Sample use cases

Let's summarize our learning in the chapter using a couple of sample use cases.

First use case

Consider the first scenario as follows:

A travel agency has three customers. For our use case, the requirement is to suggest a package for a specific city using the predefined preferences for any two customers. As an additional output or suggestion, there needs to be a suggestion on weather status for the next five days. Also, to provide an enhanced end user experience, ask a single question to determine check-in time and type of transport for the journey.

The code is as follows:

...
import getpass 
import base64
import requests
from collections import Counter
import re

#ask for username .. will be displayed when typed
uname=input("Enter your username :")

#ask for password ... will not be displayed when typed
#(try in cmd or invoke using python command)
p = getpass.getpass(prompt="Enter your password: ")

#construct credential with *.* as separator between username and password
creds=uname+"*.*"+p

#encrypted creds of the registered customers
#for testing username:password is customer1:password1 , customer2:password2, and so on

#create a dictionary:
customers={
    "customer1":b'Y3VzdG9tZXIxKi4qcGFzc3dvcmQx',
    "customer2":b'Y3VzdG9tZXIyKi4qcGFzc3dvcmQy',
    "customer3":b'Y3VzdG9tZXIzKi4qcGFzc3dvcmQz'
    }

###Decrypt a given set of credentials 
def decryptcredential(pwd):
    rvalue=base64.b64decode(pwd)
    rvalue=rvalue.decode()
    return rvalue
###Encrypt a given set of credentials
def encryptcredential(pwd):
  rvalue=base64.b64encode(pwd.encode())
  return rvalue

#to validate if a customer is legitimate
flag=True

### procedure for validated customer
def validatedcustomer(customer):
    print ("Hello "+customer)
    inputcity=input("Which city do you want to travel (ex London/Paris/Chicago): ")
    inputaddinfo=input("Any specific checkin time [AM/PM] and preferred mode of travel [car/bus]: ")

    #### extract the regex values from additional info
    regex=re.compile('\d+:\d+\s[AP]M')
    time=re.findall(regex,inputaddinfo)
    if "car" in inputaddinfo:
        transport="car"
    else:
        if "bus" in inputaddinfo:
            transport="bus"

    ### create sentence based upon the additional info provided
    print ("\n\nYou have selected to checkin at "+time[0]+", and your preferred transport will be "+transport+" .")
    
    getcityinfo=validatecity(inputcity)

    ### this is to sort the dictionary from highest to lowest based upon weather types
    sorted_d = [(k, getcityinfo[k]) for k in sorted(getcityinfo, key=getcityinfo.get, reverse=True)]
    
    ###iterate through the weathers to construct a sentence
    sentence="Weather prediction for next 5 days is (chance of) "
    for item in sorted_d:
        sentence=sentence+" "+item[0]+": "+str(item[1])+"%,"
    print (sentence)
        
### to validate the average weather for that city for next 5 days
def validatecity(inputcity):
    #create empty list
    weathers=[]
    weatherpercentage={}
    #remove any additional spaces accidentally entered
    inputcity=inputcity.strip()
    urlx="https://samples.openweathermap.org/data/2.5/forecast?q="+inputcity+"&appid=b6907d289e10d714a6e88b30761fae22"
    #send the request to URL using GET Method
    r = requests.get(url = urlx)
    output=r.json()
    ### this is to parse the type of weather and count them in a list
    for item in output['list']:
        weathers.append(item['weather'][0]['description'])
    countweather=Counter(weathers)
    #### this is to find the percentage of each weather type from the given output (36 variations are returned from API)
    for item in countweather:
        weatherpercentage[item]=int((countweather[item]/36) * 100)
    return weatherpercentage 
    
### validate if the username is part of any customers
if (uname in customers):
    encryptedcreds=encryptcredential(creds)
    getcustomercreds=customers[uname]
    ### validate if the credentials provided is the same as stored credentials for that customer
    if not(str(encryptedcreds.decode()) == str(getcustomercreds.decode())):
        flag=False
else:
    flag=False    

if not(flag):
    print ("Unauthorized customer.")
else:
    validatedcustomer(uname)

Scenario 1: Incorrect username and password:

C:\gdrive\book2\github\edition2\chapter1>python use_case1.py
Enter your username :abhishek
Enter your password:
Unauthorized customer.

Scenario 2: Correct username but incorrect password:

C:\gdrive\book2\github\edition2\chapter1>python use_case1.py
Enter your username :customer1
Enter your password:
Unauthorized customer.

C:\gdrive\book2\github\edition2\chapter1>

Scenario 3: Correct username and password:

C:\gdrive\book2\github\edition2\chapter1>python use_case1.py
Enter your username :customer1
Enter your password:

Hello customer1
Which city do you want to travel (ex London/Paris/Chicago): paris
Any specific checkin time [AM/PM] and preferred mode of travel [car/bus]: travel checkin at 12:30 PM by bus

You have selected to checkin at 12:30 PM, and your preferred transport will be bus .
Weather prediction for next 5 days is (chance of) clear sky: 61%, light rain: 27%, few clouds: 5%, broken clouds: 2%, moderate rain: 2%,

C:\gdrive\book2\github\edition2\chapter1>

As we can see in the preceding output, the customer selected paris, with a check in time of 12:30 PM and bus as their mode of transport.

Based upon the location selected, the API call was made to the weather site, and a prediction of the weather for the next 5 days was returned in JSON. This has been evaluated in terms of a percentage, and a result value was given, which predicts a 61% chance of clear sky, followed by a 27% chance of light rain.

Let's run this output for another customer:

C:\gdrive\book2\github\edition2\chapter1>python use_case1.py
Enter your username :customer2
Enter your password:
Hello customer2
Which city do you want to travel (ex London/Paris/Chicago): Chicago
Any specific checkin time [AM/PM] and preferred mode of travel [car/bus]: checkin preferred at 10:00 AM and travel by car


You have selected to checkin at 10:00 AM, and your preferred transport will be car .
Weather prediction for next 5 days is (chance of) clear sky: 51%, light rain: 37%, few clouds: 5%, broken clouds: 2%, moderate rain: 2%,

C:\gdrive\book2\github\edition2\chapter1>

In this particular situation, we see that customer2 has a check-in preference of 10:00 AM and prefers to travel by car.

Also, as per their selection of Chicago, the prediction of the weather is clear sky: 51%, light rain: 37%, few clouds: 5%, broken clouds: 2%, moderate rain: 2%.

In a similar way, we can call additional APIs to find out the traffic/weather, and even currency values for a particular city for any given dates. This can be made an extensive application that can predict the user's journey based upon their destination and date selections.

Second use case

Consider the second scenario as follows:

As an admin, you need to provide a script to users to add/delete themselves based upon authentication status and if authenticated successfully, provide an option to change their passwords:

...
import getpass 
import base64
import os.path

###Check with credential storage file exists. If not, then create one, otherwise read data from the current file
storedcreds=[]
if (os.path.isfile("usecase_creds.txt")):
    fopen=open("usecase_creds.txt")
    storedcreds=fopen.readlines()
else:
    fopen=open("usecase_creds.txt","w")

###Decrypt a given set of credentials 
def decryptcredential(pwd):
    rvalue=base64.b64decode(pwd)
    rvalue=rvalue.decode()
    return rvalue

###Encrypt a given set of credentials
def encryptcredential(pwd):
  rvalue=base64.b64encode(pwd.encode())
  return rvalue

#### this is used to deregister a authenticated user
def deregister(getencryptedcreds):
    with open("usecase_creds.txt") as f:
        newText=f.read().replace(getencryptedcreds+"\n","")

    with open("usecase_creds.txt", "w") as f:
        f.write(newText)
    print ("you are deregistered")
    
#this is to store the read encrypted creds from file into expanded username and password combo
storedcredsexpanded=[]
for item in storedcreds:
    item=item.strip()
    #to ensure we do not parse the blank values or blank lines
    if (len(item) > 2):
        tmpval=decryptcredential(item)
        storedcredsexpanded.append(tmpval)

#ask for username .. will be displayed when typed
uname=input("Enter your username :")

#ask for password ... will not be displayed when typed
#(try in cmd or invoke using python command)
p = getpass.getpass(prompt="Enter your password: ")

#construct credential with *.* as separator between username and password
creds=uname+"*.*"+p

#encrypted creds of the registered customers
#for testing username:password is customer1:password1 , customer2:password2, and so on...
getencryptedcreds=encryptcredential(creds)

#validate authentication of user
flag=False
usrauthenticated=False
for item in storedcreds:
    if (getencryptedcreds.decode() in item):
        flag=True

if (flag):
    print ("Authenticated successfully")
    usrauthenticated=True
else:
    print ("Authentication failed")
    #validate if user exists
    tmpvalue=decryptcredential(getencryptedcreds)
    #split username and password
    tmpvalue=tmpvalue.split("*.*")
    usrflag=False
    ###validate if this username exists otherwise give an option for new registration
    for item in storedcredsexpanded:
        item=item.split("*.*")
        if (tmpvalue[0] == item[0]):
            print ("User already exists but password incorrect. Please contact Admin for password reset")
            usrflag=True
            break
    #if user does not exist
    if (usrflag==False):
            readinput=input("User does not exist, Do you want to register yourself (Y/N) ")
            readinput=readinput.strip()
            readinput=readinput.lower()
            if (readinput == "y"):
                uname=input("Enter your username :")
                p = getpass.getpass(prompt="Enter your password: ")
                creds=uname+"*.*"+p
                getencryptedcreds=encryptcredential(creds)
                ## to convert bytes to string
                getencryptedcreds=getencryptedcreds.decode()

                ##open file in append mode
                fopen=open("usecase_creds.txt","a")
                fopen.write(getencryptedcreds+"\n")
                fopen.close()
                print ("User added successfully")

if (usrauthenticated):
    readinput=input("Do you want to deregister yourself (Y/N) ")
    readinput=readinput.strip()
    readinput=readinput.lower()
    if (readinput == "y"):
        deregister(getencryptedcreds.decode())
    else:
        readinput=input("Do you want to change your password (Y/N) ")
        readinput=readinput.strip()
        readinput=readinput.lower()
        if (readinput == "y"):
            p = getpass.getpass(prompt="Enter your password: ")
            creds=uname+"*.*"+p
            newencryptedcreds=encryptcredential(creds)
            newencryptedcreds=newencryptedcreds.decode()
            getencryptedcreds=getencryptedcreds.decode()

            ###updated the credential of the user
            with open("usecase_creds.txt") as f:
                newText=f.read().replace(getencryptedcreds, newencryptedcreds)

            with open("usecase_creds.txt", "w") as f:
                f.write(newText)
            print ("Your password is updated successfully")

The outputs based upon different scenario are as follows:

Scenario 1: A user who is not registered receives the following output:

C:\gdrive\book2\github\edition2\chapter1>python use_case2.py
Enter your username :newcustomer
Enter your password:
Authentication failed
User does not exist, Do you want to register yourself (Y/N) y
Enter your username :newcustomer
Enter your password:
User added successfully

C:\gdrive\book2\github\edition2\chapter1>

Scenario 2: A user who is registered but forgot their password receives this output:

C:\gdrive\book2\github\edition2\chapter1>python use_case2.py
Enter your username :newcustomer
Enter your password:
Authentication failed
User already exists but password incorrect. Please contact Admin for password reset

C:\gdrive\book2\github\edition2\chapter1>

Scenario 3: A user who is a registered customer, and wants to change their password if authenticated successfully, receives the following output:

C:\gdrive\book2\github\edition2\chapter1>python use_case2.py
Enter your username :customer2
Enter your password:
Authenticated successfully
Do you want to deregister yourself (Y/N) n
Do you want to change your password (Y/N) y
Enter your password:
Your password is updated successfully

Scenario 4: A user who is a registered customer, and want to deregister themselves if authenticated successfully, receives the following output:

C:\gdrive\book2\github\edition2\chapter1>python use_case2.py
Enter your username :newcustomer
Enter your password:
Authenticated successfully
Do you want to deregister yourself (Y/N) y
you are deregistered

C:\gdrive\book2\github\edition2\chapter1>

All of these preceding operations are saved in the background, using the file operations, under the file named usecase_creds.txt:

Additionally, as an example, here is the current output of usecase_creds.txt, which shows that none of the credentials storage in the file occurs in clear-text (or human-readable format):

C:\gdrive\book2\github\edition2\chapter1>more usecase_creds.txt
Y3VzdG9tZXIxKi4qcGFzc3dvcmQx
Y3VzdG9tZXIyKi4qbmV3cGFzc3dvcmQ=
YWJoaXNoZWsqLipoZWxsb3dvcmxk

C:\gdrive\book2\github\edition2\chapter1>

This sample use case is very useful when we have multiple people using scripts, as well as places where authentications are involved. A key focus here is that all the transactions (including data storage) are encrypted and no clear, unencrypted storage of any information is used.