[CS50's - Introduction to Python] Libraries

In this post I will show how to solve the problems from topic 4 - Libraries of CS50’s - Introduction to Python course.

Table of Contents

• Emojize
• Frank, Ian and Glen’s Letters
• Adieu, Adieu
• Guessing Game
• Little Professor
• Bitcoin Price Index

Emojize

This problem asks to implement a library that takes user’s input for an emoji code (alias) and print it as an emoji.

First we need to install the emoji library. On the command prompt we do:

pip install emoji

Now we can code:

1. Import the emoji library.
2. Ask for user input.
3. Use the method emojize to convert alias into emoji.
4. Then print it.

import emoji

text = input("Input: ")
text = emoji.emojize(text, language='alias')

print(f"Output: {text}")

GitHub repository

Frank, Ian and Glen’s Letters

This problem asks to use the Frank, Ian, and Glen’s letters format in program that:

• Expects zero or two command-line arguments:
  • Zero if the user would like to output text in a random font.
  • Two if the user would like to output text in a specific font, in which case the first of the two should be -f or --font, and the second of the two should be the name of the font.
• Prompts the user for a str of text.
• Outputs that text in the desired font.
• If the user provides two command-line arguments and the first is not -f or –font or the second is not the name of a font, the program should exit via sys.exit with an error message.

First we need to install the pyfiglet library. On the command prompt we do:

pip install pyfiglet

Now we can code:

1. Import the sys library to take command-line arguments.
2. Import the random library to be abble to use the choice method to choose the font case user do not input the parameter for font.
3. Import the Figlet library.
4. The variable fonts creates a list of fonts from Figlet library.
5. If there is only one argument the font will be set randonly from list fonts.
6. if there is 3 argumnts we verify if the second argument is different of -f or --font or if the font name given by user is not in the list of fonts. If any of these cases are true it will exit the program.
7. If everything is false so we will set the font specified by user.
8. The else means for the case user gives more then three arguments, the program will exit with message Invalid usage
9. After setting the font we ask for user message and print it formated in a Figlet font.

import sys
import random
from pyfiglet import Figlet

figlet = Figlet()
fonts = figlet.getFonts()

if len(sys.argv) == 1:
    figlet.setFont(font=random.choice(fonts))

elif len(sys.argv) == 3:
    if sys.argv[1] != "-f" and sys.argv[1] != "--font" or sys.argv[2] not in fonts:
        sys.exit("Invalid usage")
    figlet.setFont(font=sys.argv[2])
else:
    sys.exit("Invalid usage")

text = input("Input: ")
print(figlet.renderText(text))

GitHub repository

Adieu, Adieu

In this problem we will implement a program that prompts the user for names, one per line, until the user inputs control-d. We will assume that the user will input at least one name. Then bid adieu to those names, separating two names with one and, three names with two commas and one and, and names with commas and one and, as in the below:

Adieu, adieu, to Liesl
Adieu, adieu, to Liesl and Friedrich
Adieu, adieu, to Liesl, Friedrich, and Louisa
Adieu, adieu, to Liesl, Friedrich, Louisa, and Kurt
Adieu, adieu, to Liesl, Friedrich, Louisa, Kurt, and Brigitta
Adieu, adieu, to Liesl, Friedrich, Louisa, Kurt, Brigitta, and Marta
Adieu, adieu, to Liesl, Friedrich, Louisa, Kurt, Brigitta, Marta, and Gretl

First we need to install the inflect library. On the command prompt we do:

pip install inflect

Now we can code:

1. First we import the inflect library. To make it work we also do p = inflect.engine().
2. The array names is set to save the names that user inputs.
3. While the user do not press “control + d” the exception will not be raised and the user will be asked for a name, and it will be included (append method) on the names array.
4. When the user press control-d the exception will be raised and we wil exit the while loop.
5. The names will then be joined to the variable list.
6. And finaly list will be printed to user.

import inflect
p = inflect.engine()
names = []

while True:
    try:
        name = input("Name: ")
        names.append(name)

    except EOFError:
        print()
        break

list = p.join(names)
print(f"Adieu, adieu, to {list}")

GitHub repository

Guessing Game

In this problem we must implement a program that:

• Prompts the user for a level, $n$. If the user does not input a positive integer, the program should prompt again.
• Randomly generates an integer between 1 and $n$, inclusive, using the random module.
• Prompts the user to guess that integer. If the guess is not a positive integer, the program should prompt the user again.
  • If the guess is smaller than that integer, the program should output Too small! and prompt the user again.
  • If the guess is larger than that integer, the program should output Too large! and prompt the user again.
  • If the guess is the same as that integer, the program should output Just right! and exit.

These are the steps to solve this problem:

1. Import the random library to be abble to use the randint method to choose a number between 1 and the level given by user.
2. While the level is not a integer higher than 0 (zero) the user will be prompted to input a new number.
3. After condition is met (level is a integer higher than zero) we exit the while loop and the program will set a random number between 1 and the level given by the user.
4. Then the program asks the user to gues the number while the user has not correctly guessed the number he will be asked to input another number.

import random

while True:
    try:
        level = int(input("Level: "))
        if level > 0:
            break
    except:
        pass

randomNumber = random.randint(1, level)

while True:
    try:
        guess = int(input("Guess: "))

        if guess < randomNumber:
            print("Too small!")
        elif guess > randomNumber:
            print("Too large!")
        else:
            print("Just right!")
            break
    except:
        pass

GitHub repository

Little Professor

In this problem we will implement a program that:

• Prompts the user for a level, $n$. If the user does not input 1, 2, or 3, the program should prompt again.
• Randomly generates ten (10) math problems formatted as X + Y = , wherein each of X and Y is a non-negative integer with $n$ digits. No need to support operations other than addition (+).
• Prompts the user to solve each of those problems. If an answer is not correct (or not even a number), the program should output EEE and prompt the user again, allowing the user up to three tries in total for that problem. If the user has still not answered correctly after three tries, the program should output the correct answer.
• The program should ultimately output the user’s score: the number of correct answers out of 10.

These are the steps to solve this problem:

1. Import the random library to be abble to use the randint method to generate a random number in the function generate_integer according to user’s level choice.
2. The function get_level keeps asking a lavel for the user while it is not betwen 1 and 3.
3. In the main function we set some variables:
   • the level variable to get the user’s level choice by calling the get_level function.
   • errors to count how many times the user gave a wrong answer for the same expression.
   • totalErrors to count how many questions user gave the wrong answer.
4. In the for loop we set two variable to give a random number for x and y accordding to user’s level choice by calling the generate_integer function.
5. In try we ask user tp input the value for a given expression, if user inputs the wrong value we will raise ValueError.

import random

def main():
    level = get_level()
    errors = 0
    totalErrors = 0

    for _ in range(10):
        x = generate_integer(level)
        y = generate_integer(level)

        while True:
            try:
                answer = int(input(f"{x} + {y} = "))
                if answer == (x + y):
                    break
                else:
                    raise ValueError

            except ValueError:
                errors += 1
                if errors < 3:
                    print("EEE")
                    pass
                else:
                    print("EEE")
                    totalErrors += 1
                    print((f"{x} + {y} = {x + y}"))
                    break

    print(f"Score: {10 - totalErrors}")

def get_level():
    while True:
        try:
            level = int(input("Level: "))
            if level >= 1 and level <=3:
                return level
        except:
            pass

def generate_integer(level):
    match level:
        case 1:
            return random.randint(0, 9)
        case 2:
            return random.randint(10, 99)
        case 3:
            return random.randint(100, 999)

if __name__ == "__main__":
    main()

GitHub repository

Bitcoin Price Index

In this problem we will implement a program that:

• Expects the user to specify as a command-line argument the number of Bitcoins, $n$, that they would like to buy. If that argument cannot be converted to a float, the program should exit via sys.exit with an error message.
• Queries the API for the CoinDesk Bitcoin Price Index at https://api.coindesk.com/v1/bpi/currentprice.json, which returns a JSON object, among whose nested keys is the current price of Bitcoin as a float. Be sure to catch any exceptions, as with code like:

import requests

try:
    ...
except requests.RequestException:
    ...

• Outputs the current cost of $n$ Bitcoins in USD to four decimal places, using , as a thousands separator.

First we need to install the requests library. On the command prompt we do:

pip install requests

These are the steps to solve this problem:

1. Import the json library, the request library and the sys library.
2. In the main function we use the try to verify if the number of arguments given by the user is other than 2, otherwise it exits the program with the message Missing command-line argument.
3. If the previous statement is false we check if the value in the second position is a float, we do this by calling the isFloat function. Its sole purpose is to verify if the value is a float or not. If not it raises a expetion returning False and exiting the program with message Command-line argument is not a number.
4. If the conditions to trigger the exit the program is not activated we proceed with the request for the value of Bitcoin in USD and printing it to the user.

import json
import requests
import sys

def main():
    try:
        if len(sys.argv) != 2:
            sys.exit("Missing command-line argument")
        elif isFloat(sys.argv[1]) == False:
            sys.exit("Command-line argument is not a number")

        response = requests.get("https://api.coindesk.com/v1/bpi/currentprice.json")

        jsonResponse = response.json()
        quantity = float(sys.argv[1])
        btcPrice = jsonResponse["bpi"]["USD"]["rate_float"]

        amount = quantity * btcPrice
        print(f"${amount:,.4f}")

    except requests.RequestException:
        pass

def isFloat(string):
    try:
        float(string)
        return True
    except ValueError:
        return False

main()

GitHub repository

This is all for week four - Libraries, set of problems of CS50’s Introduction to Programming with Python course.