本文包含了python字典的各种用法，字典在python中的重要性不言而喻

#!/usr/bin/env python

#

# [代码名字: Dictionaries 101]

# [代码分类: Python Core]

# [代码描述: Basic and not so basic dictionary operations]

# [代码协议: 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

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