我无法理解这个列表理解

Question

a = [x+y for x in ['Python ','C '] for y in ['Language','Programming']]
print(a)

the output is ['Python Language', 'Python Programming', 'C Language', 'C Programming']

I thought that two list added together should be like ['Python ','C ','Language','Programming']

Answer 1

Simply "deconstruct" the comprehension from left to right, it is the same as nesting for loops to give you the Cartesian product of the two lists:

a = []
for x in ['Python ','C ']:
    for y in ['Language','Programming']:
        a.append(x+y)
# ['Python Language', 'Python Programming', 'C Language', 'C Programming']

What you had in mind as expected output is the result of a list concatenation like

a = ['Python ','C '] + ['Language','Programming']
# ['Python ', 'C ', 'Language', 'Programming']