python 学习笔记 2

 第二章 元组和列表

• Example 1

• x='abc';y=10;z=100.2;

• arr1=[x,y,30,z] # define an array

• arr2=[] #define the empty array

• print(x[0]) # output “a”, string is also an array

• print(x[-1]) # output “c”, -1 means n-1 (n is the length)

• print(x[-2]) # ouput 'b', -2, means n-2

• print(len(arr1)) # output 4

• 2 dimentional array arr3=[[10,20,30],['a', 'b', 'c']]

• print(arr3[0] ) # [10,20,30]

• print(arr3[0][1]) # 20

• ['a','b'] * 2 # ['a', 'b', 'a', 'b']

• ['a', 'b'] + [10] # ['a', 'b', 10]

• numbers = [1,2,3,4,5,6,7,8,9,10]; print(numbers[3:6]); # 4,5,6 , index 3,4 and 5

• numbers = [1,2,3,4,5,6,7,8,9,10]; print(numbers[-3:-1]); # 8, 9

• numbers = [1,2,3,4,5,6,7,8,9,10]; print(numbers[-3:]); # 8, 9,10

• numbers[:] ==> numbers

• numbers[:3] ==> numbers[0:3]

• *  numbers[1:8:2] ==> 2 is steps
  *  check whether some element is in a list : 2 in [1,2,3] ==> true ; 2 in ['1', '2', '3'] ==> false
  *  use min() and max() to get the min value and the max value from a list, 
  e.g., min([2,1,5]) ==> 1 ; max([2,1,5]) ==> 5
  ** if the element in the array( or list) is not number, an error will report
  e.g., min([2, '1', 5]) ==> error
  *  change string to list ==> list(strVar)
  e.g., x=list('hello') ==> x is ['h', 'e', 'l', 'l', 'o']
  *  delete one element from list
  e.g., x is ['h', 'e', 'l', 'l', 'o'] , and run del x[2] ==> x is ['h', 'e', 'l', 'o']
  *  assign by slice :x=['h', 'e', 'l', 'l', 'o']; x[1:3] = list('ABCD') ==> x=['h', 'A', 'B', 'C', 'D', 'l', 'o']
  *  use x[2:5]=[] to remove the elements 2, 3, 4
  *  x is ['e', 'A', 'B', 'C'], call x[0::2]=[100, 200]
     result : x is [100, 'A', 200, 'C']
  *  use append x is [100, 'A', 200, 'C'], x.append(200), new x is [100, 'A', 200, 'C', 200]
  *  x.count(200) is 2 ==> count means count the number of the input value
  *  x.extend() x.extend([5,6]) ==> result x is [100, 'A', 200, 'C', 200, 5, 6]
  *  index(), means get the index of a specific value x.index(5) ==> 5, x.index('A') ==> 1
  if the value to search by index() doesn't exist, an error will report
  *  insert an element x.insert(3, 'four') ==> insert value 'four' to position 3
  *  pop() remove and return the last value; x.pop(2) return the x[2] and remove it from x
  *  x.remove('C') will remove the first 'C' from x ( only remove one element, not all the element matched the criteria) , if the element doesn't exist, an error will report
  *  revert a list x.revert()
  *  sort the list x.sort() ==> all the elements should be the same type so that they could be sort
  *  sort by the length of the string ==> x.sort(key=len)
  *  revert sort ==> x.sort(reverse=True)
  *  sort by specific function ==> x.sort(cmpfunc)
  *  元组 (1,2,3)
  *  empty tuple ==> () ; one element tuple ==> (2,)
  *  change list to tuple : tuple([1,2,3])
  *  some functions used  by list or tuple
      **  cmp(x,y) compare x and y, return -1, 0, 1
      **  len(seq), calculate the length of seq
      **  list(seq), convert seq to list
      **  tuple(seq), convert seq to tuple
      **  max(args), min(args)
      **  reversed(seq)
      **  sorted(seq)