问题：如何在python中获取任何大小的空数组？
我基本上想在C语言中使用python等效：
int a[x];
但在python中，我声明了一个数组，如：
a = []
问题是我想给随机槽分配值，例如：
a[4] = 1
但由于数组为空，我无法使用python做到这一点。
I basically want a python equivalent of this in C:
int a[x];
but in python I declare an array like:
a = []
and the problem is I want to assign random slots with values like:
a[4] = 1
but I can’t do that with python, since the array is empty.
回答 0
如果按“数组”实际上是指Python列表，则可以使用
a = [0] * 10
要么
a = [None] * 10
If by “array” you actually mean a Python list, you can use
a = [0] * 10
or
a = [None] * 10
回答 1
您不能完全按照Python的要求进行操作（如果我没看错的话）。您需要为列表的每个元素（或您所说的数组）放入值。
但是，请尝试以下操作：
a = [0 for x in range(N)] # N = size of list you want
a[i] = 5 # as long as i < N, you're okay
对于其他类型的列表，也可以使用0以外的 None值。
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:
a = [0 for x in range(N)] # N = size of list you want
a[i] = 5 # as long as i < N, you're okay
For lists of other types, use something besides 0. None is often a good choice as well.
回答 2
您可以使用numpy：
import numpy as np
来自空数组的示例：
np.empty([2, 2])
array([[ -9.74499359e+001, 6.69583040e-309],
[ 2.13182611e-314, 3.06959433e-309]])
You can use numpy:
import numpy as np
Example from Empty Array:
np.empty([2, 2])
array([[ -9.74499359e+001, 6.69583040e-309],
[ 2.13182611e-314, 3.06959433e-309]])
回答 3
只需声明列表并附加每个元素即可。例如：
a = []
a.append('first item')
a.append('second item')
Just declare the list and append each element. For ex:
a = []
a.append('first item')
a.append('second item')
回答 4
您也可以使用list的extend方法扩展它。
a= []
a.extend([None]*10)
a.extend([None]*20)
also you can extend that with extend method of list.
a= []
a.extend([None]*10)
a.extend([None]*20)
回答 5
如果您（或该问题的其他搜索者）实际上对创建一个用整数填充的连续数组感兴趣，请考虑bytearray和memoryivew：
# 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
If you (or other searchers of this question) were actually interested in creating a contiguous array to fill with integers, consider bytearray and memoryivew:
# 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
回答 6
x=[]
for i in range(0,5):
x.append(i)
print(x[i])
x=[]
for i in range(0,5):
x.append(i)
print(x[i])
回答 7
如果您确实想要C样式的数组
import array
a = array.array('i', x * [0])
a[3] = 5
try:
[5] = 'a'
except TypeError:
print('integers only allowed')
请注意，python中没有未初始化变量的概念。变量是绑定到值的名称，因此该值必须具有某些内容。在上面的示例中，数组以零初始化。
但是，这在python中并不常见，除非您实际上需要低级的东西。在大多数情况下，如其他答案所示，使用空列表或空numpy数组会更好。
If you actually want a C-style array
import array
a = array.array('i', x * [0])
a[3] = 5
try:
[5] = 'a'
except TypeError:
print('integers only allowed')
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.
