Pythonic way or more comprehensible with less struggle? [closed]

Question

I am trying to be more Pythonic and less C++. However the limit of all lines to a maximum of 79 characters creates everyday struggle. Here is one example:

def list_of_possible_moves(self):  # version 1
    return [] if self._state != Game.play else [index for index, square in enumerate(self._board) if square == TicTacToe.square_free]

It is 138 characters long and has to be broken. (1) In three lines:

def list_of_possible_moves(self):  # version 2
    return [] if self._state != Game.play else\
        [index for index, square in enumerate(self._board)
         if square == TicTacToe.square_free]

(2) Possible in two lines (i, s instead index, square). Still 80, not 79:

def list_of_possible_moves(self):  # version 3
    return [] if self._state != Game.play else\
        [i for i, s in enumerate(self._board) if s == TicTacToe.square_free]

(3) In the end, I decided to keep that version:

def list_of_possible_moves(self): # version 4 (C++)
    if self._state is not Game.play:
        return []
    list_of_moves = []
    for index, square in enumerate(self._board):
        if square == TicTacToe.square_free:
            list_of_moves.append(index)
    return list_of_moves

What do I do wrong? Any better way to write this piece of code?

Answer 1

This is a style/taste question; when in doubt, use the black code formatter on your code; if it looks ugly after Black, split it into multiple statements.

I'd "split the difference" and take care of the special case first, then use a list comprehension.

def list_of_possible_moves(self):
    if self._state is not Game.play:  # Not playing, no moves possible.
        return []
    return [
        index
        for index, square in enumerate(self._board)
        if square == TicTacToe.square_free
    ]

Answer 2

First, you can expand your if, else one-liner:

def list_of_possible_moves(self):
    if self._state != Game.play:
        return []
    else:
        return [index for index, square in enumerate(self._board) if square == TicTacToe.square_free]

But it's still a bit longer. A good way to break a comprehension is value - for - condition, as suggested by the Google styleguide:

def list_of_possible_moves(self):
    if self._state != Game.play:
        return []
    else:
        return [
            index 
            for index, square in enumerate(self._board) 
            if square == TicTacToe.square_free
        ]

But if you don't want to expand it, you can rename index into i, which is perfectly valid in 1. a comprehension, and 2. with enumerate. You can rename square as well:

def list_of_possible_moves(self):
    if self._state != Game.play:
        return []
    else:
        return [i for i, sq in enumerate(self._board) if sq == TicTacToe.square_free]

Here it's 85 character long, so just a little too long, but this can help reduce your lines in general.