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Standard libraries

OS

System call without reading output:
status = os.system('your commandline here')
System call with reading output:
content = os.popen('your command line here')
print content.read()
Alternative way using commands module:
import commands
out = commands.getoutput('ls -l')


file

Method seek() can be used to set file object's offset. fin.seek(0) will point the file object to start of the file.

Data compression (gzip, bz2)

Read and write data into compressed files using gzip or bzip2.
>>> import gzip
>>> fin = gzip.GzipFile('file.gz')
>>> fout = gzip.GzipFile('out.gz','w')
(following are similar with regular file objects)

>>> import bz2
>>> fin = bz2.BZ2File('a.bz2')
(following are similar with regular file objects)

urllib

Open an URL address and check HTTP status code:
url_handle = urllib.urlopen('http://localhost')
print url_handle.getcode()

Special characters needs to be escaped before they enter the URL string:
a = 'Epigenomics Workshop - 9/09'
print urllib.quote(a)
print urllib.quote_plus(a) # more safe

ftplib

from ftplib import FTP
ftp = FTP('ftp.ncbi.nih.gov')
ftp.login()
contents = []
# change directory to
ftp.cwd('/pub/geo/DATA/supplementary/samples/GSM537nnn/GSM537699/')

# look what files exist under this dir
# a callback function will be used to process returned contents
ftp.dir(lambda x: contents.append(x))
for cont in contents:
    print cont


# and then look somewhere else
ftp.cwd('/somewhere/else/')
ftp.dir(lambda x: contents.append(x))
print contents[-1]

Encryption

from hashlib import sha1
token_str = sha1('a secret string to encrypt').hexdigest()
print token_str

Regular expression

import re
exp = re.compile(r'\[(..?)\]')
a = '[12],[23],[34],,,'
for i in exp.findall(a):
  print i

CGI

import cgi
print "Content-Type: application/json"
# or "text/html"
print

form = cgi.FieldStorage()

if "trigger1" in form:
       value = form["trigger1"].value
       # do something...


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