How to find out whether a file is at its `eof`?

fp.read() reads up to the end of the file, so after it's successfully finished you know the file is at EOF; there's no need to check. If it cannot reach EOF it will raise an exception.

When reading a file in chunks rather than with read(), you know you've hit EOF when read returns less than the number of bytes you requested. In that case, the following read call will return the empty string (not None). The following loop reads a file in chunks; it will call read at most once too many.

assert n > 0
while True:
    chunk = fp.read(n)
    if chunk == '':
        break
    process(chunk)

Or, shorter:

for chunk in iter(lambda: fp.read(n), ''):
    process(chunk)

The "for-else" design is often overlooked. See: Python Docs "Control Flow in Loop":

Example

with open('foobar.file', 'rb') as f:
    for line in f:
        foo()

    else:
        # No more lines to be read from file
        bar()