blocks|key|2556233|text|Python不知道ball是一个列表。在使用它之前(在第一个for循环中)，您必须将它初始化为|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2556234|ball+=+[]|code-block|syntax|javascript|2556235|所以Python知道把它当作一个列表来处理。|2556236|entityMap^0|9|4|U|3|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|U|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|N|$]]

Python doesn't know that <code>ball</code> is a list. Before using it (in the first <code>for</code> loop), you'll have to initialize it as

<pre><code>ball = []
</code></pre>

so Python knows to treat it as a list.

blocks|key|838437|text|未定义任何ball。这一行：ball[i][j]=sphere()为ball指向的对象的一个元素赋值。ball没有指向任何东西，因此不可能赋值任何东西。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|838438|entityMap^0|5|4|E|J|Y|4|1F|4|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|G|$]]

no <code>ball</code> is not defined. this line: <code>ball[i][j]=sphere()</code> assigns value to an element of object <code>ball</code> points to. There is nothing <code>ball</code> points to therefore it's not possible to assign anything.

blocks|key|840330|text|不，未定义ball。您需要先创建一个list()，然后才能开始分配给列表的索引。类似地，需要在将嵌套列表分配给它们之前创建它们。试试这个：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|840331|ball+=+[None]+*+5

for+i+in+range(5):
++++ball[i]+=+[None]+*+5

++++for+j+in+range(5):
++++++++ball[i][j]=sphere()|code-block|syntax|javascript|840332|或者这样：|840333|ball+=+[[sphere()+for+y+in+range(5)]+for+x+in+range(5)]|840334|使用两个列表理解的后一种语法更惯用--如果您愿意的话，它更像Pythonic式的语法。|840335|entityMap^0|5|4|I|6|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|Y|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|10|8|@]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|R|$]]

No, <code>ball</code> is not defined. You need to create a <code>list()</code> before you can start assigning to the list's indices. Similarly the nested lists need to be created before you assign to them. Try this:

<pre><code>ball = [None] * 5

for i in range(5):
 ball[i] = [None] * 5

 for j in range(5):
 ball[i][j]=sphere()
</code></pre>

or this:

<pre><code>ball = [[sphere() for y in range(5)] for x in range(5)]
</code></pre>

The latter syntax which uses two list comprehensions is more idiomatic--more Pythonic, if you will.

blocks|key|2556333|text|当你说ball[i][j]时，你必须已经有了一些对象ball，这样你才能索引(两次)它。请尝试此段：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2556334|ball+=+[]++++
for+i+in+range(5):
++++ball.append([])
++++for+y+in+range(5):
++++++++ball[i].append(sphere())|code-block|syntax|javascript|2556335|entityMap^0|3|A|Q|4|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

When you say <code>ball[i][j]</code>, you have to already have some object <code>ball</code> so that you can index (twice) into it. Try this segment instead:

<pre><code>ball = [] 
for i in range(5):
 ball.append([])
 for y in range(5):
 ball[i].append(sphere())
</code></pre>

blocks|key|840363|text|在您的程序中，ball只是一个不引用任何东西的名称。使用像a[i]这样的索引需要a引用一个已经支持索引的对象。类似地，a[i][j]要求a[i]引用支持索引的对象。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|840364|听起来您希望它引用一个列表列表，但这不是一个很好的解决方案。你可能会更乐意在numpy数组上执行你的操作，它可以抽象出你所有的循环，并且可以真正加快计算速度。|840365|entityMap^0|7|4|T|4|14|1|1N|7|1W|4|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]|$9|Q|A|R|B|C]|$9|S|A|T|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|U|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|I|$]]

In your program, <code>ball</code> is just a name that doesn't refer to anything. Using indexing like <code>a[i]</code> requires that <code>a</code> refer to an object that already supports indexing. Similarly, <code>a[i][j]</code> requires that <code>a[i]</code> refer to an object that supports indexing.

It sounds like you want it to refer to a list of lists, but this is not a great solution. You may be a lot happier performing your operations on numpy arrays, which abstract away all your looping and can really speed up computations.

I get this error:

<pre><code>Traceback (most recent call last):
 File "D:/Python26/PYTHON-PROGRAMME/049 bam", line 9, in &lt;module&gt;
 ball[i][j]=sphere()
NameError: name 'ball' is not defined
</code></pre>

when I run this code. But the ball is defined ( ball[i][j]=sphere() ). Isn`t it?

<pre><code>#2D-wave
#VPython

from visual import *

#ball array #ready
for i in range(5):
 for y in range(5):
 ball[i][j]=sphere()

timer = 0
dt = 0.001
while(1):
 timer += dt

 for i in range(5):
 for y in range(5):
 #wave equation
 x = sqrt(i**2 + j**2) # x = distance to the source
 ball[i][j].pos.y = amplitude * sin (k * x + omega * timer)
 if timer &gt; 5:
 break
</code></pre>

Python: ball isn't defined

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我得到了这个错误：Traceback (most recent call last): File "D:/Python26/PYTHON-PROGRAMME/049 bam", line 9, in <module> ball[i][j]=sphere()NameError: name 'ball' is no...

问Python:没有定义ball
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