[Python-Dev] Why can't I encode/decode base64 without importing a module?

Guido van Rossum guido at python.org
Tue Apr 23 19:24:53 CEST 2013

On Tue, Apr 23, 2013 at 9:04 AM, M.-A. Lemburg <mal at egenix.com> wrote:
> On 23.04.2013 17:47, Guido van Rossum wrote:
>> On Tue, Apr 23, 2013 at 8:22 AM, M.-A. Lemburg <mal at egenix.com> wrote:
>>> Just as reminder: we have the general purpose
>>> encode()/decode() functions in the codecs module:
>>> import codecs
>>> r13 = codecs.encode('hello world', 'rot-13')
>>> These interface directly to the codec interfaces, without
>>> enforcing type restrictions. The codec defines the supported
>>> input and output types.
>> As an implementation mechanism I see nothing wrong with this. I hope
>> the codecs module lets you introspect the input and output types of a
>> codec given by name?
> At the moment there is no standard interface to access supported
> input and output types... but then: regular Python functions or
> methods also don't provide such functionality, so no surprise
> there ;-)

Not quite the same though. Each function has its own unique behavior.
But codecs support a standard interface, *except* that the input and
output types sometimes vary.

> It's mostly a matter of specifying the supported type
> combinations in the codec documentation.
> BTW: What would be a use case where you'd want to
> programmatically access such information before calling
> the codec ?

As you know, in Python 3, most code working with bytes doesn't also
work with strings, and vice versa (except for a few cases where we've
gone out of our way to write polymorphic code -- but users rarely do
so, and any time you use a string or bytes literal you basically limit
yourself to that type).

Suppose I write a command-line utility that reads a file, runs it
through a codec, and writes the result to another file. Suppose the
name of the codec is a command-line argument (as well as the
filenames). I need to know whether to open the files in text or binary
mode based on the name of the codec.

--Guido van Rossum (python.org/~guido)

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