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Description
Bug report
When running the interpreter (python -i) the REPL appears to implement its own buffering, independent ofsys.stdin and its internal buffer.
Consider the following (working) example, manually entered into the REPL via the keyboard:
$ python3 -iPython 3.11.0 (main, Oct 24 2022, 00:00:00) [GCC 12.2.1 20220819 (Red Hat 12.2.1-2)] on linuxType "help", "copyright", "credits" or "license" for more information.>>> import sys>>> print('hello', sys.stdin.readline())worldhello world>>>This appears to work only because at the time I hit<enter> after theprint() line, theworld isn't available to read yet, and therefore the repl can't possibly consume it. If I put the whole thing into a file, andcat it in one go, however:
$ cat example.py import sysprint('hello', sys.stdin.readline())world$ cat example.py | python3 -i ST 12 peer Python 3.11.0 (main, Oct 24 2022, 00:00:00) [GCC 12.2.1 20220819 (Red Hat 12.2.1-2)] on linuxType "help", "copyright", "credits" or "license" for more information.>>> >>> hello >>> Traceback (most recent call last): File "<stdin>", line 1, in <module>NameError: name 'world' is not defined>>> >>>We can see thatreadline() returns nothing at all, becauseworld has already been consumed by the repl, which attempts (and fails) to interpret it as the next command to be executed.
You can work around this issue by inserting even the tiniest of pauses. Consider:
$ cat example.pyimport sysprint('hello', sys.stdin.readline())$ (cat example.py; echo world) | python3 -iPython 3.11.0 (main, Oct 24 2022, 00:00:00) [GCC 12.2.1 20220819 (Red Hat 12.2.1-2)] on linuxType "help", "copyright", "credits" or "license" for more information.>>> >>> hello >>> Traceback (most recent call last): File "<stdin>", line 1, in <module>NameError: name 'world' is not defined>>>(ie: broken)
but:
$ (cat example.py; sleep 0.1; echo world) | python3 -iPython 3.11.0 (main, Oct 24 2022, 00:00:00) [GCC 12.2.1 20220819 (Red Hat 12.2.1-2)] on linuxType "help", "copyright", "credits" or "license" for more information.>>> >>> hello world(ie: working).
Your environment
Stockpython3-3.11.0-1.fc37.x86_64 package installed on Fedora 37.