Two examples of running python inside a bash script. The first is a simple one that just returns a result while the second gives bash a series of commands to run or a result to print (such as from parsing command line arguments).

run_python_in_bash.sh

#!/usr/bin/env bash

############################################################################
################################## Intro ###################################
############################################################################

# Example on how to run python inside of bash. Anything that is printed
# in the python part is "returned" to bash
#
# Examples:
#     Simple: Just return the output
#     Complex: Tell bash which commands to run and/or print results from
#              parsing the command-line arguments
#
# Why:
#     This is useful when you want to be able to 'source script.sh' and/or
#     when you need to be able to use certain environment variables and paths
#     such as bash environment modules.
#     
#     For many uses, python subprocess is a *MUCH* better solution
# 
# Gotchas:
#     There are a few things to know about writing these combined scripts:
#         * Bash variables will be expanded! This can be useful, but may
#           also cause problems
#         * Certain characters, even when in python string, must be escped or 
#           avoided. The most notable example is the backtick "`"
#         * sys.argv in python is what is passed! Not the one for the script.
#           See the second invocation for "Simple Example"

############################################################################
############################## Simple Example ##############################
############################################################################

# This example is just to do some minor processing.

adder(){
python - "$@" <<ENDPY
import sys

tot = 0.0
for arg in sys.argv[1:]:
    tot = tot + float(arg)

# return
print(tot)

ENDPY
}

# These are commented out for the complex example below.
#echo $(adder 1 2 3.4) # Add specific arguments
#echo $(adder "$@")    # Add the arguments from the command line 

############################################################################
############################# Complex Example ##############################
############################################################################

# This example demonstrates some more advanced usage. This is, of course, a
# toy problem but it demonstrates how to use python do build a complex
# command. As noted in the Intro, this is useful when you want to execute
# a series of bash commands in the primary bash environment (and potentially
# with a "source myscript.sh" invocation)

# Remember that variables are filled in
VERSION='20180427'
PROG='adder-example'

# This is used as a sentinel to later execute vs just echo. This is NOT the 
# main example
execflag=$(python -c "import random;print(''.join(random.choice('abcdefghijklmnopqrstuvwxyz') for _ in range(50)))")


adder_cli() {
python - "$@" <<ENDPY
from __future__ import division, print_function, unicode_literals

__version__ = $VERSION

import sys
import argparse

sys.argv[0] = "$PROG" # Force the name

description="""
Add (or subtract if set) command line arguments. Print them to the screen
and then *also* write to a file. (recall this is a toy example)
"""

parser = argparse.ArgumentParser(description=description,epilog='version: $VERSION')

parser.add_argument('--neg',action='store_true',help='Negate the sum')
parser.add_argument('num',nargs='+',help='number to add')

args = parser.parse_args(sys.argv[1:])

# Send in the execflag so everything else gets evaluated by bash
print('${execflag}')

tot = sum(float(a) for a in args.num)
if args.neg: tot = -1.0*tot

bashcmd = []
bashcmd.append('echo "The sum in: {}"'.format(tot))
bashcmd.append('echo "The sum in: {}" >> exampleout'.format(tot))

for cmd in bashcmd:
    print(cmd)

ENDPY
}


# This part calls the python code and then either executes it or
# just prints the result

cmd=$(adder_cli "$@")
if [[ "$cmd" == ${execflag}* ]]; then
    # Means we run it
    IFS= # Makes it not break at new lines
    cmd="$(echo $cmd | sed "s/${execflag}//g")"
    
    IFS=$'\n'
    for line in $cmd; do
        echo "[$PROG] executing: \$ ${line}"
        eval "$line"
    done    
else
    echo "$cmd"
fi