代码复杂请问如何理解

第二行不understand，可以拆分1下吗，或者解释也行

def decodeMorse(morse_code):
    return ' '.join(''.join(MORSE_CODE[letter] for letter in word.split(' ')) for word in morse_code.strip().split('   '))
print(decodeMorse('.... . -.--   .--- ..- -.. .'))

def decodeMorse(morse_code):
    a=''.join(MORSE_CODE[letter] for letter in word.split(' '))
    b=' '.join(a for word in morse_code.strip().split('   '))
    return b
print(decodeMorse('.... . -.--   .--- ..- -.. .'))