1. Dictionary copy:
dict = {'name':'wang', 'sex':'m', 'age':34, 'job':'it'}
info = dict ##Alias (Two dictionaries point to the same address space in memory)
info1 = () #shadow copy (the first layer of nested dictionary is independent, and the second layer is related below)
import copy
() #shadow copy
() #deep copy deep copy (completely independent)
Note: The association under shallow copy is only for nested objects contained in the initial state of the dictionary, and the newly added ones will not be added.
example:
>>> dict
{'info': ['a', 'b', 1, 2], 'job': 'it', 'sex': 'm', 'age': 40, 'name': 'wang'}
>>> dict_alias = dict
>>> dict_copy = (dict)
>>> dict_deep = (dict)
#Add, change, and delete object key values in the first layer, shallow copy and deep copy are not affected
>>> dict['age'] = 32
>>> del dict['sex']
>>> dict
{'info': ['a', 'b', 1, 2], 'job': 'it', 'age': 32, 'name': 'wang'}
>>> dict_alias
{'info': ['a', 'b', 1, 2], 'job': 'it', 'age': 32, 'name': 'wang'}
>>> dict_copy
{'info': ['a', 'b', 1, 2], 'job': 'it', 'age': 40, 'name': 'wang', 'sex': 'm'}
>>> dict_deep
{'info': ['a', 'b', 1, 2], 'job': 'it', 'age': 40, 'name': 'wang', 'sex': 'm'}
#Change or delete the original second layer object key value, shallow copy will be affected, while deep copy will not be affected
>>> dict['info'][2] = 100
>>> dict
{'info': ['a', 'b', 100, 2], 'job': 'it', 'age': 32, 'name': 'wang'}
>>> dict_alias
{'info': ['a', 'b', 100, 2], 'job': 'it', 'age': 32, 'name': 'wang'}
>>> dict_copy
{'info': ['a', 'b', 100, 2], 'job': 'it', 'age': 40, 'name': 'wang', 'sex': 'm'}
>>> dict_deep
{'info': ['a', 'b', 1, 2], 'job': 'it', 'age': 40, 'name': 'wang', 'sex': 'm'}
#Add the second layer of objects, shallow copy and deep copy are not affected
>>> dict['new'] = {'a':1, 'b':2, 'c':5}
>>> dict
{'info': ['a', 'b', 100, 2], 'name': 'wang', 'age': 32, 'job': 'it', 'new': {'a': 1, 'c': 5, 'b': 2}}
>>> dict_alias
{'info': ['a', 'b', 100, 2], 'name': 'wang', 'age': 32, 'job': 'it', 'new': {'a': 1, 'c': 5, 'b': 2}}
>>> dict_copy
{'info': ['a', 'b', 100, 2], 'job': 'it', 'age': 40, 'name': 'wang', 'sex': 'm'}
>>> dict_deep
{'info': ['a', 'b', 1, 2], 'job': 'it', 'age': 40, 'name': 'wang', 'sex': 'm'}
2. Built-in function description:
__name__: Returns main when the main file, otherwise it returns the file name, which can be used to determine whether the main file or the import module is said to be;
__file__: The absolute path to the file;
__doc__: Comments and descriptions at the beginning of the file
example:
'''
created by 2015-12-18
@author: kevin
'''
if __name__ == '__main__':
print('this is main file')
print(__file__)
print(__doc__)