I'm trying to build a simple chess game in python, I've created a dictionary with positions on the pawns. I want to change dictionary into Forsyth–Edwards Notation (FEN) (the position of the pawns).
curr_position = {'a8': 'r', 'b8': 'n', 'c8': 'b', 'd8': 'q', 'e8': 'k', 'f8': 'b', 'g8': 'n', 'h8': 'r', 'a7': 'p', 'b7': 'p', 'c7': 'p', 'd7': 'p', 'e7': 'p', 'f7': 'p', 'g7': 'p', 'h7': 'p', 'a6': None, 'b6': None, 'c6': None, 'd6': None, 'e6': None, 'f6': None, 'g6': None, 'h6': None, 'a5': None, 'b5': None, 'c5': None, 'd5': None, 'e5': None, 'f5': None, 'g5': None, 'h5': None, 'a4': None, 'b4': None, 'c4': None, 'd4': None, 'e4': None, 'f4': None, 'g4': None, 'h4': None, 'a3': None, 'b3': None, 'c3': None, 'd3': None, 'e3': None, 'f3': None, 'g3': None, 'h3': None, 'a2': 'P', 'b2': 'P', 'c2': 'P', 'd2': 'P', 'e2': 'P', 'f2': 'P', 'g2': 'P', 'h2': 'P', 'a1': 'R', 'b1': 'N', 'c1': 'B', 'd1': 'Q', 'e1': 'K', 'f1': 'B', 'g1': 'N', 'h1': 'R'}
the above dictionary should return something like this in FEN:
"rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR"
I wrote
def curr_fen():
positions2 = ""
pos_temp = 0
prev_value = 0
for ix, value in enumerate(curr_position.values()):
if ix % 8 == 0 and ix != 0:
positions2 += "/"
pos_temp = 0
if not value:
pos_temp += 1
positions2 += str(pos_temp)
else:
positions2 += value
return positions2
print(curr_fen())
which returns
"nbqkbnr/pppppppp/12345678/12345678/12345678/12345678/PPPPPPPP/RNBQKBNR"
which is incorrect. How can I adjust my function to return the desired output?
As you step through the board positions you are keeping track of consecutive empty squares with pos_temp.
The number of consecutive empty squares should be added to the string whenever you find a square with a piece or you move to the next rank (if the previous rank was completely empty).
pos_temp needs to be reset to zero whenever it is added to the string.
I've made some additions and one deletion to your code.
def curr_fen():
positions2 = ""
pos_temp = 0
prev_value = 0
for ix, value in enumerate(curr_position.values()):
if ix % 8 == 0 and ix != 0:
if pos_temp > 0:
positions2 = positions2 + str(pos_temp)
positions2 += "/"
pos_temp = 0
if not value:
pos_temp += 1
# positions2 += str(pos_temp)
else:
if pos_temp > 0:
positions2 = positions2 + str(pos_temp)
pos_temp = 0
positions2 += value
return positions2
Your solution relies on the dictionary being constructed in a specific order. Here are a couple of alternatives that don't rely on the order of the original dictionary. They both have an intermediate step of transforming the original dictionary.
import collections
def f(d):
rank_order = '87654321'
file_order = 'abcdefgh'
new = collections.defaultdict(dict)
for (file,rank),piece in d.items():
new[rank].update({file:piece})
board = []
for rank in rank_order:
s = ''
temp = 0
for file in file_order:
piece = new[rank][file]
if piece is None:
temp += 1
else:
if temp > 0:
s = f'{s}{temp}'
temp = 0
s = f'{s}{piece}'
if temp > 0:
s = f'{s}{temp}'
board.append(s)
return '/'.join(board)
import itertools
def g(d):
rank_order = '87654321'
file_order = 'abcdefgh'
new1 = collections.defaultdict(list)
for (file,rank),piece in d.items():
new1[rank].append((file,piece))
board = []
for rank in rank_order:
s = ''
positions = new1[rank]
positions.sort()
for piece,items in itertools.groupby(positions,key=lambda x:x[1]):
n_pieces = len(list(items))
if piece is None:
s = f'{s}{n_pieces}'
else:
s = f'{s}{piece * n_pieces}'
board.append(s)
return '/'.join(board)