a

#!/bin/bash
# http://nedbatchelder.com/blog/201107/caged_python.html
short_banner=true

coproc PYTHONSTARTUP= python -i 2>&1
pid=$! read="${COPROC[0]}" write="${COPROC[1]}"

if $short_banner; then
  IFS= read -u$read line || exit
  printf %s\\n "$line"
  while IFS= read -u$read line; do
    [[ _"$line" == _'Type '* ]] && break
  done
  line=
fi

while IFS= read -N1 -u$read c; do
  if [ _"$c" = _$'\n' ]; then
    printf %s\\n "$line"
    line=
    continue
  fi
  line="$line$c"
  case "$line" in
  '>>> '|'... ')
    IFS= read input || break
    [ -z "$input" -a "$line" = '>>> ' ] && line=
    printf %s%s\\n "$line" "$input"
    printf %s\\n "$input" >&$write
    line=
    ;;
  esac
done
exec {write}>&-
wait $pid

b

#!/bin/bash
# http://nedbatchelder.com/blog/201107/caged_python.html
short_banner=true

# both avoid user's PYTHONSTARTUP (if any) and set up our own prompts
coproc PYTHONSTARTUP=<(echo 'import sys; sys.ps1, sys.ps2 = ">>> \n", "... \n"; del sys') python -iu 2>&1
pid=$! read="${COPROC[0]}" write="${COPROC[1]}"

if $short_banner; then
  IFS= read -u$read line || exit
  printf %s\\n "$line"
  while IFS= read -u$read line; do
    [[ _"$line" == _'Type '* ]] && break
  done
  line=
fi

while IFS= read -u$read line; do
  case "$line" in
  '>>> '|'... ')
    IFS= read input || break
    [ -z "$input" -a "$line" = '>>> ' ] && line=
    printf %s%s\\n "$line" "$input"
    printf %s\\n "$input" >&$write
    ;;
  *)
    printf %s\\n "$line"
  esac
done
exec {write}>&-
wait $pid