python deepcopy
>>> import copy
>>> nums = [1, 2, 3]
>>> data = {'a': 10, 'b': nums}
>>> data
{'a': 10, 'b': [1, 2, 3]}
>>> data_copy = copy.copy(data)
>>> data_deep = copy.deepcopy(data)
>>> data_copy
{'a': 10, 'b': [1, 2, 3]}
>>> data_deep
{'a': 10, 'b': [1, 2, 3]}
>>> data_copy['a'] += 2
>>> nums[1:1] = [254]
>>> data
{'a': 10, 'b': [1, 254, 2, 3]}
>>> data_copy
{'a': 12, 'b': [1, 254, 2, 3]}
>>> data_deep
{'a': 10, 'b': [1, 2, 3]}python copy variable
>>> import copy
>>> a = 0
>>> b = 2
>>> a = copy.copy(b)
>>> b += 1
>>> a
2
>>> b
3python copy class object
"""
I've read that there are problems with this approach, but it never let me down
"""
import copy
class Dummy:
def __init__(self, signature = 1, some_list = []):
self.signature = signature
self.list = some_list
def change_signature(self):
self.signature += 1
def change_list(self):
self.list[0][0] += 1
def naive_test():
print('---> Naive Copy Test')
dummy1 = Dummy(1)
#dummy2 points to dummy1
dummy2 = dummy1
if dummy1.signature == dummy2.signature:
print ('tDummy instances are the same')
dummy1.change_signature()
if dummy1.signature == dummy2.signature:
print ('tDummy 'copy' changed after changing the original. They are still the same.')
def shallow_copy_test():
print('n---> Shallow Copy Test')
dummy1 = Dummy(1, [[1,2],[3,4]])
#Create shallow copy
dummy2 = copy.copy(dummy1)
if dummy1.signature == dummy2.signature:
print ('tDummy instances are the same')
dummy1.change_signature()
if dummy1.signature != dummy2.signature:
print ('tDummy copy didn't change after changing the original. They are now different.')
dummy1.change_list()
if dummy1.list == dummy2.list:
print('tBut their lists change together! This is because the copy only made copies of the original instance's higher level list, but it is a list of lists, so each instance points to two different lists which, in turn, point to the SAME lists')
def deep_copy_test():
print('n---> Deep Copy Test')
dummy1 = Dummy(1, [[1,2],[3,4]])
#Create deep copy
dummy2 = copy.deepcopy(dummy1)
if dummy1.signature == dummy2.signature and dummy1.list == dummy2.list:
print ('tDummy instances are the same')
dummy1.change_list()
if dummy1.list != dummy2.list:
print('tNow each instance is 100% independent. Deep copy goes through all nested references!')
naive_test()
shallow_copy_test()
deep_copy_test()Copyright © 2021 Codeinu
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