Discussion on: Advent of Code 2020 Solution Megathread - Day 4: Passport Processing

[Yuan Gao]

I went ahead and wrote a solution using PEG in Python (parsimonious library). Aside from the slightly compact PEG grammar, the rest of it is very readable

from parsimonious.grammar import Grammar, NodeVisitor
from parsimonious.exceptions import ParseError, IncompleteParseError, VisitationError

grammar = Grammar(r"""
    EXPR  = ITEM+
    ITEM  = (BYR / IYR / EYR / HGT / HCL / ECL / PID / CID) WHITE?
    WHITE =  ~r"[\s]+"

    BYR   = "byr:" NUMB
    IYR   = "iyr:" NUMB
    EYR   = "eyr:" NUMB
    HGT   = "hgt:" (HGTCM / HGTIN)
    HCL   = "hcl:" ~r"#[0-9a-f]{6}"
    ECL   = "ecl:" ("amb" / "blu" / "brn" / "gry" / "grn" / "hzl" / "oth") 
    PID   = "pid:" ~r"[0-9]{9}"
    CID   = "cid:" ~r"[0-9a-zA-Z]*"

    HGTCM = NUMB "cm"
    HGTIN = NUMB "in"

    NUMB  = ~r"[0-9]{2,4}"
""")

class PassportVisitor(NodeVisitor):
    def visit_EXPR(self, node, visited_children):
        assert not {"BYR", "IYR", "EYR", "HGT", "HCL", "ECL", "PID"}.difference(visited_children)

    def visit_ITEM(self, node, visited_children):
        return node.children[0].children[0].expr_name

    def visit_BYR(self, node, visited_children):
        assert 1920 <= visited_children[1] <= 2002

    def visit_IYR(self, node, visited_children):
        assert 2010 <= visited_children[1] <= 2020

    def visit_EYR(self, node, visited_children):
        assert 2020 <= visited_children[1] <= 2030

    def visit_HGTCM(self, node, visited_children):
        assert 150 <= visited_children[0] <= 193

    def visit_HGTIN(self, node, visited_children):
        assert 59 <= visited_children[0] <= 76

    def visit_NUMB(self, node, visited_children):
        return int(node.text)

    def generic_visit(self, node, visited_children):
        return visited_children or node

pv = PassportVisitor()
pv.grammar = grammar

data = open("input.txt").read().split("\n\n")
valid = 0
for entry in data:
    try:
        pv.parse(entry)
    except (ParseError, VisitationError, IncompleteParseError):
        continue
    else:
        valid += 1
print("Valid:", valid)