f = open('ssafy.txt', 'r')
 #all text 전체를 불러온다 (개행문자 포함!)
all_text = f.read()
print(all_text)
f.close

with open('with_ssafy.txt', 'r') as f:
    all_text = f.read()
    print(all_text)

with open('with_ssafy.txt', 'r') as f:
    lines= f.readlines()
    for line in lines:
        print(line.strip()) # 개행 문자 제거! (print 자체에 개행 문자)