为什么我不能使用循环在列表中创建列表？

Question

I have this code (For the left wall of roomMap):

roomMap = []
ones = [1] * 50
for i in ones:
    roomMap = roomMap + [[i]]
    roomMap.append("\n")
print(len(roomMap))
print(roomMap)

It is supposed to print 50 then [1] on 50 lines, but it prints 100 then repeats [1], '\n' 50 times.
Why is this happenning?

Answer 1

It prints 100 and repeats [1], '\n' 50 times because you append the "\n" to the roomMap.

What you did is appending both [1] and "\n" into the list "roomMap". So, for every single iteration, you are pushing 2 elements ([1] and "\n") to the list. A list is not a string, so you do not need to append the whitespace character.

Answer 2

Try using:

roomMap = []
ones = [1] * 50
for i in ones:
    roomMap = roomMap + [[i]]
print(len(roomMap))
for i in roomMap:
    print(i)

Answer 3

Here you go:

roomMap = [1] * 50 # Here, the list is filled with 1
print(len(roomMap))
for i in roomMap:
    print(i)

print() already go to next line. This print:

50
1
1
1
1 #etc..

If you want a list of lists, just add brackets

roomMap = [[1]] * 50 #Here, the list is filled with [1]
print(len(roomMap))
for i in roomMap:
    print(i)

This print

50
[1]
[1]
[1] #etc..

Answer 4

try this

roommap=[]
a=[[1]]*50
for i in a:
    roommap.append(i)
print(len(a))
print(*roommap,sep='\n')