#1.copy模組

方法:
（1）copy.copy(x)
Return a shallow copy of x.
（2）copy.deepcopy(x)
Return a deep copy of x.
（3）exception copy.error
Raised for module specific errors.

#2.shallow copy 和deep copy

The difference between shallow and deep copying is only relevant for compound objects (objects that contain other objects, like lists or class instances):
•A shallow copy constructs a new compound object and then (to the extent possible) inserts references into it to the objects found in the original.
•A deep copy constructs a new compound object and then, recursively, inserts copies into it of the objects found in the original.

shallow copy只是複製物件的引用，並不複製物件本身；而deep copy完全複製一份原始檔（深淺拷貝的區別只適用於混合物件的拷貝）

深拷貝存在的問題：Two problems often exist with deep copy operations that don’t exist with shallow copy operations:
•Recursive objects (compound objects that, directly or indirectly, contain a reference to themselves) may cause a recursive loop.
•Because deep copy copies everything it may copy too much, such as data which is intended to be shared between copies.
解決方案：
The deepcopy() function avoids these problems by:
•keeping a “memo” dictionary of objects already copied during the current copying pass; and
•letting user-defined classes override the copying operation or the set of components copied.

下例：淺拷貝

a=[1,2,3,[4,5,6],7,8]
b=a.copy()
c=a
a[1]='sb'
a[3][1]='shit'
print(a, b, c, sep='\n')
#result
[1, 'sb', 3, [4, 'shit', 6], 7, 8]
[1, 2, 3, [4, 'shit', 6], 7, 8]
[1, 'sb', 3, [4, 'shit',6], 7, 8]