CODEWITHSUNDEEP
pythonpython-2.7list-comprehensionnested-lists
Lornioiz
Lornioiz

Reputation: 415

Comprehension list on nested list (list of lists)

It is allowed the use of a comprehension list on a "list of lists"? I would like to extract a list from a nested list. I did try this:

def main():
    a = ['1','2','3']
    b = ['4','5','6']
    c = ['7','8','9']
    board = [a,b,c]
    y = [x for x in board[1][i] if i in range(0,3)]
    print y

but I get "NameError: name 'i' is not defined". I'm using the wrong syntax or nested list cannot be used like this?

Thanks a lot!

Upvotes: 0

Views: 210

Answers (1)

Martijn Pieters
Martijn Pieters

Reputation: 1124788

Nesting loops in list comprehensions work the same way as nesting regular for loops, one inside the other:

y = [x for i in range(3) for x in board[1][i]]

but in this case, just selecting board[1][:] would be easier and give you the same result; a copy of the middle row.

If you need to apply an expression to each column in that row, then just loop over board[1] directly:

y = [foobar(c) for c in board[1]]

Upvotes: 2

Related Questions