Configuration utility, to run in a different process.

conf.py

#!/bin/python

# Copyright (c) 2017 Martin McDonough

# Permission to use, copy, modify, and distribute this software for any
# purpose with or without fee is hereby granted, provided that the above
# copyright notice and this permission notice appear in all copies.

# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

import json
import os
from sys import stdin
from tempfile import NamedTemporaryFile

conf_filename = "conf.json"

# If the file doesn't already exist, create it with an empty object insie it.
if not os.path.isfile(conf_filename):
    conf_file = open(conf_filename, "wb")
    conf_file.write("{}\n")
    conf_file.close()
    conf = {}
else:
    conf_file = open(conf_filename, "rb")
    conf = json.load(conf_file)
    conf_file.close()

buffer = ""

while 1:
    c = stdin.read(1)
    if c == '\n':
        
        line = buffer
        
        # Trim away any newline
        if line[-1] == '\n':
            line = line[:-1]
        
        at = line.find('=')
        
        # if an equals was found, then this is an assignment
        if at != -1:
            # Split the input at the equals. Everything before it is the key,
            # everything after is the value.
            key = line[:at]
            value = line[at+1:]
            
            is_number = True
            is_float = False
            for c in value:
                if c == '.':
                    is_float = True
                elif not c.isdigit():
                    is_number = False
                    break
            
            if is_number:
                if is_float:
                    value = float(value)
                else:
                    value = int(value)
            elif value == "true":
                value = True
            elif value == "false":
                value = False
            
            conf[key] = value
            # Write the results to a temporary file. This way if we crash or
            # something, we don't clobber the existing conf.
            temp_conf_file = NamedTemporaryFile(delete = False)
            json.dump(conf, temp_conf_file, indent=4)
            temp_conf_file.close()
            
            # Writing successful, now overwrite the conf file with the temp file.
            os.rename(temp_conf_file.name, conf_filename)
            
        else:
            # This was not an assignment, return the value
            value = conf[line]
            if type(value) == type(True):
                if value:
                    value = "true"
                else:
                    value = "false"
            else:
                value = str(value)
            print (line + "=" + value)
        
        buffer = ""
    else:
        buffer += c.lower()