A simple example of a key-value (kv) storage and lookup service, accessible over http/rest

simple_kv_service.py

#!/usr/bin/env python3

"""
simple_kv_service.py

A simple example of a key-value (kv) storage and lookup service,
accessible over http/rest:

http://[host]:[port]/set?somekey=somevalue  => assigns "somevalue" to "somekey"
http://[host]:[port]/get?key=somekey        => looks up "somekey" and returns its value, if it exists

"""

from http.server import BaseHTTPRequestHandler, HTTPServer
from urllib.parse import urlsplit, parse_qsl
from itertools import starmap


class Database:
    def __init__(self):
        self.db = {}

    def get_value(self, key):
        print('looking for %s => %s' % (key, self.db.get(key)))
        return self.db.get(key)

    def set_value(self, key, value):
        print('adding: %s => %s' % (key, value))
        self.db[key] = value


class Handler(BaseHTTPRequestHandler):
    def _get_values(self, keys):
        if len(keys) == 0:
            return self.send_error(404)

        self.send_response(200)
        self.send_header('Content-type', 'text/html')
        self.end_headers()
        for match in map(self.server.db.get_value, keys):
            if match:
                self.wfile.write(match.encode())
            else:
                self.wfile.write(b'[no match found!]')
            self.wfile.write(b'\r\n')
        return

    def _set_values(self, tuples):
        """
        Since set_value() takes two inputs, itertools.starmap
        is simpler than using plain map here.
        """

        list(starmap(self.server.db.set_value, tuples))
        return

    def do_GET(self):
        if self.path.startswith("/set"):
            # parse_qsl() produces a list of (k,v) tuples from the query string
            self._set_values(parse_qsl(urlsplit(self.path).query))
        elif self.path.startswith("/get"):
            # we only want the values whose key was literally "key"
            self._get_values([x[1] for x in parse_qsl(urlsplit(self.path).query) if x[0] == 'key'])
        else:
            # bad request
            self.send_error(400)


class Server:
    def __init__(self, host, port, db):
        server = HTTPServer((host, port), Handler)
        server.db = db
        server.serve_forever()


if __name__ == '__main__':
    database = Database()
    main = Server('', 4000, database)