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Write a function named passports that examines an input file full of passport data and returns the number of passports that are valid. Your function accepts a string parameter representing a file name as a parameter. A valid passport is one that contains all of the following required fields:

  • byr (Birth Year)
  • iyr (Issue Year)
  • eyr (Expiration Year)
  • hgt (Height)
  • hcl (Hair Color)
  • ecl (Eye Color)
  • pid (Passport ID)

A passport can also contain the following optional field:

  • cid (Country ID)

Each passport in the input file is represented as a sequence of key:value pairs separated by spaces or newlines. Passports are separated by blank lines. For example, if the file named passports.txt contains the following text:

ecl:gry pid:860033327 eyr:2020 hcl:#fffffd
byr:1937 iyr:2017 cid:147 hgt:183cm

iyr:2013 ecl:amb cid:350 eyr:2023 pid:028048884
hcl:#cfa07d byr:1929

hcl:#ae17e1 iyr:2013
ecl:brn pid:760753108 byr:1931

hcl:#cfa07d eyr:2025 pid:166559648
iyr:2011 ecl:brn hgt:59in

The first passport is valid all eight fields are present. The second passport is invalid it is missing hgt (the Height field). The third passport is valid it is missing only the optional cid (country ID) field. The fourth passport is invalid it is missing two fields, cid and byr. Missing cid is fine, but missing any other field such as byr is not. So the call of passports("passwords.txt") should return 2.

You may assume that the file exists and is readable and that it follows the format described above.

Function: Write a Python function as described, not a complete program.

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