a=[1,2,3]
b=[4,5,6]
c=[]
d=[]
请告诉我这两个语句之间的区别？
c[:]=a
d=b[:]
但两者的结果相同。
c为[1,2,3]和d是[4,5,6]
而有什么不同的功能是否明智？
Answer 1:
c[:] = a它意味着通过的元件替换C中的所有元素
>>> l = [1,2,3,4,5]
>>> l[::2] = [0, 0, 0] #you can also replace only particular elements using this
>>> l
[0, 2, 0, 4, 0]
>>> k = [1,2,3,4,5]
>>> g = ['a','b','c','d']
>>> g[:2] = k[:2] # only replace first 2 elements
>>> g
[1, 2, 'c', 'd']
>>> a = [[1,2,3],[4,5,6],[7,8,9]]
>>> c[:] = a #creates a shallow copy
>>> a[0].append('foo') #changing a mutable object inside a changes it in c too
>>> a
[[1, 2, 3, 'foo'], [4, 5, 6], [7, 8, 9]]
>>> c
[[1, 2, 3, 'foo'], [4, 5, 6], [7, 8, 9]]
d = b[:]装置创建的B A 浅拷贝并将其分配给d，它类似于d = list(b)
>>> l = [1,2,3,4,5]
>>> m = [1,2,3]
>>> l = m[::-1]
>>> l
[3,2,1]
>>> l = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
>>> m = l[:] #creates a shallow copy
>>> l[0].pop(1) # a mutable object inside l is changed, it affects both l and m
2
>>> l
[[1, 3], [4, 5, 6], [7, 8, 9]]
>>> m
[[1, 3], [4, 5, 6], [7, 8, 9]]
Answer 2:
什么阿什维尼说。 :)我会详细说明一点点：
In [1]: a=[1,2,3]
In [2]: b = a
In [3]: c = a[:]
In [4]: b, c
Out[4]: ([1, 2, 3], [1, 2, 3])
In [5]: a is b, a is c
Out[5]: (True, False)
而另一种方式：
In [1]: a = [1,2,3]
In [2]: aold = a
In [3]: a[:] = [4,5,6]
In [4]: a, aold
Out[4]: ([4, 5, 6], [4, 5, 6])
In [5]: a = [7,8,9]
In [6]: a, aold
Out[6]: ([7, 8, 9], [4, 5, 6])
走着瞧吧？
Answer 3:
没有太大的区别。 c[:]=a更新列表c是指在适当位置。 d=b[:]创建一个新的列表，它是B的复印件（忘记你4号线创建的旧列表）。 在大多数应用中，你不可能看到区别，除非你有到阵列围坐其他引用。 当然，与c[:]=...版本，你必须有一个列表c围坐了。
Answer 4:
阿什维尼的答案准确地描述发生了什么，这里有两个方法之间的差异的几个例子：
a=[1,2,3]
b=[4,5,6]
c=[]
c2=c
d=[]
d2=d
c[:]=a # replace all the elements of c by elements of a
assert c2 is c # c and c2 should still be the same list
c2.append(4) # modifying c2 will also modify c
assert c == c2 == [1,2,3,4]
assert c is not a # c and a are not the same list
d=b[:] # create a copy of b and assign it to d
assert d2 is not d # d and d2 are no longer the same list
assert d == [4,5,6] and d2 == [] # d2 is still an empty list
assert d is not b # d and b are not the same list
文章来源: What is the difference between a[:]=b and a=b[:]
