For one-off simple calculations I just use awk, with this handy function in my .bashrc:

  function calc() { awk "BEGIN{print $*}"; }
  
  # usage in bash
  $ calc 'sqrt(25) + 2**3 - 17.17'
  -4.17

Yes! (although ruby (irb) instead of python). It's amazingly useful to be able plug in expressions in a single line of text format. Though for more complex expressions, something like qalculate looks nice to me.

yes, with modifications - https://github.com/idanpa/calcpy

bc -l