The current implementation tries to (1) patch the existing readline
module definition if it's already present in the inittab and (2) append
our patched readline module to the inittab. The former (1) uses the
non-stable Python API and I can't find a situation where this is
necessary.
We do this work before initialization, so for the readline
module to exist, it either needs to be added by Python itself (which
doesn't seem to be the case), or someone would have had to have added it
without initializing.
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