basic.py :  » Database » PyPgSQL » pyPgSQL-2.5.1 » examples » Python Open Source

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Python Open Source » Database » PyPgSQL 
PyPgSQL » pyPgSQL 2.5.1 » examples » basic.py
#!/usr/local/bin/python
import sys, os, string
from pyPgSQL import PgSQL
 
def instructions():
    print """
This program is a basic example of using PgSQL and Python to access a
PostgreSQL database.

Usage:  basic.py DSN user password

Where  DSN is "{host:{port}:}database".  Note: Items between { } are optional.
  user is the user ID to use when connecting to the database.
  password is the password to use when connecting to the database.
  """

class basic:
    """
basic - a short example of using PgSQL loosely based on the basic.java
  program supplied with the PostgreSQL jdbc driver. """

    def __init__(self, *args):
  if len(args) < 3:
      raise Exception, "Wrong number of arguments"

  dsn, user, pswd = args

  dsnc = string.split(dsn, ":")

  ldsnc = len(dsnc)

  if ldsnc == 1:
      dbase = dsnc[0]
      dsn = "::%s:%s:%s" % (dsn, user, pswd)
  elif ldsnc == 3:
      dbase = dsnc[2]
      dsn = "%s:%s:%s" % (dsn, user, pswd)
  else:
      raise Exception, "Invalid DSN value"

  # If the dbase variable is empty, then put the user name of the user
  # running the program into dbase.
  if dbase == None or dbase == "":
      if os.environ.has_key("LOGNAME"):
    dbase = os.environ["LOGNAME"]
      elif os.environ.has_key("USER"):
    dbase = os.environ["USER"]
      elif os.environ.has_key("USERNAME"):
    dbase = os.environ["USERNAME"]
      else:
    dbase = "*UNKNOWN*"

  # Connect to the database
  print "Connecting to database %s as user %s" % (dbase, user)
  self.db = PgSQL.connect(dsn)

  print "Connected ... Now creating a cursor"
  self.st = self.db.cursor()

  # Clean up from a previous run, if needed.
  self.cleanup()

  # Run the tests
  self.doexample()

  # Clean up the database.
  self.cleanup()

  print "\nNow closing the connection"
  self.st.close()
  self.db.close()

    def cleanup(self):
  try:
      self.st.execute("DROP TABLE basic")
  except:
      pass

    def doexample(self):
  print "\nRunning tests:"

  # First we need a table to store data in
  self.st.execute("CREATE TABLE basic (a int2, b int2)")

  # Now insert some data, using the cursor
  self.st.execute("INSERT INTO basic VALUES (1, 1)")
  self.st.execute("INSERT INTO basic VALUES (2, 1)")
  self.st.execute("INSERT INTO basic VALUES (3, 1)")

  # This shows how to get the OID of the just inserted row
  self.st.execute("INSERT INTO basic VALUES (4, 1)")
  insertedOID = self.st.oidValue
  print "Inserted row with oid %d" % insertedOID

  # Now change the value of b from 1 to 8
  self.st.execute("UPDATE basic SET b = 8")
  print "Updated %s rows" % (self.st.res.cmdTuples, )

  # Now delete two rows
  self.st.execute("DELETE FROM basic WHERE a < 3")
  print "Deleted %s rows" % (self.st.res.cmdTuples, )

  # Now add some rows using executemany()
  # The values (4, 2), (4, 3), and (4, 4) will be added.
  parms = []
  for i in range(2, 5):
      parms.append((4, i))
  self.st.executemany("INSERT INTO basic VALUES (%s, %s)", parms)

  # Finally perform a query on the table, showing how to access the
  # data by column number.
  print "\nPerforming a query, referencing the data by column number"
  print """i.e. 'print "    a=%d b=%d" % (res[0], res[1])'"""
  self.st.execute("SELECT a, b FROM basic")
  res = self.st.fetchone()
  while res:
      print "    a=%d b=%d" % (res[0], res[1])
      res = self.st.fetchone()

  # show how to access the data by column name.
  print "\nDisplaying results, referencing the data by column name"
  print """i.e. 'print "    a=%d b=%d" % (res["a"], res["b"])'"""
  self.st.rewind()
  res = self.st.fetchone()
  while res:
      print "    a=%d b=%d" % (res["a"], res["b"])
      res = self.st.fetchone()

  # Finally perform a query on the table, showing how to access the
  # data by column name.
  print "\nDisplaying results, using column name as an attribue"
  print """i.e. 'print "    a=%d b=%d" % (res.a, res.b)'"""
  self.st.rewind()
  res = self.st.fetchone()
  while res:
      print "    a=%d b=%d" % (res.a, res.b)
      res = self.st.fetchone()

  # Redisplay the results, showing how to access the data using the
  # result as a dictionary.
  print "\nDisplaying results, using the ResultSet as a dictionary"
  print """i.e. 'print "    a=%(a)d b=%(b)d" % res'"""
  self.st.rewind()
  res = self.st.fetchone()
  while res:
      print "    a=%(a)s b=%(b)s" % res
      res = self.st.fetchone()

if __name__ == "__main__":
    try:
  if len(sys.argv) < 4:
      raise Exception, "Wrong number of arguments"
  basic(sys.argv[1], sys.argv[2], sys.argv[3])
    except Exception, m:
  print m
  instructions()
    
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