字典操作

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1.Dictionaries

purse = dict()
purse['money'] = 12
purse[''candy] = 3
purse['tissues'] = 75
print (purse)
>>> ['money':12, 'tissues': 75,'candy':3]

2. get method for dictionaries

counts = dict()
names = ['csev','cwen','csev','zqian','cwen']
for name in names:
  counts[name] = counts.get(name,0) +1
print(counts)

3.Program

//计算文中单词出现的频数
counts = dict()
print ('Enter a line of text:')
line = input("")

words = line.split()
print ('Words:',words)

print ('Counting')
for name in words:
  counts[name] = counts.get(name,0) +1
print ('Counts',counts)

4. for loop in dictionaries

counts = ('chuck':1,'fred':42,'jan':100)
for key in counts：
  print (key,counts[key])
>>> jan 100
>>> chuck 1
>>> fred 42

5. Retrieving lists of Keys and Values

jjj = {'chuck':1,'fred':42,'jan':100}
print (list(jjj))
>>> ['jan','chuck','fred']
print (jjj.keys())
>>> ['jan','chuck','fred']
print (jjj.values())
>>> [100,1,42]
print (jjj.items())
>>> [('jan',100),('chuck',1),('fred',42)]

6.Two Iteration Variables!

jjj = {'','',''}
for aaa,bbb in jjj.items():
  print(aaa,bbb)

planets = ['Mercury', 'Venus', 'Earth', 'Mars', 'Jupiter', 'Saturn', 'Uranus', 'Neptune']
planet_to_initial = {planet: planet[0] for planet in planets}
planet_to_initial
>>> {'Earth': 'E',
   'Jupiter': 'J',
   'Mars': 'M',
   'Mercury': 'M',b
   'Neptune': 'N',
   'Saturn': 'S',
   'Uranus': 'U',
   'Venus': 'V'}