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diff --git a/day4/day4.py b/day4/day4.py
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+"""Day 4 code."""
+import re
+from itertools import chain, groupby
+
+REQUIRED_FIELDS = set(["byr", "ecl", "eyr", "hcl", "hgt", "iyr", "pid"])
+EYE_COLORS = ["amb", "blu", "brn", "gry", "grn", "hzl", "oth"]
+HCL_PATTERN = r"^#([a-fA-F0-9]{6})$"
+PID_PATTERN = "^([0-9]{9})$"
+
+
+def passport_str_to_list(passport_str):
+    """Convert string of passport data into list of key, values.
+
+    The reqason we use tuple is so that when we eventually get a full list that
+    presents all of key values of passport we can convert it into a dict easier.
+    """
+    pairs = passport_str.split(" ")
+    return [tuple(x.split(":")) for x in pairs]
+
+
+def passport_parser(itr):
+    """Parse passport data into individual passports.
+
+    Groupby allows us to generate a new group every time we encounter an empty
+    line which signifies the boundary of each passport's data.
+    """
+    for k, groups in groupby(data, lambda x: x == ""):
+        if k is False:
+            yield chain.from_iterable(passport_str_to_list(x) for x in groups)
+
+
+def passport_has_required_fields(passport):
+    """Check if passport is valid."""
+    return REQUIRED_FIELDS.issubset(set(passport.keys()))
+
+
+data = map(str.strip, open("input"))
+passports = [dict(x) for x in passport_parser(data)]
+
+print("Part 1:", sum(map(passport_has_required_fields, passports)))
+
+
+def byr_is_valid(passport):
+    """Check birthyear is valid."""
+    return 1920 <= int(passport["byr"]) <= 2002
+
+
+def iyr_is_valid(passport):
+    """Check issue year is valid."""
+    return 2010 <= int(passport["iyr"]) <= 2020
+
+
+def eyr_is_valid(passport):
+    """Check expiration year is valid."""
+    return 2020 <= int(passport["eyr"]) <= 2030
+
+
+def hgt_is_valid(passport):
+    """Check the hieght is valid."""
+    hgt = passport["hgt"]
+    if "cm" in hgt:
+        val = int(hgt[: hgt.find("cm")])
+        if 150 <= val <= 193:
+            return True
+    elif "in" in hgt:
+        val = int(hgt[: hgt.find("in")])
+        if 59 <= val <= 76:
+            return True
+    return False
+
+
+def hcl_is_valid(passport):
+    """Check hair color is valid."""
+    return re.match(HCL_PATTERN, passport["hcl"])
+
+
+def ecl_is_valid(passport):
+    """Check if eye color is valid."""
+    return passport["ecl"] in EYE_COLORS
+
+
+def pid_is_valid(passport):
+    """Check passport id is valid."""
+    return re.match(PID_PATTERN, passport["pid"])
+
+
+VALIDATION_TESTS = [
+    byr_is_valid,
+    iyr_is_valid,
+    eyr_is_valid,
+    hgt_is_valid,
+    hcl_is_valid,
+    ecl_is_valid,
+    pid_is_valid,
+]
+
+
+def passport_is_valid(passport):
+    """Check if a passport is valid."""
+    return all(func(passport) for func in VALIDATION_TESTS)
+
+
+passports_with_required_fields = filter(passport_has_required_fields, passports)
+print("Answer 2", sum(map(passport_is_valid, passports_with_required_fields)))