"""
Fill in the gaps in the initials function so that it returns the initials of the words contained in the phrase received, in upper case. For example:
"Universal Serial Bus" should return "USB"; "local area network" should return "LAN”
"""


def initials(phrase):
    words = phrase.split(' ')
    result = ""
    for word in words:
        result += word[0]
    return result.upper()

print(initials("Universal Serial Bus")) # Should be: USB
print(initials("local area network")) # Should be: LAN
print(initials("Operating system")) # Should be: OS