带有列表的python嵌套循环

Question

ok So I am practiving a couple problems and have no idea how to start this one. I do not understand really well how to do nested loops, so we are given a list that creates a smiley face, and then this instructions.

smiley = [[" ","#"," ","#"," "],
      [" ","#"," ","#"," "],
      [" ","#"," ","#"," "],
      [" "," "," "," "," "],
      ["#"," "," "," ","#"],
      [" ","#"," ","#"," "],
      [" ","#","#","#"," "],
      [" "," "," "," "," "]]

Create a new local variable based on smiley defined above. More strictly, your definition of this new variable needs to explicitly use the variable smiley.  Use nested for loops to change the characters stored in your newly created local variable. Do not add or remove any elements from any list. Only change/replace. You can, however, change and replace any of the characters with any other single characters.  Return this local list of lists.

so how do I do nested loops for these list and change their items without changing everything else??

I only have this but I don't think it is even how I should start, please help me

def moodSwing():
face = smiley.copy()
for each in face[:1]:
    for each in face[1:2]:

Answer 1

Try the following to switch between "#" and " " at the desired row number and character number:

def moodSwing(smiley, coords):
    face = list(smiley)
    for row, character in coords:
        for r in range(len(face)):
            for c in range(r):
                if r == row+1 and c == character+1:
                    if face[r][c] == " ":
                        face[r][c] = "#"
                    else:
                        face[r][c] = " "
    return face

Then do the following:

>>> frown = moodSwing(smiley, [(4, 0), (4, 4), (5, 1), (5, 2), (5, 3), (6, 1), (6, 2), (6, 3)])

Answer 2

for list_index, lst in enumerate(face):
    for item_index, item in enumerate(lst):
        if item == '#':
            face[list_index][item_index] = ' '
        else:
            face[list_index][item_index] = '#'  

The above code flips characters. item is an element in the current list.
Use the indices to change elements.