python: output in reverse order in one sentence

1. Taking letters as the smallest unit

m = ("i am a man")
def string_reverse(m):
    num=len(m)
    a=[]
    for i in range(num):
        a.append(m[num-1-i])
    return a
b = string_reverse(m)
print(b)

2. Taking words as the smallest unit

m = ("I am a man")
def reverse_sentence(s):

    s = s.split()
    s = " ".join(s[::-1])
    return s


y = reverse_sentence(m)
print(y)

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