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 [5].

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 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.