blocks|key|1986759|text|如果您所说的"array“实际上指的是Python列表，则可以使用|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1986760|a+=+[0]+*+10|code-block|syntax|javascript|1986761|或|1986762|a+=+[None]+*+10|1986763|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

If by "array" you actually mean a Python list, you can use

<pre><code>a = [0] * 10
</code></pre>

or

<pre><code>a = [None] * 10
</code></pre>

blocks|key|1986765|text|你不能在Python中做你想做的事情(如果我没看错的话)。您需要为列表中的每个元素(或您所称的数组)放入值。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1986766|但是，试试这个：|1986767|a+=+[0+for+x+in+range(N)]++#+N+=+size+of+list+you+want
a[i]+=+5++#+as+long+as+i+<+N,+you're+okay|code-block|syntax|javascript|1986768|对于其他类型的列表，请使用除0以外的值。None通常也是一个不错的选择。|offset|length|style|CODE|1986769|entityMap^0|0|0|0|K|4|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|T|8|@$K|U|L|V|M|N]]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

You can't do exactly what you want in Python (if I read you correctly). You need to put values in for each element of the list (or as you called it, array).

But, try this:

<pre><code>a = [0 for x in range(N)] # N = size of list you want
a[i] = 5 # as long as i &lt; N, you're okay
</code></pre>

For lists of other types, use something besides 0. <code>None</code> is often a good choice as well.

blocks|key|1773038|text|你也可以用list的扩展方法来扩展它。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1773039|a=+[]
a.extend([None]*10)
a.extend([None]*20)|code-block|syntax|javascript|1773040|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

also you can extend that with extend method of list.

<pre><code>a= []
a.extend([None]*10)
a.extend([None]*20)
</code></pre>

blocks|key|1773042|text|您可以使用numpy：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1773043|import+numpy+as+np|code-block|syntax|javascript|1773044|来自Empty+Array的示例|offset|length|1773045|np.empty([2,+2])
array([[+-9.74499359e%2B001,+++6.69583040e-309],
+++++++[++2.13182611e-314,+++3.06959433e-309]])++|1773046|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.scipy.org/doc/numpy/reference/generated/numpy.empty.html^0|0|0|2|B|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@]|9|@$I|X|J|Y|1|Z]]|A|$]]|$1|K|3|L|5|D|7|10|8|@]|9|@]|A|$E|F]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|T]]]]

You can use numpy:

<pre class="lang-py prettyprint-override"><code>import numpy as np
</code></pre>

Example from <a href="http://docs.scipy.org/doc/numpy/reference/generated/numpy.empty.html" rel="noreferrer">Empty Array</a>:

<pre class="lang-py prettyprint-override"><code>np.empty([2, 2])
array([[ -9.74499359e+001, 6.69583040e-309],
 [ 2.13182611e-314, 3.06959433e-309]]) 
</code></pre>

blocks|key|1773051|text|只需声明列表并附加每个元素即可。对于ex：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1773052|a+=+[]
a.append('first+item')
a.append('second+item')|code-block|syntax|javascript|1773053|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Just declare the list and append each element. For ex:

<pre><code>a = []
a.append('first item')
a.append('second item')
</code></pre>

blocks|key|1773068|text|如果您(或这个问题的其他搜索者)实际上对创建一个连续的数组来填充整数感兴趣，可以考虑使用bytearray和memoryivew|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1773069|#+cast()+is+available+starting+Python+3.3
size+=+10**6+
ints+=+memoryview(bytearray(size)).cast('i')+

ints.contiguous,+ints.itemsize,+ints.shape
#+(True,+4,+(250000,))

ints[0]
#+0

ints[0]+=+16
ints[0]
#+16|code-block|syntax|javascript|1773070|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.python.org/3/library/stdtypes.html#bytearray|1|https://docs.python.org/3/library/stdtypes.html#memoryview^0|18|9|0|1I|A|1|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@$A|T|B|U|1|V]|$A|W|B|X|1|Y]]|C|$]]|$1|D|3|E|5|F|7|Z|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|10|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]|Q|$5|L|M|N|C|$O|R]]]]

If you (or other searchers of this question) were actually interested in creating a contiguous array to fill with integers, consider <a href="https://docs.python.org/3/library/stdtypes.html#bytearray" rel="nofollow noreferrer">bytearray</a> and <a href="https://docs.python.org/3/library/stdtypes.html#memoryview" rel="nofollow noreferrer">memoryivew</a>:

<pre><code># cast() is available starting Python 3.3
size = 10**6 
ints = memoryview(bytearray(size)).cast('i') 

ints.contiguous, ints.itemsize, ints.shape
# (True, 4, (250000,))

ints[0]
# 0

ints[0] = 16
ints[0]
# 16
</code></pre>

blocks|key|1773145|text|如果你真的想要一个C风格的数组|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1773146|import+array
a+=+array.array('i',+x+*+[0])
a[3]+=+5
try:
+++[5]+=+'a'
except+TypeError:
+++print('integers+only+allowed')|code-block|syntax|javascript|1773147|请注意，python中没有未初始化变量的概念。变量是绑定到某个值的名称，因此该值必须包含某些内容。在上面的例子中，数组被初始化为零。|1773148|但是，这在python中并不常见，除非您确实需要它来处理低级内容。在大多数情况下，您最好使用空列表或空的numpy数组，正如其他答案所建议的那样。|1773149|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

If you actually want a C-style array

<pre><code>import array
a = array.array('i', x * [0])
a[3] = 5
try:
 [5] = 'a'
except TypeError:
 print('integers only allowed')
</code></pre>

Note that there's no concept of un-initialized variable in python. A variable is a name that is bound to a value, so that value must have something. In the example above the array is initialized with zeros.

However, this is uncommon in python, unless you actually need it for low-level stuff. In most cases, you are better-off using an empty list or empty numpy array, as other answers suggest.

blocks|key|1773164|text|x=[]
for+i+in+range(0,5):
++++x.append(i)
++++print(x[i])|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1773165|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>x=[]
for i in range(0,5):
 x.append(i)
 print(x[i])
</code></pre>

blocks|key|1773177|text|也可以创建具有特定大小的空数组：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1773178|array+=+[[]+for+_+in+range(n)]+#+n+equal+to+your+desired+size
array[0].append(5)+#+it+appends+5+to+an+empty+list,+then+array[0]+is+[5]|code-block|syntax|javascript|1773179|如果您将其定义为array+=+[]+*+n，那么如果您修改一项，所有项都将以相同的方式进行更改，因为它是可变的。|offset|length|style|CODE|1773180|entityMap^0|0|0|8|E|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

It is also possible to create an empty array with a certain size:
<pre><code>array = [[] for _ in range(n)] # n equal to your desired size
array[0].append(5) # it appends 5 to an empty list, then array[0] is [5]
</code></pre>
if you define it as <code>array = [] * n</code> then if you modify one item, all are changed the same way, because of its mutability.

I basically want a python equivalent of this in C:

<pre><code>int a[x];
</code></pre>

but in python I declare an array like:

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

and the problem is I want to assign random slots with values like:

<pre><code>a[4] = 1
</code></pre>

but I can't do that with python, since the array is empty.

How do I get an empty array of any size in python?

Python

我基本上想要一个python在C中的等价物：int a[x];但在python中，我声明了一个数组，如下所示：a = []问题是我想用如下的值来分配随机槽：a[4] = 1但是我不能用python做到这一点，因为数组是空的。

问如何在python中获得任意大小的空数组？
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