This is the personal python tutorial for quick reference. If you read this article by chance, you better skip or ignore it. It won’t fit you, because it’s just a collections of some pieces of my notes when I learning python.

Get help

import this
# then read the output sentences carefully
import os
>>> dir(os)
>>> help(os.chown)
>>> print(os.__doc__)

Four kind of most important data type, String, List, Tuple, Dictionary

variables in python are not necessary to be declared, assign a value before use it, at the same time, you cannot refer to a variable you did not assign

String
s = 'Hello'
  • immutable
  • double quote or single quote, no big difference between them, but single quote is more common in python
  • use the syntax s[m:n] to refer the element start from m to n (not including n)
  • add the prefix ‘r’ to create a raw string, which can disable the interpretation of special character
List
l = [1, 2, 3]
  • mutable
  • bracket
  • use ‘for’ to iterate a list
>>> for i in l:
...     print i
  • check the existing of a element in a list
>>> if 1 in l:
...     print '1 is one element of l'
  • conversion between list and string, s.join and l.split
Tuple
t = (1, 2, 4, 3)
  • immutable
  • parenthesis
  • other operations are very similar with list, but more efficient
  • a cool feature of tuple, assign value to multiple variable at the same time, (x, y) = (1, 3)
  • c style formatted output, 'x = %d, y = %d' % (2, 3)
Dictionary
d = {}
d['a'] = 'alpha'
d['o'] = 'omega'
d['e'] = 'gamma'
  • a combination of keys and values, think it as map, hashmap, etc.
  • d['x'] will raise KeyError, but d.get('x') just return None
  • check the existence of a key, 'x' in d
  • d.keys() and d.values() will return a list of keys and a list of values respectively
  • d.items() will return key-value pair as a list of tuple

File operations

read from file
>>> f = open('/etc/passwd', 'rU')
>>> for line in f:
...     print line
write to a file
>>> f = open('/home/mutter/test.txt', 'w+')
>>> f.write('a python generated string')
>>> f.flush()
>>> f.close()

Regular expression

import re
match = re.search(pattern, text)
if match:
    match.group()

re.findall(pattern, text)
# return a matched list

if pattern has group separator, we can use match.group(1), match.group(2), ... to refer the results.

interaction between os and other utils

import os
import sys
import shutil
import commands

when import a module, python interpreter will evaluate the entire module file from beginning to end.

Exception handling

>>> try:
...     d['x']
... except KeyError:
...     print 'key error'
... finally:
...     print 'I\'m finally'
...

HTTP request

import urllib
uf = urllib.urlopen('http://cn.bing.com')
uf.read()
urllib.urlretrieve('http://cn.bing.com', 'bing.html')