Input and output

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.

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. When you enter a number, it is returned to the part of your program that called read_number.

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. It returns True when either yes or y is entered and False for no or n. A sample session in the interpreter might look like this:

>>> read_yesorno()
Yes or no? yes
True
>>> read_yesorno()
Yes or no? no
False
>>> read_yesorno()
Yes or no? What?
Please answer yes or no.
Yes or no? y
True
>>>

read_yesorno("Would you like another game? ")

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

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

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.