Functional solution to https://adventofcode.com/2016/day/1 part 1 with reduce() and lambda vs no lambda

d1p1.py

#!/usr/bin/env python3

# Functional solution to https://adventofcode.com/2016/day/1 part 1
# with reduce() and lambda vs no lambda
# Mark Jenkins <mark@markjenkins.ca>

from functools import reduce

MOVEMENTS = ((0,1), (1,0), (0,-1), (-1,0))
DIRECTION_CHANGES = {"R": 1, "L": -1}
def next_pos(state, token):
    displacement, direction = state
    change_dir = DIRECTION_CHANGES[token[0]]
    change_magnitude = int(token[1:])
    new_direction = (direction + change_dir) % len(MOVEMENTS)
    move = (change_magnitude*MOVEMENTS[new_direction][0], 
            change_magnitude*MOVEMENTS[new_direction][1] )
    new_displacement = (displacement[0] + move[0], displacement[1] + move[1])
    return new_displacement, new_direction

# commented out to avoid running twice
# displacement, direction = reduce( 
#     next_pos,
#     input().split(", "),
#     ((0, 0), 0) 
# ) # reduce

# print( displacement )
# print( abs(displacement[0]) + abs(displacement[1]) )

# alternative way to write the above, 
# some harder to read character code golf version with mandatory lambda
M = ((0,1), (1,0), (0,-1), (-1,0))
D = {"R": 1, "L": -1}
d, i = reduce( 
    lambda s,t: ( 
        ( s[0][0] + int(t[1:])*M[(s[1]+D[t[0]]) % len(M)][0],
          s[0][1] + int(t[1:])*M[(s[1]+D[t[0]]) % len(M)][1],
          ),
        (s[1]+D[t[0]]) % len(M)
    ),
    input().split(", "),
    ((0, 0), 0) 
)

# looks a little better in python 2 before PEP 3113 came along,
# but you can also take this as an argument against using lambda
# in the first place
# https://www.python.org/dev/peps/pep-3113/
# d, i = reduce( 
#     lambda (p,d),t: ( 
#         ( p[0] + int(t[1:])*M[(d+D[t[0]]) % len(M)][0],
#           p[1] + int(t[1:])*M[(d+D[t[0]]) % len(M)][1],
#           ),
#         (d+D[t[0]]) % len(M)
#     ),
#     raw_input().split(", "),
#     ((0, 0), 0) 
# )

#print(d)
print( abs(d[0]) + abs(d[1]) )