Bash to Python Function Mapping

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• Calling Python from bash

Overview

This article describes a method to map bash functions to Python functions. The method is somewhat awkward, and a much better idea would be to write the entire logic in Python, and then call the Python program from a thin bash wrapper, as described here: Running a Python Program with a Bash Wrapper.

Solution

Given an external module my_module.py with the following content:

def my_function(arg1, arg2, arg3):
    print('this is my_function(' + arg1 + ", " + arg2 + ", " + arg3 + ")")

the module can be called generically from a bash script as follows:

#!/usr/bin/env bash

function call-python() {
  local python_interpreter=$1
  local module_path=$2
  local function_name=$3
  [[ -z ${python_interpreter} ]] && fail "'python_interpreter' not provided"
  [[ -z ${module_path} ]] && fail "'module_path' not provided"
  [[ -z ${function_name} ]] && fail "'function_name' not provided"
  shift 3
  local args
  for i in "${@}"; do
    [[ -z ${args} ]] && args="'${i}'" || args="${args}, '${i}'"
  done
  local module_name
  module_name=$(basename "${module_path}" .py)
  # instead of PATH python3 you may want to use the interpreter from a specific virtual environment
  (PYTHONPATH="$(dirname ${module_path})"; export PYTHONPATH; ${python_interpreter} <<EOF
import ${module_name}

${module_name}.${function_name}(${args})
EOF
  )
}

call-python ./my_module.py my_function blue red green

The output will be:

this is my_function(blue, red, green)

⚠️ Numbers will be converted to strings before being passed to the function, the implementation is incomplete.