[docs] [issue15068] fileinput requires two EOF when reading stdin

[Antoine Pitrou]

Antoine Pitrou <pitrou at free.fr> added the comment:

It is unlikely to be solvable at the Python level. Witness the raw stream's behaviour (in Python 3):

>>> sys.stdin.buffer.raw.read(1000)

If you type a letter followed by ^D (Linux) or ^Z (Windows), this returns immediately:

>>> sys.stdin.buffer.raw.read(1000)
x^Db'x'

But since the result is non-empty, the buffering layer will not detect the EOF and will call read() on the raw stream again (as the 1000 bytes are not satisfied). To signal EOF to the buffered stream, you have to type ^D or ^Z *without preceding it with another character*. Try the following:

>>> sys.stdin.buffer.read(1000)

You'll see that as long as you type a letter before ^D or ^Z, the read() will not return (until you type more than 1000 characters, that is):
- ^D alone: returns!
- a letter followed by ^D: doesn't return
- a letter followed by ^D followed by ^D: returns!
- a letter followed by ^D followed by a letter followed by ^D: doesn't return

This is all caused by the fact that a C read() on stdin doesn't return until either the end of line or EOF (or the requested bytes number is satisfied). Just experiment with:

>>> os.read(0, 1000)

That's why I say this is not solvable at the Python level (except perhaps with bizarre ioctl hackery).

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nosy: +pitrou

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<http://bugs.python.org/issue15068>
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