======================= swap col 3 and 4
outfile = file("out.txt", "w")
for line in file("in.txt"):
    data = line.rstrip('\n').split('\t')
    data[3],data[4] = data[4],data[3]
    outfile.write('\t'.join(data))
======================= pydoc
pydoc sys                    # document a built-in module
pydoc copy                   # document a module written in Python
pydoc types                  # document a module written in Python
pydoc abs                    # document a built-in function
pydoc repr.Repr              # document a single class
pydoc -k mail                # keyword search like man -k
pydoc -p 6789                # start a web server at http://localhost:6789/

>>> from pydoc import help
>>> help("getopt.getopt")    # document something you haven't imported
>>> import calendar
>>> help(calendar)           # document a live object

======================= quick sort
def qsort(L):
    if len(L) <= 1: return L
    return qsort( [ lt for lt in L[1:] if lt < L[0] ] )  +  \ 
              [ L[0] ]  +  qsort( [ ge for ge in L[1:] if ge >= L[0] ] )

======================= extract email addresses from files
import sys,re
print '\n'.join(re.findall('([\w\.\-]+@[\w\.\-]+)',sys.stdin.read()))

======================= gnuplot with the popen function
import os
f=os.popen('gnuplot', 'w')
print >>f, "set yrange[-300:+300]"
for n in range(300):
	print >>f, "plot %i*cos(x)+%i*log(x+10)" % (n,150-n)
f.flush()
======================= pexpect
import pexpect
child = pexpect.spawn ('ftp ftp.openbsd.org')
child.expect ('Name .*: ')
child.sendline ('anonymous')
child.expect ('[pP]assword:')
child.sendline ('noah@example.com')
child.expect ('ftp> ')
child.sendline ('cd pub')
child.expect('ftp> ')
child.sendline ('get ls-lR.gz')
child.expect('ftp> ')
child.sendline ('bye')
-----------------------
child.expect('password:')
child.sendline (my_secret_password)
# We expect any of these three patterns...
i = child.expect (['Permission denied', 'Terminal type', '[#\$] '])
if i==0:
    print 'Permission denied on host. Can't login'
    child.kill(0)
elif i==2:
    print 'Login OK... need to send terminal type.'
    child.sendline('vt100')
    child.expect ('[#\$] ')
elif i==3:
    print 'Login OK.'
    print 'Shell command prompt', child.after
....
child.expect('password:', timeout=120)
....
child = pexpect.spawn ('ssh user@example.com')
child.expect ('assword')
child.sendline ('mypassword')
======================= ipython
----------------------- profiles
ipython -p <profile name>
----------------------- edit
edit -x
----------------------- history
hist -n

----------------------- macros
macro print_l 2
Macro `print_l` created. To execute, type its name (without quotes).
Macro contents:
for i in l:
    print i

----------------------- System Shell Access
In the default IPython profile, the Unix shell commands cd, pwd, and ls all
work like they do from a bash shell. To execute any other shell commands,
prepend a ! or !! to them. Use the %sc and %sx magic words to capture the
output from shell commands.

Starting IPython with a -p pysh flag will cause IPython to accept and execute
any commands in the user's $PATH, while at the same time allowing access to
all Python modules as well as all Python keywords and built-in functions.

ipython -p pysh

for i in range(500):
    mkdir d_${i}_d

will create 500 directories
======================= GNU plot
import os
f=os.popen('gnuplot', 'w')
print >>f, "set yrange[-300:+300]"
for n in range(300):
    print >>f, "plot %i*cos(x)+%i*log(x+10)" % (n,150-n)
f.flush()
======================= SQLite
http://www.sebsauvage.net/python/snyppets/index.html
#!/usr/bin/python
# -*- coding: iso-8859-1 -*-
from sqlite3 import dbapi2 as sqlite

# Create a database:
con = sqlite.connect('mydatabase.db3')
cur = con.cursor()

# Create a table:
cur.execute('create table clients (id INT PRIMARY KEY, name CHAR(60))')

# Insert a single line:
client = (5,"John Smith")
cur.execute("insert into clients (id, name) values (?, ?)", client )
con.commit()
 
# Insert several lines at once:
clients = [ (7,"Ella Fitzgerald"),
            (8,"Louis Armstrong"),
            (9,"Miles Davis")
          ]
cur.executemany("insert into clients (id, name) values (?, ?)", clients )
con.commit()

cur.close()
con.close()
----------------------- usage
#!/usr/bin/python
# -*- coding: iso-8859-1 -*-
from sqlite3 import dbapi2 as sqlite

# Connect to an existing database
con = sqlite.connect('mydatabase.db3')
cur = con.cursor()
 
# Get row by row
print "Row by row:"
cur.execute('select id, name from clients order by name;')
row = cur.fetchone()
while row:
    print row
    row = cur.fetchone()

# Get all rows at once:
print "All rows at once:"
cur.execute('select id, name from clients order by name;')
print cur.fetchall()

cur.close()
con.close()

----------------------- hints
Hint 1: If you use sqlite.connect(':memory:'), this creates an in-memory database. As there is no disk access, this is a very very fast database.
 (But make sure you have enough memory to handle your data.)
 
 
 Hint 2: To make your program compatible with Python 2.5 and Python 2.4+pySqlLite, do the following:
 
try: 
     from sqlite3 import dbapi2 as sqlite    # For Python 2.5
 except ImportError:
     pass
 
 if not sqlite:
     try:
         from pysqlite2 import dbapi2 as sqlite  # For Python 2.4 and pySqlLite
     except ImportError:
         pass
 
 if not sqlite:  # If module not imported successfully, raise an error.
     raise ImportError, "This module requires either: Python 2.5 or Python 2.4 with the pySqlLite module (http://initd.org/tracker/pysqlite)"
 
 # Then use it
 con = sqlite.connect("mydatabase.db3")
 ...
======================= getopt
import sys
 import getopt
 
 if __name__ == "__main__":
 
     opts, args = None, None
     try:
         opts, args = getopt.getopt(sys.argv[1:], "hco:",["help", "capitalize","output="])
     except getopt.GetoptError, e:
         raise 'Unknown argument "%s" in command-line.' % e.opt
 
     for option, value in opts:
         if option in ('-h','--help'):
             print 'You asked for the program help.'
             sys.exit(0)            
         if option in ('-c','--capitalize'):
             print "You used the --capitalize option !"
         elif option in ('-o','--output'):
             print "You used the --output option with value",value
 
     # Make sure we have our mandatory argument (file)
     if len(args) != 1:  
         print 'You must specify one file to process. Use -h for help.'
         sys.exit(1)
     
     print "The file to process is",args[0]
     
     # The rest of the code goes here...
======================= date, time 
import datetime,time
def dateDiffInSeconds(date1, date2):
    timedelta = date2 - date1
    return timedelta.days*24*3600 + timedelta.seconds

date1 = datetime.datetime(2006,02,17,15,30,00)
date2 = datetime.datetime(2006,05,18,11,01,00)
print dateDiffInSeconds(date1,date2)
-----------------------
time.strptime() converts the string to a struct_time tuple.
time.mktime() converts this tuple into seconds (elasped since epoch, C-style).
datetime.fromtimestamp() converts the seconds to a Python datetime object.
======================= Columns to rows (and vice-versa)
table = [  ('Person', 'Disks', 'Books'),
            ('Zoe'   ,     12,      24 ),
            ('John'  ,     17,       5 ),
            ('Julien',      3,      11 )
         ]         
 
 print zip(*table)
======================= 
======================= 
=======	convert a GIF to python source code
import base64
print "icon='''\\\n" + base64.encodestring(open("icon.gif", "rb").read()) + "'''"

=======	import datetime
now = datetime.datetime(2003, 8, 4, 12, 30, 45)
print now
print repr(now)
print type(now)
print now.year, now.month, now.day
print now.hour, now.minute, now.second
print now.microsecond

d = datetime.date(2003, 7, 29)
print d
print d.year, d.month, d.day
print datetime.date.today()

t = datetime.time(18, 54, 32)
print t
print t.hour, t.minute, t.second, t.microsecond

now = datetime.datetime.now()
d = now.date()
t = now.time()
print now
print d, t
print datetime.datetime.combine(d, t)
------- convert a string date ("2006-05-18 19:35:00") into a datetime object
import datetime,time
dt = datetime.datetime.fromtimestamp(time.mktime(time.strptime(stringDate,"%Y-%m-%d %H:%M:%S")))
------- difference between two dates, in seconds
def dateDiffInSeconds(date1, date2):
    timedelta = date2 - date1
    return timedelta.days*24*3600 + timedelta.seconds

date1 = datetime.datetime(2006,02,17,15,30,00)
date2 = datetime.datetime(2006,05,18,11,01,00)
print dateDiffInSeconds(date1,date2)

=======	import import gzip
file = gzip.GzipFile("samples/sample.gz")
print file.read()

-----------
class gzipFile(gzip.GzipFile):
    # adds seek/tell support to GzipFile

    offset = 0

    def read(self, size=None):
        data = gzip.GzipFile.read(self, size)
        self.offset = self.offset + len(data)
        return data

    def seek(self, offset, whence=0):
        # figure out new position (we can only seek forwards)
        if whence == 0:
            position = offset
        elif whence == 1:
            position = self.offset + offset
        else:
            raise IOError, "Illegal argument"
        if position < self.offset:
            raise IOError, "Cannot seek backwards"

        # skip forward, in 16k blocks
        while position > self.offset:
            if not self.read(min(position - self.offset, 16384)):
                break

    def tell(self):
        return self.offset

#
# try it

file = gzipFile("samples/sample.gz")
file.seek(80)

print file.read()

======= import curses

text = [
    "a very simple curses demo",
    "",
    "(press any key to exit)"
]

# connect to the screen
screen = curses.initscr()

# setup keyboard
curses.noecho() # no keyboard echo
curses.cbreak() # don't wait for newline

# screen size
rows, columns = screen.getmaxyx()

# draw a border around the screen
screen.border()

# display centered text
y = (rows - len(text)) / 2

for line in text:
    screen.addstr(y, (columns-len(line))/2, line)
    y = y + 1

screen.getch()
curses.endwin()
======= file counter
class Counter:
    def __init__(self):
        self.count = 0
    def inc(self, n=1):
        self.count += n

def count_names(count, dir, flist):
    count.inc(len(flist))

count = Counter()
os.path.walk("/", count_names, count)

print count.count,"files in all"

======= Fetch, read and parse a RSS 2.0 feed in 6 lines
import urllib, sys, xml.dom.minidom
address = 'http://www.sebsauvage.net/rss/updates.xml'
document = xml.dom.minidom.parse(urllib.urlopen(address))
for item in document.getElementsByTagName('item'):
    title = item.getElementsByTagName('title')[0].firstChild.data
    print "Title:", title.encode('latin-1','replace')
======= redirect standard error to a file
import sys

class myLogger:
    def __init__(self):
        pass
    def write(self,data):
        file = open("mylog.txt","a")
        file.write(data)
        file.close()

sys.stderr = myLogger()   # Use my class to output errors instead of the console.

print 5/0   # This will trigger an exception
======= Parsing: IP
ipRegExC = r"\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}"
ipRegEx = re.compile(ipRegExC)
======= host info
import os

kernel, hostname, release, version, hardware = os.uname()

import socket

address = socket.gethostbyname(hostname)
hostname = socket.gethostbyaddr(address)
hostname, aliaslist, ipaddrlist = socket.gethostbyname_ex(hostname)

======= socket
import socket
import os, os.path

if os.path.exists("/tmp/mysock"):
    os.remove("/tmp/mysock")
        
server = socket.socket(socket.AF_UNIX, socket.SOCK_DGRAM)
server.bind("/tmp/mysock")

client = socket.socket(socket.AF_UNIX, socket.SOCK_DGRAM)
client.connect("/tmp/mysock")
-------
ipaddr, port = s.getpeername()
hostname, aliaslist, ipaddrlist = socket.gethostbyaddr(ipaddr)
ipaddr = socket.gethostbyname('www.python.org')
# '194.109.137.226'
hostname, aliaslist, ipaddrlist = socket.gethostbyname_ex('www.python.org')
# ('fang.python.org', ['www.python.org'], ['194.109.137.226'])
socket.gethostbyname_ex('www.google.org')
# ('www.l.google.com', ['www.google.org', 'www.google.com'], 
#  ['64.233.161.147','64.233.161.104', '64.233.161.99'])

======= 
import urllib2
urllib2.urlopen('http://whatismyip.org').read()
-----
import uuid
uuid.getnode()
67474971543L
hex(uuid.getnode())
======= 
=======