Python I

1. Unix Shell Scripts
     #! /usr/bin/env python
     ...script goes here...

2. Pause the script
    raw_input()

3. Python built in types
    Numbers      1234, 3.14, 999L, 3+4j, Decimal
    Strings          'spam', "guido's"
    Lists              [1,[2,'three'],4]
    Dictionaries   {'food':'spam', 'taste':'yum'}
    Tuples            (1,'spam',r,'U')
    Files               myfile=open('eggs','r')
    Other types    Sets, types,None,Booleans

4. math module contains more advanced numeric functions
    import math
    math.pi
    math.sqrt(85)

5. random module performs random number generation and random selections
    import random
    random.random()
    random.choice([1,2,3,4])

6. String in python
     len(S) #length
     S[0]    #the first character of string S
     S[-1]   #the last item of string S
     S[1:3]  #substring of S, includes S[1] and S[2], without S[3]
     S[0:]
     S[:3]
     S[:-1]
     S[:]
     s1+s2   # concatenation
     s*8       # repetition
   Notice: string objects in python are immutable, we can never change the content of the string, only can we create new strings.
    s[0]='z'  will cause error
    s='z'+s[1:] is the correct way
    s.find('pa')  # find substring
    s.replace('pa','XYZ') #replace
    These functions don't change the original string.
    s.split(',')
    s.upper()
    s.isalpha() #content tests: isalpha, isdigit, etc
    s.rstrip() #remove whitespace on the right side

7. use dir(object) function to see what methods it has.
 
8. to ask about what each function does, use help(object.function)

9. show the value of character, ord('\n')

10. re module for regular expression
    import re
    match=re.match('/(.*)/(.*)/(.*)','/usr/home/jack')
    match.groups() #output is ('usr','home','jack')

11. List is mutable, i.e. changed in place unlike string.
     l[0]='123'
     l.append('NI')
     l.pop(2)
     l.sort()
     l.reverse()

12. arbitrary nesting is supported
     M=[[1,2],[3,4]]
     M[1]    # result is [3,4]
     M[0][1]   # result is 2

13. List comprehension - accessing columns
     c=[row[1] for row in M]  # result is [2,4]