在Python中创建一个具有一定大小的空列表

如何创建一个可以容纳 10 个元素的空列表？

之后，我想在该列表中分配值。例如：

xs = list()
for i in range(0, 9):
   xs[i] = i

然而，这给出了IndexError: list assignment index out of range. Why?

编者注：

_{In Python, lists do not have a set capacity, but it is not possible to assign to elements that aren't already present. Answers here show code that creates a list with 10 "dummy" elements to replace later. However, most beginners encountering this problem really just want to build a list by adding elements to it. That should be done using the .append method, although there will often be problem-specific ways to create the list more directly. Please see Why does this iterative list-growing code give IndexError: list assignment index out of range? How can I repeatedly add elements to a list? https://stackoverflow.com/questions/5653533 for details.}

您不能分配给这样的列表xs[i] = value，除非列表已至少初始化i+1元素（因为第一个索引是 0）。相反，使用xs.append(value)将元素添加到列表末尾。 （尽管如果您使用字典而不是列表，则可以使用赋值符号。）

创建一个空列表：

>>> xs = [None] * 10
>>> xs
[None, None, None, None, None, None, None, None, None, None]

为上述列表的现有元素赋值：

>>> xs[1] = 5
>>> xs
[None, 5, None, None, None, None, None, None, None, None]

请记住，类似的事情xs[15] = 5仍然会失败，因为我们的列表只有 10 个元素。

range(x) 从 [0, 1, 2, ... x-1] 创建一个列表

# 2.X only. Use list(range(10)) in 3.X.
>>> xs = range(10)
>>> xs
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

使用函数创建列表：

>>> def display():
...     xs = []
...     for i in range(9): # This is just to tell you how to create a list.
...         xs.append(i)
...     return xs
... 
>>> print display()
[0, 1, 2, 3, 4, 5, 6, 7, 8]

列表理解（使用正方形，因为对于范围，您不需要执行所有这些操作，您只需返回range(0,9) ):

>>> def display():
...     return [x**2 for x in range(9)]
... 
>>> print display()
[0, 1, 4, 9, 16, 25, 36, 49, 64]