I. Input and output

I.1 Introduction

Almost any interesting program has to get information from somewhere, and produce some sort of answers somewhere. These are called input and output. This sheet describes some of the ways Python handles input and output.

Some of the things in here require you to have done

from gasp import *

before they'll work.

I.2 Input

Here are some useful functions that ask the user a question and wait for an answer. They all expect that the user will hit Enter after typing the answer.

read_number()

Expects a number. If you type in something that isn't a number, you'll get told to try again.

read_number('Enter a number: ')

The same, but prints that message before waiting for input. It's usually better to use this version of read_number (perhaps with a different message, like 'How old are you?') so that the person using your program knows what's required.

read_string()

Expects a string. You don't need to put quotation marks around it.

read_string("What's your name? ")

Just like read_string(), but prints a message first.

read_yesorno()

Expects yes, no, y or n, in either capitals or lowercase.

read_yesorno("Would you like another game? ")

Just like read_yesorno(), but prints a message first.

I.3 Output

The main thing you need to know about output is the print statement. It can print any object:

>>> x = [1, 2, 3]  # a list,
>>> y = 'zog'      # a string,
>>> z = 99         # a number,
>>> f = repr       # a function
>>> print x, y, z, f
[1, 2, 3] zog 99 <built-in function repr>

Notice that it puts spaces between the things it prints.

If you write two print statements, one after the other, you'll see that the second starts printing on a fresh line rather than following on from the first. If that isn't what you want, put a comma at the end of the first print:

print 123,
print 456

This will print 123 456 on a single line.