day 4

4b.py (solves both problems, some comments removed bc they were annoying me):

# Passport data is validated in batch files (your puzzle input).
# Each passport is represented as a sequence of key:value pairs separated by spaces or newlines.
# Passports are separated by blank lines.
# need to have byr, iyr, eyr, hgt, hcl, ecl, pid
# has cid => passport
# does not have cid => north pole credentials (npc)
# ^ treat each of these two as valid
#    #    #    #    #    #    #    #
# input
with open('4.txt', 'r') as file:
    input = file.read()
input_list = list(input.split('\n\n'))
# it can be split by spaces or line breaks
# change line breaks to spaces, then split on spaces
# make these tuples where each entry is like 'eyr:2026'
# then turn these into dicts
passport_list = []
for passport_str in input_list:
    passport_tuple = passport_str.replace('\n', ' ').split(' ')
    passport_dict = {}
    for field in passport_tuple:
        key_val = field.split(':')
        passport_dict[key_val[0]] = key_val[1]
    passport_list.append(passport_dict)
#    #    #    #    #    #    #    #
needed_fields = ['byr', 'iyr', 'eyr', 'hgt', 'hcl', 'ecl', 'pid']
maybe_valid = [] # has all required fields
invalid = [] # missing a required field
for passport in passport_list:
    fields = passport.keys() # list of the fields
    # make sure set of fields contains all needed fields
    if set(needed_fields).issubset(set(fields)):
        maybe_valid.append(passport)
    else: # invalid
        invalid.append(passport)
print('first problem: ' + str(len(maybe_valid)))
#    #    #    #    #    #    #    #
# add some data validation, quick
valid = [] # satisfies all the checks
for passport in maybe_valid:
    byr = int(passport['byr'])
    if byr < 1920 or byr > 2002:
        invalid.append(passport)
        print('byr ' + str(byr))
        continue
    iyr = int(passport['iyr'])
    if iyr < 2010 or iyr > 2020:
        invalid.append(passport)
        print('iyr ' + str(iyr))
        continue
    eyr = int(passport['eyr'])
    if eyr < 2020 or eyr > 2030:
        invalid.append(passport)
        print('eyr ' + str(eyr))
        continue
    hgt = (passport['hgt'][:-2], passport['hgt'][-2:])
    # e.g. hgt = ('142', 'cm')
    # has to be in or cm, different rules for each
    # ints done later in case it doesn't end cm or in
    if hgt[1] == 'cm':
        if int(hgt[0]) < 150 or int(hgt[0]) > 193:
            invalid.append(passport)
            print('hgt ' + str(hgt))
            continue
    elif hgt[1] == 'in':
        if int(hgt[0]) < 59 or int(hgt[0]) > 76:
            invalid.append(passport)
            print('hgt ' + str(hgt))
            continue
    else: # not cm or in
        invalid.append(passport)
        print('hgt ' + str(hgt))
        continue
    hcl = passport['hcl']
    if hcl[0] == '#': # starts with #
        if len(hcl) == 7: # 6 characters after the #
            for i in range(1,7): # char by char
                # want good letter or int
                if i not in ['a', 'b', 'c', 'd', 'e', 'f']:
                    try: # try to make it an int
                        j = int(i)
                    except: # i is not an int
                        invalid.append(passport)
                        print('hcl ' + str(hcl))
                        continue
    else: # does not start with #
        invalid.append(passport)
        print('hcl ' + str(hcl))
        continue
    ecl = passport['ecl']
    if ecl not in ['amb', 'blu', 'brn', 'gry', 'grn', 'hzl', 'oth']:
        invalid.append(passport)
        print('ecl ' + str(ecl))
        continue
    pid = passport['pid']
    if len(pid) == 9: # 9 characters 
       try:  # try to make it an int
            int_pid = int(pid)
        except:  # pid is not an int
            invalid.append(passport)
            print('pid ' + str(pid))
            continue
    else:
        invalid.append(passport)
        print('pid ' + str(pid))
        continue
    # no continue => all validation checks passed
    valid.append(passport)
print('second problem: ' + str(len(valid)))

so... this one wasn't impossible, just really finicky with the data validation rules (and it took way too long to figure out that i'd accidentally missed the last 'else', so passport ids that were integers but not 9 characters long were being accepted).

the first section reads in all of these passports and converts them into dicts; this was the best way to sort out the 'key: value' pairs. the next section does the first part of the problem, which is checking whether all of the required fields are present, by checking if the list of field names is a subset of the list of keys. the third part does all of the data validation - any time one field failing the validation check is found, it adds the passport to a list of invalid passports, prints the problematic field to the console, and then goes to the next passport; if no continues are hit, then the passport is valid, so it's added to the list of valid passports.

i have no idea how to format double line breaks so i've just put a bunch of #s