python字典dict中常用内置函数的使用

dict = {'a':10, 'b':20, 'c':30}
dict.clear()
print(dict) # {}

dict = {'a':10, 'b':20, 'c':30}
print(dict.get('c')) # 30
print(dict.get('g')) # None
print(dict.get('g', -1)) # -1 指定可选参数

dict = {'a':10, 'b':20, 'c':30}
dict.items() # dict_items([('a', 10), ('b', 20), ('c', 30)])
list(dict.items()) # [('a', 10), ('b', 20), ('c', 30)]
list(dict.items())[1] # ('b', 20)
list(dict.items())[1][0] # 'b'

dict = {'a':10, 'b':20, 'c':30}
dict.values() # dict_values([10, 20, 30])
list(dict.values()) # [10, 20, 30]

# 即使值重复，也会被多次返回
dict2 = {'a':10, 'b':10, 'c':30}
list(dict2.values()) # [10, 10, 30]

dict = {'a':10, 'b':20, 'c':30}
dict.pop('b') # 20
print(dict) # {'a': 10, 'c': 30}
dict.pop('g')
'''
Traceback (most recent call last):

  File "<iPython-input-20-a81e983a7be0>", line 1, in <module>
    dict.pop('g')

KeyError: 'g'
'''
dict.pop('g', -1) # -1

dict = {'a':10, 'b':20, 'c':30}
dict.popitem() # ('c', 30)
print(dict) # {'a': 10, 'b': 20}
dict.popitem() # ('b', 20)
print(dict) # {'a': 10}
dict.popitem() # ('a', 10)
print(dict) # {}
dict.popitem()
'''
Traceback (most recent call last):

  File "<ipython-input-28-7e744445e3D2>", line 1, in <module>
    dict.popitem()

KeyError: 'popitem(): dictionary is empty'
'''

dict = {'a':10, 'b':20, 'c':30}
dict2 = {'b':200, 'd':400}
dict.update(dict2)
print(dict) # {'a': 10, 'b': 200, 'c': 30, 'd': 400}