如何仅使用readline（）从文件读取

Question

The code i have right now is this

f = open(SINGLE_FILENAME)
lines = [i for i in f.readlines()]

but my proffessor demands that

You may use readline(). You may not use read(), readlines() or iterate over the open file using for.

any suggestions? thanks

Answer 1

You could use a two-argument iter() version :

lines = iter(f.readline, "")

If you need a list of lines:

lines = list(lines)

Answer 2

First draft:

lines = []
with open(SINGLE_FILENAME) as f:
    while True:
        line = f.readline()
        if line:
            lines.append(line)
        else:
            break

I feel fairly certain there is a better way to do it, but that does avoid iterating with for, using read, or using readlines.

You could write a generator function to keep calling readline() until the file was empty, but that doesn't really seem like a large improvement here.