Python: deepcopy does not work on user-defined classes?

问题

In the following example I would expect deepcopy to create a copy of field and not just copy the reference. What happens here and is there an easy way around it?

from copy import deepcopy

class Test:
    field = [(1,2)]

t1 = Test()
t2 = deepcopy(t1)

t2.field[0]=(5,10)

print t1.field # [(1,2)] expected but [(5,10)] obtained
print t2.field # [(5,10)] expected

Output:

[(5, 10)]
[(5, 10)]

回答1:

Deep copying (by default) only applies to instance level attributes - not class level - It doesn't make much sense that there's more than one unique class.attribute...

Change your code to:

class Test:
    def __init__(self):
        self.field = [(1,2)]

来源：https://stackoverflow.com/questions/18364284/python-deepcopy-does-not-work-on-user-defined-classes