Call Python script on request - Python server

First of all, the python code you've posted is broken, if you did copy&paste from your own script, then your code is invalid python because the indentation is wrong.

Secondly, it's a bad idea to just execute a script with exec, this can be dangerous, specially if you are not the owner of the script and how knows what the script does.

So let's modify your root/externalFunc.py first: let's add a run method that does the work of the script. Instead of just printing to the standard output, the run function should return something, for example the a string or a dictionary containing the results.

Because you haven't shown us the code of root/externalFunc.py, I assume that the script may look like this:

#!/usr/bin/env python
# root/externalFunc.py
# old version

def run():
    # ... doing some work,
    # result is a variable with the result
    print "Result: %d" % result

if __name__ == '__main__':
    main()

Now let's modify it.

1. create an empty file __init__.py in the root/ directory:

   // on linux/mac/bsd
   $ touch root/__init__.py
   
   // on windows
   cmd> type NUL > root/__init__.py
   

This allows to use from root.whatever export something in another module.

2. Let's add a run method that actually does the work:

The new version:

#!/usr/bin/env python
# root/externalFunc.py
# new version

import sys

def run(parm1, param2, param3):
    # ... doing some work,
    # result is a variable with the result

    return = {
        "success": True,
        "value": result
    }

def main():
    if len(sys.argv) != 4:
        print >> sys.stderr, "usage: %s param1 param2 param3" % sys.argv
        return 1
    param1 = int(sys.argv[1])
    param2 = sys.argv[2]
    param3 = int(sys.argv[3])

    res = run(param1, param2, param3)
    if res["success"]:
        print "Result: %d" % res["value"]
        return 0
    else:
        print "Error, ..."
        return 1

if __name__ == '__main__':
    return main()

Now we have to change your server code to import the run method and use that method instead of using exec or execfile

from BaseHTTPServer import BaseHTTPRequestHandler, HTTPServer
from root.externalFunc import run as externalFunc_run

class KodeFunHTTPRequestHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        param1 = 3
        param2 = "max"
        param3 = -12

        res = externalFunc_run(param1, param2, param3)

        if res["success"]:
            answer = "The result is: %d" % res["value"]
        else:
            answer = "Error while computing externalFunc"

        #send code 200 response
        self.send_response(200)

        #send header first
        self.send_header('Content-type','text/plain')
        self.end_headers()

        # send answer
        self.wfile.write(answer)

Now if you don't want (or cannot) change the code of root/externalFunc.py, or the script is not a python script, then you could use subprocess.check_output.

import subprocess
import shlex

# bad, don't do that
# exec("root/externalFunc.py")

# do this instead
answer = subprocess.check_output(shlex.split("root/externalFunc.py params..."))
print "Answer: %s" % answer

Using subprocess.check_output is much more safe, behind the scenes it calls subprocess.Popen, which executes a child program in a new process, thus the child program won't cause damage if it goes bersek.

Now you can replace this line res = externalFunc_run(param1, param2, param3) with the subprocess.check_output line.