-API specification, version InformixDB on Sourceforge 24

25 Acknowledgments Guido van Rossum and many others for creating Python, Greg Stein, Michael Lorton, Bertil Reinhammar, and Stephen J. Turner, for originally developing and maintaining InformixDB Daniel Smertnig, for contributing improvements to InformixDB 25

26 Developing Informix Applications in Python Carsten Haese Unique Systems, Inc. Informix Forum 2006 Washington, DC December 8-9,