Python, typeerror about string and bytes

Question

I used Youtube API and got list of comments. And trying to change it into single string so I can use konlpy.

    a = str(' '.join(c)).encode("UTF-8")

But I got

"TypeError: sequence item 0: expected str instance, bytes found"

So I tried

    a = str(b' '.join(c)).encode("UTF-8")

It pops

"TypeError: sequence item 0: expected a bytes-like object, str found"

What is the problem?

+) Input c is...

 response = api_obj.commentThreads().list(part='snippet,replies', videoId=viedoIdd, maxResults=100).execute()

while response:
    for item in response['items']:
        comment = item['snippet']['topLevelComment']['snippet']
        comments.append([comment['textDisplay']])

for c in comments:
    a = str(' '.join(c)).encode("UTF-8")
    words.append(a)