Learning Objectives

In this challenge we are going to focus on accessing a text file in Python to read the content of the file line by line.

Challenge

Your first challenge consists of writing a Python script that will read the following text file, one line at a time and display the content of each line on screen.

My Playlist.txt

To read the content of a text file line by line we are going to use a for loop that will loop through and extract each line of the text file one at a time. It will stop looping only once the it will have reached the last line.

Check this animation that explains this process:

When the text file uses a CSV format (Comma Separtred Values), each line contains several values separated using a special character, often a comma or a semi-colon. In this case we can use the split() method to extract each value of each line and store them in a list.

Check this animation that explains this process further:

Solution

The solutions below contains 5 main steps:

1. Step 1: Open the text file using the open() function. This function takes two parameters: The name of the file (e.g. “playlist.txt”) and the access mode. In our case we are opening the file in read-only mode: “r”.
2. Read through the file one line at a time using a for loop.
3. Split the line into an array. This is because in this file each value is separated with a semi-column. By splitting the line we can then easily access each value (field) individually.
4. Output the content of each field using the print method.
5. Once the for loop is completed, close the file using the close() method.

Main Access Modes when opening a file with the open() function.

Your Challenge

In most of your Python programs you will want to interact with the end-user by asking questions and retrieving user inputs.

To do so you can use the input() function: e.g.

username=input("What is your username?")

Sometimes you will need to retrieve numbers. Whole numbers (numbers with no decimal place) are called integers. To use them as integers you will need to convert the user input into an integer using the int() function. e.g.

age=int(input("What is your age?"))

This line of code would work fine as long as the user enters an integer. If, by mistake, they enter letters or punctuation signs, the conversion into an integer will fail and generate an exception (error) and the program would stop running.

To validate the user entry and ensure that is a number it is possible to catch this exception when it occurs using the try…except….else block as follows:

try:
    value=int(input("Type a number:"))
except ValueError:
    print("This is not a whole number.")

See how we can use this approach to define our own function (called inputNumber()) to ask for a number. This new function can then be used instead of an input() function whenever we expect the user to enter a whole number. This function uses the try…except….else block within a while loop so that it keeps asking the user to enter a number till the user gets it right.

Final Code:

def inputNumber(message):
  while True:
    try:
       userInput = int(input(message))       
    except ValueError:
       print("Not an integer! Try again.")
       continue
    else:
       return userInput 
       break 
     

#MAIN PROGRAM STARTS HERE:
age = inputNumber("How old are you?")

The aim of this blog post is to create a countdown timer that will display the numbers on screen using a 7-segment display. A lot of electronic devices use this approach to display numbers on a LED or LCD screen. (Watch, alarm clock, calculator etc.)

First we need to investigate how the 7-segment display works. You will find this page quite useful.

Typically 7-segment displays consist of seven individual coloured LED’s (called the segments). Each segment can be turned on or off to create a unique pattern/combination. Each segment is identified using a letter between A to G as follows:

The following truth table shows which segments need to be on to display the digits from 0 to 9:

Digit	A	B	C	D	E	F	G
	1	1	1	1	1	1	0
	0	1	1	0	0	0	0
	1	1	0	1	1	0	1
	1	1	1	1	0	0	1
	0	1	1	0	0	1	1
	1	0	1	1	0	1	1
	1	0	1	1	1	1	1
	1	1	1	0	0	0	0
	1	1	1	1	1	1	1
	1	1	1	1	0	1	1

Your Challenge

The code below is used to display a countdown timer counting from 5 to 0 and using the 7-segment approach to display the numbers.

Your challenge consists of using the truth table given in this post to start your countdown from 9 (instead of 5).

Challenge #2:

Start with the following message “Hello” (HELLO)