我想知道我如何可以初始化一个数组(或列表)，尚未与值填充，有一个定义的大小。
例如在C语言中:
int x[5]; /* declared without adding elements*/
在Python中如何做到这一点?
当前回答
您可以尝试使用Descriptor来限制大小
class fixedSizeArray(object):
def __init__(self, arraySize=5):
self.arraySize = arraySize
self.array = [None] * self.arraySize
def __repr__(self):
return str(self.array)
def __get__(self, instance, owner):
return self.array
def append(self, index=None, value=None):
print "Append Operation cannot be performed on fixed size array"
return
def insert(self, index=None, value=None):
if not index and index - 1 not in xrange(self.arraySize):
print 'invalid Index or Array Size Exceeded'
return
try:
self.array[index] = value
except:
print 'This is Fixed Size Array: Please Use the available Indices'
arr = fixedSizeArray(5)
print arr
arr.append(100)
print arr
arr.insert(1, 200)
print arr
arr.insert(5, 300)
print arr
输出:
[None, None, None, None, None]
Append Operation cannot be performed on fixed size array
[None, None, None, None, None]
[None, 200, None, None, None]
This is Fixed Size Array: Please Use the available Indices
[None, 200, None, None, None]
其他回答
最好的办法是使用numpy库。
from numpy import ndarray
a = ndarray((5,),int)
你可以使用:
>>> lst = [None] * 5
>>> lst
[None, None, None, None, None]
我想通过发布一个示例程序及其输出来帮助你
计划:
t = input("")
x = [None]*t
y = [[None]*t]*t
for i in range(1, t+1):
x[i-1] = i;
for j in range(1, t+1):
y[i-1][j-1] = j;
print x
print y
输出:
2
[1, 2]
[[1, 2], [1, 2]]
我希望这澄清了你对他们的宣言的一些非常基本的概念。 用其他特定的值初始化它们，比如用0..你可以将它们声明为:
x = [0]*10
希望能有所帮助!!；）
>>> n = 5 #length of list
>>> list = [None] * n #populate list, length n with n entries "None"
>>> print(list)
[None, None, None, None, None]
>>> list.append(1) #append 1 to right side of list
>>> list = list[-n:] #redefine list as the last n elements of list
>>> print(list)
[None, None, None, None, 1]
>>> list.append(1) #append 1 to right side of list
>>> list = list[-n:] #redefine list as the last n elements of list
>>> print(list)
[None, None, None, 1, 1]
>>> list.append(1) #append 1 to right side of list
>>> list = list[-n:] #redefine list as the last n elements of list
>>> print(list)
[None, None, 1, 1, 1]
或者一开始就什么都没有:
>>> n = 5 #length of list
>>> list = [] # create list
>>> print(list)
[]
>>> list.append(1) #append 1 to right side of list
>>> list = list[-n:] #redefine list as the last n elements of list
>>> print(list)
[1]
在append的第4次迭代中:
>>> list.append(1) #append 1 to right side of list
>>> list = list[-n:] #redefine list as the last n elements of list
>>> print(list)
[1,1,1,1]
5及所有后续:
>>> list.append(1) #append 1 to right side of list
>>> list = list[-n:] #redefine list as the last n elements of list
>>> print(list)
[1,1,1,1,1]
您可以尝试使用Descriptor来限制大小
class fixedSizeArray(object):
def __init__(self, arraySize=5):
self.arraySize = arraySize
self.array = [None] * self.arraySize
def __repr__(self):
return str(self.array)
def __get__(self, instance, owner):
return self.array
def append(self, index=None, value=None):
print "Append Operation cannot be performed on fixed size array"
return
def insert(self, index=None, value=None):
if not index and index - 1 not in xrange(self.arraySize):
print 'invalid Index or Array Size Exceeded'
return
try:
self.array[index] = value
except:
print 'This is Fixed Size Array: Please Use the available Indices'
arr = fixedSizeArray(5)
print arr
arr.append(100)
print arr
arr.insert(1, 200)
print arr
arr.insert(5, 300)
print arr
输出:
[None, None, None, None, None]
Append Operation cannot be performed on fixed size array
[None, None, None, None, None]
[None, 200, None, None, None]
This is Fixed Size Array: Please Use the available Indices
[None, 200, None, None, None]
