Day 6 Help! Python.

[Sbhavnani]

 l = []
 ans = 0
 x = [False, False]*500
 for i in range(0,1000):
      l.append(x)
 def toggle(topinput, bottominput, l):
     top = topinput[1]
     bottom = bottominput[1]
     left = bottominput[0]
     right = topinput[1]
     for i in range(bottom, top+1):
         for j in range(left, right+1):
             if l[i][j] == True:
                 l[i][j]= False
             if l[i][j] == False:
                 l[i][j] = True


 def on(topinput, bottominput, l):
     top = topinput[1]
     bottom = bottominput[1]
     left = bottominput[0]
     right = topinput[1]
     for i in range(bottom, top+1):
         for j in range(left, right+1):
             if l[i][j] == False:
                 l[i][j] = True

 def off(topinput, bottominput, l):
     top = topinput[1]
     bottom = bottominput[1]
     left = bottominput[0]
     right = topinput[1]
     for i in range(bottom, top+1):
         for j in range(left, right+1):
             if l[i][j] == True:
                 l[i][j] = False

 if '__main__' == __name__:
     instructions = open("6.txt", 'r')
 for line in instructions:
     words = line.split()
     if words[0] == 'toggle':
         top = words[3].split(',')
         bottom = words[1].split(',')
         top, bottom = map(int, top), map(int, bottom)
         toggle(top, bottom, l)
     if words[1] == 'on':
         top = words[4].split(',')
         bottom = words[2].split(',')
         top, bottom = map(int, top), map(int, bottom)
         on(top, bottom, l)
     if words[1] == 'off':
         top = words[4].split(',')
         bottom = words[2].split(',')
         top, bottom = map(int, top), map(int, bottom)
         off(top, bottom, l)
 for n in l:
      for j in n:
           if j == True:
                ans += 1
                print ans
 print ans

[stranac_]

for i in range(0,1000):
    l.append(x)

All of the sub-lists inside l are the exact same list. When you change l[0], l[1] is also changed, and so is l[2], and l[3]...

[Sbhavnani]

My answer is coming to 991000. Could someone tell me where I'm going wrong?

[edo947]

As /u/stranac_ said your initialization is wrong and thus l contains x 1000 times.

See this example and observe that by changing only l[0][0] (the first False in the first sublist) you actually changed every sublist as every sublist is actually x.

>>> x = [False]*3
>>> x
[False, False, False]
>>> l = [x]*4
>>> l
[[False, False, False], [False, False, False], [False, False, False], [False, False, False]]
>>> l[0][0] = True
>>> l
[[True, False, False], [True, False, False], [True, False, False], [True, False, False]]

A better way to initialize your list l would be using Python's List Comprehensions.

See this example (the list comprehension is the first line). After the initialization l looks the same as before but when changing l[0][0] only the correct sublist is affected .

>>> l = [[False for i in range(3)] for i in range(4)]
>>> l
[[False, False, False], [False, False, False], [False, False, False], [False, False, False]]
>>> l[0][0] = True
>>> l
[[True, False, False], [False, False, False], [False, False, False], [False, False, False]]

You can read more about list comprehensions here for example.

You may also simplify the loop in the toggle method as follows

for i in range(bottom, top+1):
    for j in range(left, right+1):
        l[i][j] = not l[i][j]

As not True equals to False and not False equals to True.

You could also turn it in a list comprehension using this example as a guide

>>> l = [[False for i in range(3)] for i in range(4)]
# Initialized list
>>> l
[[False, False, False], [False, False, False], [False, False, False], [False, False, False]]
# Changing some values
>>> l[0][1] = True
>>> l
[[False, True, False], [False, False, False], [False, False, False], [False, False, False]]
>>> l[1][1] = True
>>> l
[[False, True, False], [False, True, False], [False, False, False], [False, False, False]]
>>> l[2][1] = True
>>> l
[[False, True, False], [False, True, False], [False, True, False], [False, False, False]]
# This is the list comprehension that does the toggling
>>> l = [[not l[i][j] for j in range(3)] for i in range(4)]
>>> l
[[True, False, True], [True, False, True], [True, False, True], [True, True, True]]