f = open("io/data/file1")
print(f.readline())
print(f.readline(3))
print(f.readline(4))
print(f.readline(5))
print(f.readline())

# readline() on writable file
f = open('io/data/file1', 'ab')
try:
    f.readline()
except OSError:
    print('OSError')
f.close()
