python中的字典用法示例详解编程语言

#!/usr/bin/env python 
# 
# [SNIPPET_NAME: Dictionaries 101] 
# [SNIPPET_CATEGORIES: Python Core] 
# [SNIPPET_DESCRIPTION: Basic and not so basic dictionary operations] 
# [SNIPPET_AUTHOR: Bruno Girin <[email protected]>] 
# [SNIPPET_LICENSE: GPL] 
  
# This snippet demonstrates how the basics on dictionaries: how to create, add, 
# remove items, get items, iterate, etc. 
  
# 
# First, let's create simple dictionary. A dictionary (called map in Java hash 
# in perl) is similar to a list with the difference that the key doesn't 
# have to be an integer, it can be anything. 
# 
# A dictionary is enclosed in curly brackets and each key is mapped to its 
# corresponding value with a colon. So in the dictionary below, we associate 
# the key Karmic with the value 9.10 and so on for the 5 pairs. 
# 
print "Create a simple dictionary" 
simpleDict = {"Karmic": "9.10", "Lucid": "10.04", "Hardy": "7.10", 
              "Jaunty": "8.10", "Intrepid": "8.04"} 
# print it 
print simpleDict 
# 
# Another way to create a dictionary is to zip two lists containing the keys 
# and values in the same order to create a list of tuples, which we can then 
# pass to the dict() method to create a dictionary. 
# 
myKeys = ['Feisty', 'Edgy', 'Dapper'] 
myValues = ['7.04', '6.10', '6.06'] 
otherDict = dict(zip(myKeys, myValues)) 
print otherDict 
# 
# Interrogate the dictionary. It works exactly the same as with a list, with the 
# exception that the key is no longer an integer. 
# 
print "/nInterrogate the dictionary" 
# get for value for key Jaunty 
print simpleDict['Jaunty'] 
# get the length of the dictionary 
print len(simpleDict) 
# check if the dictionary contains the key Lucid 
print 'Lucid' in simpleDict 
print 'Breezy' in simpleDict 
# 
# Modify the dictionary 
# 
print "/nModify the dictionary" 
# add another item 
simpleDict['Hoary'] = '5.06' 
print simpleDict 
# oops! let's sort this out by replacing in place 
simpleDict['Hoary'] = '5.04' 
print simpleDict 
# update the dictionary with mappings from another one 
simpleDict.update(otherDict) 
print simpleDict 
# remove an item from the list (Hardy should not be in the list anymore) 
del simpleDict['Hoary'] 
print simpleDict 
# 
# Iterate over the dictionary. A dictionary doesn't enforce a natural ordering 
# like a list but we can still iterate over it in multiple ways. 
# However, note that when you iterate, the order in which the items are 
# retrieved is unspecified. 
# 
print "/nIterate over the dictionary" 
print "/nby keys" 
for k in simpleDict.keys(): 
    print k 
print "/nby values" 
for v in simpleDict.values(): 
    print v 
print "/nby items" 
# note the syntax to retrieve the key and value at the same time 
for k, v in simpleDict.items(): 
    print k, '=>', v 
# 
# More interesting transformations from list to dictionary and vice versa. 
# List comprehension allow you to do a lot of interesting stuff, in particular 
# tranforming lists into dictionaries and the other way around. 
# 
print "/nList to dictionary and vice versa" 
# First, let's transform our dictinary into a list of tuples 
simpleList = [(k, v) for k, v in simpleDict.items() ] 
print simpleList 
# Create a map from a list with the list's entry as key and the index as value 
# This method takes advantage of another way of creating a map, using a 
# sequence of tuples, so in practice, we create a tuple for each item in the 
# list, create a list from all the tuples using a list comprehension and pass 
# it as argument to the dict() function 
cityList = ['London', 'Paris', 'New York', 'Tokyo'] 
cityDict = dict([(x, i) for i, x in enumerate(cityList)]) 
print cityDict 
# Create a map from a number to its square 
squareDict = dict([(x, x * x) for x in range(1, 10)]) 
print squareDict