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python dictionary definition
Dictionary is another mutable container model and can store any type of object.
Each key-value key=>value pair in the dictionary is separated by colon :. Each key-value pair is separated by comma,. The entire dictionary is included in curly braces {}. The format is as follows:
d = {key1 : value1, key2 : value2 }
The key is generally unique. If the last key-value pair is repeated, the previous one will be replaced. The value does not need to be unique.
>>>dict = {'a': 1, 'b': 2, 'b': '3'} >>> dict['b'] '3' >>> dict {'a': 1, 'b': '3'}
Other common ways to create a dictionary in Python:
Dynamic assignment of key values
>>> d ={} >>> d['name'] = 'Allen' >>> d {'name': 'Allen'}
If needed This method is more appropriate if you dynamically create one field of a dictionary at a time.
Dictionary key-value table
>>> c = dict(name='Allen', age=14, gender='male') >>> c {'gender': 'male', 'age': 14, 'name': 'Allen'}
Because this form has simple syntax and is less error-prone, it is very popular.
This form requires less code than constants, but the keys must all be strings, so the following code will report an error:
>>> c = dict(name='Allen', age=14, gender='male', 1='abcd') File "<stdin>", line 1 SyntaxError: keyword can't be an expression
Dictionary key value tuple table
>>> e=dict([('name','Allen'),('age',21),('gender','male')]) >>> >>> >>> e {'gender': 'male', 'age': 21, 'name': 'Allen'}
This method is useful if you need to gradually build the keys and values into a sequence while the program is running.
The values of all keys are the same or assigned initial values
>>> f=dict.fromkeys(['height','weight'],'normal')>>> f {'weight': 'normal', 'height': 'normal'}
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