a=[1,2,3]
b=[4,5,6]
c=[]
d=[]
这两个声明有什么区别?a [:] = b和a = b之间的区别是什么?
c[:]=a
d=b[:]
但是两者都给出相同的结果。
c为[1,2,3],d为[4,5,6]
而没有任何区别的功能明智?
a=[1,2,3]
b=[4,5,6]
c=[]
d=[]
这两个声明有什么区别?a [:] = b和a = b之间的区别是什么?
c[:]=a
d=b[:]
但是两者都给出相同的结果。
c为[1,2,3],d为[4,5,6]
而没有任何区别的功能明智?
c[:] = a
它意味着替换C的所有元件由一个
>>> 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[:]
装置元件创建的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]]
没有太大的区别。 c[:]=a
更新c
提到的列表。 d=b[:]
创建一个新的列表,它是b的副本(忘记您在第4行创建的旧列表)。在大多数应用程序中,除非您有其他引用数组的参考,否则不太可能会看到差异。当然,在c[:]=...
版本中,您必须已经有一个名单c
。
Ashwini说什么。 :)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)
另一路:
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])
看看会发生什么?
Ashwini's answer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
非常雄辩地说明。 (从我+1) – mgilson
+1非常简洁和明确的解释 – Levon
有什么区别功能明智吗? –