PEP: 3111 Title: Simple input built-in in Python 3000 Version:
$Revision$ Last-Modified: $Date$ Author: Andre Roberge <andre.roberge at
gmail.com> Status: Final Type: Standards Track Content-Type: text/x-rst
Created: 13-Sep-2006 Python-Version: 3.0 Post-History: 22-Dec-2006

Abstract

Input and output are core features of computer programs. Currently,
Python provides a simple means of output through the print keyword and
two simple means of interactive input through the input() and
raw_input() built-in functions.

Python 3.0 will introduce various incompatible changes with previous
Python versions (PEP 3100). Among the proposed changes, print will
become a built-in function, print(), while input() and raw_input() would
be removed completely from the built-in namespace, requiring importing
some module to provide even the most basic input capability.

This PEP proposes that Python 3.0 retains some simple interactive user
input capability, equivalent to raw_input(), within the built-in
namespace.

It was accepted by the BDFL in December 2006[1].

Motivation

With its easy readability and its support for many programming styles
(e.g. procedural, object-oriented, etc.) among others, Python is perhaps
the best computer language to use in introductory programming classes.
Simple programs often need to provide information to the user (output)
and to obtain information from the user (interactive input). Any
computer language intended to be used in an educational setting should
provide straightforward methods for both output and interactive input.

The current proposals for Python 3.0 <3100> include a simple output
pathway via a built-in function named print(), but a more complicated
method for input [e.g. via sys.stdin.readline()], one that requires
importing an external module. Current versions of Python (pre-3.0)
include raw_input() as a built-in function. With the availability of
such a function, programs that require simple input/output can be
written from day one, without requiring discussions of importing
modules, streams, etc.

Rationale

Current built-in functions, like input() and raw_input(), are found to
be extremely useful in traditional teaching settings. (For more details,
see[2] and the discussion that followed.) While the BDFL has clearly
stated[3] that input() was not to be kept in Python 3000, he has also
stated that he was not against revising the decision of killing
raw_input().

raw_input() provides a simple mean to ask a question and obtain a
response from a user. The proposed plans for Python 3.0 would require
the replacement of the single statement:

    name = raw_input("What is your name?")

by the more complicated:

    import sys
    print("What is your name?")
    same = sys.stdin.readline()

However, from the point of view of many Python beginners and educators,
the use of sys.stdin.readline() presents the following problems:

1. Compared to the name "raw_input", the name "sys.stdin.readline()" is
clunky and inelegant.

2. The names "sys" and "stdin" have no meaning for most beginners, who
are mainly interested in what the function does, and not where in the
package structure it is located. The lack of meaning also makes it
difficult to remember: is it "sys.stdin.readline()", or "
stdin.sys.readline()"? To a programming novice, there is not any obvious
reason to prefer one over the other. In contrast, functions simple and
direct names like print, input, and raw_input, and open are easier to
remember.

3. The use of "." notation is unmotivated and confusing to many
beginners. For example, it may lead some beginners to think "." is a
standard character that could be used in any identifier.

4. There is an asymmetry with the print function: why is print not
called sys.stdout.print()?

Specification

The existing raw_input() function will be renamed to input().

The Python 2 to 3 conversion tool will replace calls to input() with
eval(input()) and raw_input() with input().

Naming Discussion

With input() effectively removed from the language, the name raw_input()
makes much less sense and alternatives should be considered. The various
possibilities mentioned in various forums include:

    ask()
    ask_user()
    get_string()
    input()  # initially rejected by BDFL, later accepted
    prompt()
    read()
    user_input()
    get_response()

While it was initially rejected by the BDFL, it has been suggested that
the most direct solution would be to rename "raw_input" to "input" in
Python 3000. The main objection is that Python 2.x already has a
function named "input", and, even though it is not going to be included
in Python 3000, having a built-in function with the same name but
different semantics may confuse programmers migrating from 2.x to 3000.
Certainly, this is no problem for beginners, and the scope of the
problem is unclear for more experienced programmers, since raw_input(),
while popular with many, is not in universal use. In this instance, the
good it does for beginners could be seen to outweigh the harm it does to
experienced programmers -although it could cause confusion for people
reading older books or tutorials.

The rationale for accepting the renaming can be found here[4].

References

Copyright

This document has been placed in the public domain.

[1] BDFL acceptance of the PEP
https://mail.python.org/pipermail/python-3000/2006-December/005257.html

[2] The fate of raw_input() in Python 3000
https://mail.python.org/pipermail/edu-sig/2006-September/006967.html

[3] Educational aspects of Python 3000
https://mail.python.org/pipermail/python-3000/2006-September/003589.html

[4] Rationale for going with the straight renaming
https://mail.python.org/pipermail/python-3000/2006-December/005249.html