Python dictionary query key value pair methods and examples

Finding is the focus of all our data type learning , Dictionaries are no exception , Find... From different dimensions in different ways , have everything that one expects to find . Let's learn from simple to difficult step by step Query method of dictionary .

1. Use the key to find a single value ****

dict5 = {'name': 'Tom', 'age': 18, 'love': 'python'}
print(dict5['age'])  #  Use the key to find the value 
 Return results ：18
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2. Use get() Method to find the value corresponding to the key ****

dict5 = {'name': 'Tom', 'age': 18, 'love': 'python'}
print(dict5.get('age'))   
#  utilize get The function uses the key to find the value , If key There is no return None
print(dict5.get('age', ' The default value is '))  
#  If the key doesn't exist , Set to return to default 
 Return results ：18
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3. Use setdefault() lookup ****

setdefault and get The function is almost , But if the key doesn't exist , Then the search content is put into the dictionary as a key , And set the default value , Not set to None

dict5 = {'name': 'Tom', 'age': 18, 'love': 'python'}
print(dict5.setdefault('age2'))
age2 non-existent , return None
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4. Query all keys and values and key value pairs ****

dict5 = {'name': 'Tom', 'age': 18, 'love': 'python'}
# keys()  #  Get all keys , Returns a list of 
print(dict5.keys())
# values()  #  Get all values , Returns a list of 
print(dict5.values())
# items()  #  Get all key value pairs , Returns the list of Yuanzu 
print(dict5.items())
 Return results ：
dict_keys(['name', 'age', 'love', 'age2'])\
dict_values(['Tom', 18, 'python', None])\
dict_items([('name', 'Tom'), ('age', 18), ('love', 'python'), ('age2', None)])
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From the above returned results, we find that there are three different data types ：dict_keys(),dict_values(),dict_items(), Such data cannot be accessed according to the list subscript .

v = dict5.values()
print(v[1])
 Return results ：
TypeError: 'dict_values' object is not subscriptable
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  At this time, we can change to Yuanzu and then visit

list_v = list(v)
print(list_v[1])
 Return results ：18
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