def _read_until(term, pattern, timeout):
"""
Convenience read-until-pattern function, supporting :meth:`~.get_location`.
:arg blessed.Terminal term: :class:`~.Terminal` instance.
:arg float timeout: timeout period, may be set to None to indicate no
timeout (where 0 is always returned).
:arg str pattern: target regular expression pattern to seek.
:rtype: tuple
:returns: tuple in form of ``(match, str)``, *match*
may be :class:`re.MatchObject` if pattern is discovered
in input stream before timeout has elapsed, otherwise
None. ``str`` is any remaining text received exclusive
of the matching pattern).
The reason a tuple containing non-matching data is returned, is that the
consumer should push such data back into the input buffer by
:meth:`~.Terminal.ungetch` if any was received.
For example, when a user is performing rapid input keystrokes while its
terminal emulator surreptitiously responds to this in-band sequence, we
must ensure any such keyboard data is well-received by the next call to
term.inkey() without delay.
"""
stime = time.time()
match, buf = None, u''
# first, buffer all pending data. pexpect library provides a
# 'searchwindowsize' attribute that limits this memory region. We're not
# concerned about OOM conditions: only (human) keyboard input and terminal
# response sequences are expected.
while True:
# block as long as necessary to ensure at least one character is
# received on input or remaining timeout has elapsed.
ucs = term.inkey(timeout=_time_left(stime, timeout))
if ucs:
buf += ucs
# while the keyboard buffer is "hot" (has input), we continue to
# aggregate all awaiting data. We do this to ensure slow I/O
# calls do not unnecessarily give up within the first 'while' loop
# for short timeout periods.
while True:
ucs = term.inkey(timeout=0)
if not ucs:
break
buf += ucs
match = re.search(pattern=pattern, string=buf)
if match is not None:
# match
break
if timeout is not None:
if not _time_left(stime, timeout):
# timeout
break
return match, buf
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