Now we know enough about Python for creating a program that is actually

useful. Awesome!

In this tutorial we'll write a program that reads questions and answers

in a text file and asks them. For example, this file would make the

program ask what "text displaying function" and "text asking function"

are:

This might seem useless to you right now, but a program like this can

actually be really useful for learning different kinds of things. I

originally wrote a program like this to study words of a foreign

language, but then I realized that I could study pretty much anything

with it.

But there are many things the program needs to do and writing it seems

really difficult and complicated! How the heck can we do this?

Our program will need to do several different things:

1. Read the questions from a file.

2. Ask the questions.

3. Print statistics about how many questions were answered correctly

and how many wrong.

Now everything seems much easier. We know how to do each of these steps

one by one, but doing it all at once would be difficult. In situations

like this **it's important to [define

functions](defining-functions.md)**. We are going to write a

`read_questions` function, an `ask_questions` function and a `stats`

function.

Let's start with the function that reads the question file:

def read_questions(filename):

answers = {}

with open(questionfile, 'r') as f:

for line in f:

line = line.strip()

if line: # ignore empty lines

question, answer = line.split('=')

answers[question.strip()] = answer.strip()

return answers

At this point it's best to try out the function to see how it works. You

need to create a `questions.txt` file like the one in the beginning of

this tutorial if you didn't create it already.

**TODO:** Instructions for using the -i switch.

>>> read_questions('questions.txt')

{'text displaying function': 'print', 'text asking function': 'input'}

If your function doesn't work correctly it doesn't matter, and fixing

the problem is easy because the function is so short. This is one of the

reasons why we write functions.

Next we'll write the rest of the functions the same way, first writing

and then testing and fixing. Here are my versions of them:

def ask_questions(answers):

correct = []

wrong = []

for question, answer in answers.items():

if input(question + ' = ').strip() == answer:

print("Correct!")

correct.append(question)

else:

print("Wrong! The correct answer is %s." % answer)

wrong.append(question)

return (correct, wrong)

def stats(correct, wrong, answers):

print("\n**** STATS ****\n")

print("You answered", len(correct), "questions correctly and",

len(wrong), "questions wrong.")

if wrong:

print("These would have been the correct answers:")

for question in wrong:

print(' ', question, '=', answers[question])

Let's try them out.

>>> answers = read_questions('questions.txt')

>>> correct, wrong = ask_questions(answers)

text displaying function = print

Correct!

text asking function = elif

Wrong! The correct answer is input.

>>> correct

['text displaying function']

>>> wrong

['text asking function']

>>> stats(correct, wrong, answers)

*** STATS ***

You answered 1 questions right and 1 questions wrong.

These would have been the correct answers:

text asking function = input

Everything is working! Now we just need something that runs everything

because we don't want to type this out on the `>>>` prompt every time.

You might have noticed that the stats function printed `1 questions`

instead of `1 question`, and it looks a bit weird. You can modify the

`print_stats` function to fix this if you want to.

The last function in a program like this is usually called `main` and it

runs the program using other functions. Our main function consists of

mostly the same pieces of code that we just tried out on the `>>>`

prompt.

def main():

filename = input("Name of the question file: ")

answers = read_questions(filename)

correct, wrong = ask_questions(answers)

stats(correct, wrong, answers)

The last thing we need to add is these two lines:

if __name__ == '__main__':

main()

The `__name__` variable is set differently depending on how we run the

file, and **it's `'__main__'` when we run the file directly instead of

importing**. So if we run the file normally it asks us the words, and if

we import it instead we can still run the functions one by one. If you

want to know more about `__name__` just make a file that prints it and

run it in different ways.

Now the whole program looks like this:

def read_questions(filename):

answers = {}

with open(questionfile, 'r') as f:

for line in f:

line = line.strip()

if line: # ignore empty lines

question, answer = line.split('=')

answers[question.strip()] = answer.strip()

return answers

def ask_questions(answers):

correct = []

wrong = []

for question, answer in answers.items():

if input('%s = ' % question).strip() == answer:

print("Correct!")

correct.append(question)

else:

print("Wrong! The correct answer is %s." % answer)

wrong.append(question)

return (correct, wrong)

def stats(correct, wrong, answers):

print("\n**** STATS ****\n")

print("You answered", len(correct), "questions correctly and",

len(wrong), "questions wrong.")

if wrong:

print("These would have been the correct answers:")

for question in wrong:

print(' ', question, '=', answers[question])

def main():

filename = input("Name of the question file: ")

answers = read_questions(filename)

correct, wrong = ask_questions(answers)

stats(correct, wrong, answers)

if __name__ == '__main__':

main()

This is just the beginning. Now [you can](../LICENSE) take your word

asking program and make your own version of it that suits **your**

needs. Then you can share it with your friends so they will find it

useful as well.

- Make multiple functions when your program needs to do multiple things.

Each function should do one thing.

- Try out the functions on the `>>>` prompt when you want to check if

they work correctly.

- `__name__` is `'__main__'` when the program is supposed to run, and

something else when it's imported.

You may use this tutorial freely at your own risk. See

[LICENSE](../LICENSE).

[Previous](defining-functions.md) | [Next](what-is-true.md) |

[List of contents](../README.md#basics)