我开始使用python,我尝试使用一个二维列表,我开始在每个地方都用相同的变量填充。我想到了这个:

def initialize_twodlist(foo):
    twod_list = []
    new = []
    for i in range (0, 10):
        for j in range (0, 10):
            new.append(foo)
        twod_list.append(new)
        new = []

它给出了预期的结果,但感觉像是一种变通方法。有更简单/更短/更优雅的方法吗?


当前回答

添加维度的一般模式可以从这个系列中得出:

x = 0
mat1 = []
for i in range(3):
    mat1.append(x)
    x+=1
print(mat1)


x=0
mat2 = []
for i in range(3):
    tmp = []
    for j in range(4):
        tmp.append(x)
        x+=1
    mat2.append(tmp)

print(mat2)


x=0
mat3 = []
for i in range(3):
    tmp = []
    for j in range(4):
        tmp2 = []
        for k in range(5):
            tmp2.append(x)
            x+=1
        tmp.append(tmp2)
    mat3.append(tmp)

print(mat3)

其他回答

Python中经常出现的一个模式是

bar = []
for item in some_iterable:
    bar.append(SOME EXPRESSION)

这有助于推动列表推导式的引入,它将代码片段转换为

bar = [SOME_EXPRESSION for item in some_iterable]

这样更简短,有时也更清楚。通常,您会养成识别这些循环的习惯,并经常用推导式替换循环。

您的代码遵循此模式两次

twod_list = []                                       \                      
for i in range (0, 10):                               \
    new = []                  \ can be replaced        } this too
    for j in range (0, 10):    } with a list          /
        new.append(foo)       / comprehension        /
    twod_list.append(new)                           /

正如@Arnab和@Mike指出的,数组不是列表。不同之处在于:1)数组在初始化时是固定大小的;2)数组通常支持比列表更少的操作。

也许在大多数情况下有点多余,但这里有一个基本的2d数组实现,它利用python ctypes(c库)实现硬件数组。

import ctypes
class Array:
    def __init__(self,size,foo): #foo is the initial value
        self._size = size
        ArrayType = ctypes.py_object * size
        self._array = ArrayType()
        for i in range(size):
            self._array[i] = foo
    def __getitem__(self,index):
        return self._array[index]
    def __setitem__(self,index,value):
        self._array[index] = value
    def __len__(self):
        return self._size

class TwoDArray:
    def __init__(self,columns,rows,foo):
        self._2dArray = Array(rows,foo)
        for i in range(rows):
            self._2dArray[i] = Array(columns,foo)

    def numRows(self):
        return len(self._2dArray)
    def numCols(self):
        return len((self._2dArray)[0])
    def __getitem__(self,indexTuple):
        row = indexTuple[0]
        col = indexTuple[1]
        assert row >= 0 and row < self.numRows() \
               and col >=0 and col < self.numCols(),\
               "Array script out of range"
        return ((self._2dArray)[row])[col]

if(__name__ == "__main__"):
    twodArray = TwoDArray(4,5,5)#sample input
    print(twodArray[2,3])

用最简单的思路来创建这个。

wtod_list = []

并添加尺寸:

wtod_list = [[0 for x in xrange(10)] for x in xrange(10)]

或者如果我们想先声明大小。我们只使用:

   wtod_list = [[0 for x in xrange(10)] for x in xrange(10)]

你可以使用列表推导式:

x = [[foo for i in range(10)] for j in range(10)]
# x is now a 10x10 array of 'foo' (which can depend on i and j if you want)

初始化一个大小为m X n的二维矩阵,取值为0

m,n = map(int,input().split())
l = [[0 for i in range(m)] for j in range(n)]
print(l)