python字典 Dictionary

#-*- coding:UTF-8 -*-

tel={'jack':4098,'sape':4139}
tel['guido']=4127

print   tel
#{'sape': 4139, 'jack': 4098, 'guido': 4127}

print   tel['jack']
#4098
#如果key不存在会报错，避免key不存在的错误，有两种办法，一是通过in判断key是否存在
print   'guido' in  tel     
#True

#二是通过dict提供的get方法，如果key不存在，可以返回None，或者自己指定的value
print  tel.get('jilk')
print  tel.get('jilk',-1)
#None
#-1


del tel['sape']
tel['irv']=4127
print  tel
#{'jack': 4098, 'irv': 4127, 'guido': 4127}

#要删除一个key，用pop(key)方法，对应的value也会从dict中删除
tel.pop('irv')
print  tel
#{'jack': 4098, 'guido': 4127}

print  tel.keys()
#['jack', 'guido']



#The dict() constructor builds dictionaries directly from sequences of key-value pairs:
#dict() 函数用于创建一个字典。返回一个字典
print   dict([('sape',4139),('guido',4127),('jack',4098)])   
#{'sape': 4139, 'jack': 4098, 'guido': 4127}

print {x:x**2 for x in  (2,4,6)}   
#{2: 4, 4: 16, 6: 36}

print  dict(sape=4139,guido=4127,jack=4098)
#{'sape': 4139, 'jack': 4098, 'guido': 4127}