创建空列表列表 [英] Creating a List of Empty Lists
问题描述
Pythons内部''指针''系统肯定会给我带来一些
头疼.....当我想复制一个变量的内容时我发现
我不可能知道我是否复制了内容*或*只是
创建了一个指向原始值的新指针....
For例子我想初始化一个空列表列表....
a = [[]，[]，[]，[]，[]]
我认为必须有一个*非常简单的方法 - 在一次黑客攻击之后我发现：
a = [[] ] * 10似乎工作
然而 - 在我的程序中使用它称为奇怪的崩溃....
我最终发现（作为一个愚蠢的例子） ：
a = [[]] * 10
b = -1
而b < 10：
b + = 1
a [b] = b
打印一份
制作：
[[9]，[9]，[9] ......
这根本不是我想要的...... .......
这样做的正确，快捷的方法是什么（不使用循环和
追加......） ？
Fuzzyman
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mi*****@foord.net （Fuzzyman）写在
news：80 ************************** @ posting.google.c om：
我最终发现（作为一个愚蠢的例子）：
a = [[]] * 10
b = -1
而b< 10：
b + = 1
a [b] = b
打印一份
制作：
[[9]，[9]，[ 9] ......
这根本不是我想要的...............
什么是正确的，快速做到这一点（不使用循环和
附加...）？
这些天的推荐方式通常是：
a = [[] for i in range（10）]
它仍然有一个循环并通过附加空列表来工作，但至少它的
只是一个表达式。此外，您可以很容易地将
初始化的下一阶段纳入其中：
a = [[b]对于范围内的b（10）]
-
Duncan Booth du****@rcp.co。英国
int month（char * p）{return（124864 /（（p [0] + p [1] -p [2]& 0x1f）+1）％12 ）[" \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ 4"];} //谁说我的代码模糊不清？
Fuzzyman写道：Pythons内部''指针''系统肯定是引起我几个头疼.....当我想复制一个变量的内容时我发现
我不可能知道我是否复制了内容*或*只是
创建了一个指向原始值的新指针....
例如，我想初始化一个空列表列表....
a = [[]，[ ]，[]，[]，[]]
[。 ..]正确，快速的方法是什么（不使用循环和
附加......）？
< blockquote class =post_quotes>l = [[] for x in xrange（3）]
l
[[]，[]，[]] l [0 ] .append（''''）
l
[['''']，[]，[]]
Daniel
mi ***** @ foord.net （Fuzzyman）写道：
蟒蛇内部''指针''系统肯定会让我产生一些
头疼.....当我想复制变量的内容时，我发现
无法知道我是否已复制内容*或*只是
创建了一个指向原始值的新指针....
例如我想初始化一个空列表列表....
a = [[]，[]，[]，[]， []]
我认为必须有一个*真的*简单的方法 - 在一次黑客攻击之后我发现：
a = [[]] * 10似乎工作了
然而 - 在我的程序中使用它叫做奇怪的崩溃....
我最终发现（作为一个愚蠢的例子）：
a = [[]] * 10
b = -1
而b< 10：
b + = 1
a [b] = b
打印一份
制作：
[[9]，[9]，[ 9] ......
这根本不是我想要的...............
什么是正确的，这样做的快捷方式（不使用循环和
附加......）？
这里产生了一个IndexError。在改变b< 10 QUOT;进入b< 9
代码制作：
[0,1,2,3,4,5,6,7,8,9]
我看到其他一些海报已经给你答案了。我会做一些不同的事情，给你一个问题:-)
n = 4
agent = [[] ] * n
打印代理商
代理商[0] .append（''史密斯''）
打印代理商
neos = map（list，[[]] * n）
print neos
neos [0] .append（''Neo''）
打印neos
输出为：
[[]，[]，[]，[]]
[[''史密斯'']，[''史密斯''，[''史密斯'']，[''史密斯'']
[[]，[ ]，[]，[]]
[[''Neo'']，[]，[]，[]]
问题是：
为什么史密斯？复制到矩阵中的所有元素？
（或者是另一部电影:-)
Anton
Pythons internal ''pointers'' system is certainly causing me a few
headaches..... When I want to copy the contents of a variable I find
it impossible to know whether I''ve copied the contents *or* just
created a new pointer to the original value....
For example I wanted to initialize a list of empty lists....
a=[ [], [], [], [], [] ]
I thought there has to be a *really* easy way of doing it - after a
bit of hacking I discovered that :
a = [[]]*10 appeared to work
however - using it in my program called bizarre crashes....
I eventually discovered that (as a silly example) :
a = [[]]*10
b=-1
while b < 10:
b += 1
a[b] = b
print a
Produced :
[ [9], [9], [9]......
Which isn''t at all what I intended...............
What is the correct, quick way of doing this (without using a loop and
appending...) ?
Fuzzyman
http://www.Voidspace.org.uk
The Place where headspace meets cyberspace. Online resource site -
covering science, technology, computing, cyberpunk, psychology,
spirituality, fiction and more.
---
http://www.atlantibots.org.uk
http://groups.yahoo.com/group/atlantis_talk/
Atlantibots - stomping across the worlds of Atlantis.
---
http://www.fuchsiashockz.co.uk
http://groups.yahoo.com/group/void-shockz
---
Everyone has talent. What is rare is the courage to follow talent
to the dark place where it leads. -Erica Jong
Ambition is a poor excuse for not having sense enough to be lazy.
-Milan Kundera
mi*****@foord.net (Fuzzyman) wrote in
news:80**************************@posting.google.c om:
I eventually discovered that (as a silly example) :
a = [[]]*10
b=-1
while b < 10:
b += 1
a[b] = b
print a
Produced :
[ [9], [9], [9]......
Which isn''t at all what I intended...............
What is the correct, quick way of doing this (without using a loop and
appending...) ?
The recommended way these days is usually:
a = [ [] for i in range(10) ]
That still has a loop and works by appending empty lists, but at least its
just a single expression. Also you can incorporate the next stage of your
initialisation quite easily:
a = [ [b] for b in range(10) ]
--
Duncan Booth du****@rcp.co.uk
int month(char *p){return(124864/((p[0]+p[1]-p[2]&0x1f)+1)%12)["\5\x8\3"
"\6\7\xb\1\x9\xa\2\0\4"];} // Who said my code was obscure?
Fuzzyman wrote:Pythons internal ''pointers'' system is certainly causing me a few
headaches..... When I want to copy the contents of a variable I find
it impossible to know whether I''ve copied the contents *or* just
created a new pointer to the original value....
For example I wanted to initialize a list of empty lists....
a=[ [], [], [], [], [] ] [...] What is the correct, quick way of doing this (without using a loop and
appending...) ?
l = [ [] for i in xrange (3)]
l [[], [], []] l [0].append (''a'')
l
[[''a''], [], []]
Daniel
mi*****@foord.net (Fuzzyman) wrote:
Pythons internal ''pointers'' system is certainly causing me a few
headaches..... When I want to copy the contents of a variable I find
it impossible to know whether I''ve copied the contents *or* just
created a new pointer to the original value....
For example I wanted to initialize a list of empty lists....
a=[ [], [], [], [], [] ]
I thought there has to be a *really* easy way of doing it - after a
bit of hacking I discovered that :
a = [[]]*10 appeared to work
however - using it in my program called bizarre crashes....
I eventually discovered that (as a silly example) :
a = [[]]*10
b=-1
while b < 10:
b += 1
a[b] = b
print a
Produced :
[ [9], [9], [9]......
Which isn''t at all what I intended...............
What is the correct, quick way of doing this (without using a loop and
appending...) ?
Here it produced an IndexError. After changing "b < 10" into "b < 9"
the code produced:
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
I see some other posters already gave you the answer. I''ll do
something different and give you the question :-)
n = 4
agents = [[]]*n
print agents
agents[0].append(''Smith'')
print agents
neos = map(list,[[]]*n)
print neos
neos[0].append(''Neo'')
print neos
output is:
[[], [], [], []]
[[''Smith''], [''Smith''], [''Smith''], [''Smith'']]
[[], [], [], []]
[[''Neo''], [], [], []]
The question is:
Why is "Smith" copied to all elements in the matrix?
(or is that another movie :-)
Anton
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