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Assume this simple script for reading from stdin:
```python
#! /usr/bin/env python3
import sys
import os
import asyncio
async def main(loop):
 done = False
 fileno = sys.stdin.fileno()
 def _reader():
 nonlocal done
 chunk = os.read(fileno, 1024)
 if not chunk:
 loop.remove_reader(fileno)
 done = True
 return
 print(chunk.decode(), end='')
 loop.add_reader(fileno, _reader)
 while not done:
 await asyncio.sleep(1)
if __name__ == '__main__':
 main_loop = asyncio.get_event_loop()
 main_loop.run_until_complete(main(main_loop))
```
When I run it by:
```bash
$ ./stdin_issue.py <<EOF
> hello
> EOF
```
I get:
```
Traceback (most recent call last):
 File "/usr/lib/python3.5/asyncio/selector_events.py", line 234, in add_reader
 key = self._selector.get_key(fd)
 File "/usr/lib/python3.5/selectors.py", line 191, in get_key
 raise KeyError("{!r} is not registered".format(fileobj)) from None
KeyError: '0 is not registered'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
 File "./stdin_issue.py", line 41, in <module>
 main_loop.run_until_complete(main(main_loop))
 File "/usr/lib/python3.5/asyncio/base_events.py", line 387, in run_until_complete
 return future.result()
 File "/usr/lib/python3.5/asyncio/futures.py", line 274, in result
 raise self._exception
 File "/usr/lib/python3.5/asyncio/tasks.py", line 239, in _step
 result = coro.send(None)
 File "./stdin_issue.py", line 34, in main
 loop.add_reader(fileno, _reader)
 File "/usr/lib/python3.5/asyncio/selector_events.py", line 237, in add_reader
 (handle, None))
 File "/usr/lib/python3.5/selectors.py", line 411, in register
 self._epoll.register(key.fd, epoll_events)
PermissionError: [Errno 1] Operation not permitted
```
But the:
```bash
echo "Hello" | ./stdin_issue.py 
```
 Is working well.
I was already tried this with the `select.select` directly, and it working:
```
def using_select():
 files = [sys.stdin.fileno()]
 while True:
 readables, _, errors = select(files, [], files)
 if errors:
 print('ERROR:', errors)
 return
 if readables:
 for f in readables:
 chunk = os.read(f, 1024)
 if not chunk:
 return
 print(chunk.decode(), end='')
```

Checked latest master (c879ff247ae1b67a790ff98d2d59145302cd4e4e), 3.8 - 3.5 branches - can not reproduce.
OS - macOS

If fd is a regular file it is not supported well by all select/poll/epoll.
Registration may succeed but the data is marked as "already ready for reading".
Not sure if we should do anything.
The situation may be changed after eventual providing asyncio API for files (there is no actual work for it yet).