Python: Type conversion

Abstract: conversion among list, dictionary.

1. Convert the list to dictionary type using the function zip() and dict()

>>> a=range(10) #numeric

>>> d=dict(zip(a,a))

>>> print d

{0: 0, 1: 1, 2: 2, 3: 3, 4: 4, 5: 5, 6: 6, 7: 7, 8: 8, 9: 9}

>>> a=['a','b','c'] #string type

>>> b=['a1','b1','c1']

>>> print zip(a,b)

[('a', 'a1'), ('b', 'b1'), ('c', 'c1')]

>>> print dict(zip(a,b))

{'a': 'a1', 'c': 'c1', 'b': 'b1'}

In the example, the indexes and elements of the list are used as the keys and values of the dictionary.

>>> a=['1','a12', 'b34']

>>> d={key:value for key, value in enumerate(a)}

>>> print d

{0: '1', 1: 'a12', 2: 'b34'}

2. Subset of a list

>>> a=range(10)

>>> a

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

>>> a[:3] #the first three elements

[0, 1, 2]

>>> a[:-3] #remove the last three elements

[0, 1, 2, 3, 4, 5, 6]

>>> a[-3:] #the last three elements

[7, 8, 9]

>>> a[2:5] #Three continuous elements in the middle

[2, 3, 4]

writing date: 20150522