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Fix slow multiline evaluation due to pexpect sleeps #160

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Fix slow multiline evaluation due to pexpect sleeps #160

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8 changes: 8 additions & 0 deletions bash_kernel/kernel.py
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Original file line number Diff line number Diff line change
Expand Up @@ -122,6 +122,14 @@ def _start_bash(self):
bashrc = os.path.join(os.path.dirname(pexpect.__file__), 'bashrc.sh')
child = pexpect.spawn("bash", ['--rcfile', bashrc], echo=False,
encoding='utf-8', codec_errors='replace')
# pexpect sleeps for delaybeforesend milliseconds (default 50)
# before every send, and run_command submits a cell one line at a
# time, so this adds ~50ms per line -- multiple seconds for a large
# cell. We only ever send just after seeing a prompt, so the delay
# (which guards against a TTY echo race -- see pexpect's rationale)
# is redundant here.
# https://github.com/pexpect/pexpect/blob/aa989594e1e413f45c18b26ded1783f7d5990fe5/pexpect/pty_spawn.py#L136-L150
child.delaybeforesend = 0
# Following comment stolen from upstream's REPLWrap:
# If the user runs 'env', the value of PS1 will be in the output. To avoid
# replwrap seeing that as the next prompt, we'll embed the marker characters
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