Python 3 web calculator with POST

python3webcalculator.py

#!/usr/bin/python3
# This is a script written as homework for computer science
# (c) 2018 Marco Marinello <[email protected]>

# Import modules
from http.server import BaseHTTPRequestHandler,HTTPServer
import views

# Import settings
try:
    from settings import *
except Exception as e:
    print("Unable to load settings, %s occurred" % e)


URLS = {
    "": views.index,
    "/": views.index,
    "/index.html": views.index,
    "/compute": views.compute,
    "#404": views.e404
}


class WebCalculatorHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path in URLS:
            URLS[self.path](self, posting=False)
            return
        # Custom 404 error page
        URLS["#404"](self, posting=False)
        return

    def do_POST(self):
        if self.path in URLS:
            URLS[self.path](self, posting=True)
            return
        # Custom 404 error page
        URLS["#404"](self, posting=True)
        return


try:
    server = HTTPServer(('0', PORT), WebCalculatorHandler)
    print("Server running on 0:%s" % PORT)
    server.serve_forever()
except KeyboardInterrupt:
    print("CTRL+C pressed, exiting...")
    server.socket.close()

exit()

settings.py

PORT = 8000

utils.py

#!/usr/bin/python3
# This is a script written as homework for computer science
# (c) 2018 Marco Marinello <[email protected]>

import cgi


def render(request, filename, substitutions=None, state=200):
    try:
        h = open("templates/%s" % filename, "r")
    except IOError:
        print("%s cannot be found" % filename)
        request.send_error(500, "Template not found")
        return

    content = h.read()
    h.close()

    if substitutions:
        content = content.format(**substitutions)

    request.send_response(state)

    if ".htm" in filename:
        request.send_header("Content-type", "text/html")

    request.end_headers()

    # bytes are requested to send output, encoding needed
    request.wfile.write(content.encode("utf-8"))

    return


def redirect(request, url):
    request.send_response(301)
    request.send_header("Location", url)
    request.end_headers()
    return


def parse_post(request):
    form = cgi.FieldStorage(
        fp=request.rfile,
        headers=request.headers,
        environ={
            'REQUEST_METHOD':'POST',
            'CONTENT_TYPE':request.headers['Content-Type'],
        }
    )

    return form


def parse_number(x):
    try:
        v = int(x)
    except ValueError:
        try:
            v = float(v)
        except:
            raise Exception("Not a number")
    return v

views.py

#!/usr/bin/python3
# This is a script written as homework for computer science
# (c) 2018 Marco Marinello <[email protected]>

from utils import render, redirect, parse_post, parse_number


def index(request, posting):
    render(request, "index.html")


def e404(request, posting):
    render(request, "404.html", state=404)


def compute(request, posting):
    if not posting:
        redirect(request, "/")
        return

    # Parse form Content
    _POST = parse_post(request)

    # First of all check the two numbers
    try:
        n1 = parse_number(_POST["n1"].value)
        n2 = parse_number(_POST["n2"].value)
    except Exception as e:
        print(e)
        render(request, "result.html", substitutions={"result": "n1 and/or n2 aren't numbers"})
        return

    result = ""
    op = _POST["operation"].value

    if op == "+":
        result = "Result: {} + {} = {}".format(n1, n2, n1+n2)
    elif op == "-":
        result = "Result: {} - {} = {}".format(n1, n2, n1-n2)
    elif op == "x":
        result = "Result: {} x {} = {}".format(n1, n2, n1*n2)
    elif op == ":":
        # convert into float to prevent errors
        n1 = float(n1)
        # n2 will be converted automatically
        result = "Result: {} : {} = {}".format(n1, n2, n1/n2)
    elif op == "^":
        result = "Result: {} ^ {} = {}".format(n1, n2, n1**n2)

    render(request, "result.html", substitutions={"result": result})