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Sign up| 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\ [1]_. 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 [1]_ 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 | |
| ========== | |
| .. [1] PEP 3100, Miscellaneous Python 3.0 Plans, Kuchling, Cannon | |
| http://www.python.org/dev/peps/pep-3100/ | |
| .. [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 | |
| .. [5] BDFL acceptance of the PEP | |
| https://mail.python.org/pipermail/python-3000/2006-December/005257.html | |
| Copyright | |
| ========= | |
| This document has been placed in the public domain. | |