Guido on python3 for beginners

INADA Naoki songofacandy at
Thu Feb 18 03:00:32 EST 2016

In Python 3, I don't required to teach followings to newbies.

1. Don't do `class Foo:`, do `class Foo(object):`.
2. Don't do `isinstance(x, int)`, do `isinstance(x, (int, long))`.
3. Don't return non-ASCII string from `__repr__`, otherwise UnicodeError
   happens in logging and you will lost your important log.
4. Use %r instead of %s in logging to avoid UnicodeError when __str__
returns non ASCII strings.

I think there are many pitfalls fixed in Python 3 other than above.
Python 3 is far easier to teach and review code than Python 2.

On Thu, Feb 18, 2016 at 4:27 PM, Chris Angelico <rosuav at> wrote:

> On Thu, Feb 18, 2016 at 5:47 PM, Steven D'Aprano
> <steve+comp.lang.python at> wrote:
> > There are more features in Python 3, so in that trivial sense of "more to
> > learn", I suppose that it is objectively correct that it is harder to
> learn
> > than Python 2. But I don't think the learning curve is any steeper. If
> > anything, the learning curve is ever-so-slightly less steep.
> Let's see... changes in Py3.
> 1) Division of two integers now yields a float instead of flooring.
> For someone fresh to programming, that's a Py3 advantage, although it
> can cause surprises elsewhere. But since 1.0==1, it's not going to be
> a problem for a new programmer. Advantage: Py3.
> 2) Strings are Unicode text, and files etc may need to have their
> encodings declared. Definitely causes some issues in ASCII-only
> situations, where a lot of other languages (notably including PHP, for
> the people building web sites) let you be sloppy. Advantage: Py3 if
> you speak any language other than English; otherwise Py2 in the very
> short term, neither in the medium term, and most definitely Py3 in the
> long term (no more "funny characters break my program" errors long
> after deployment).
> 3) Laziness. When you explain to someone what the range() function
> does, Py2 makes a list, but Py3 makes... a range. It doesn't really
> answer the question at all. When you ask Py2 for a dictionary's
> keys/values, you get a list; Py3 gives you a thing that mostly acts
> like a list, only it isn't. If you map a function over a list, you get
> back a lazy thing that will eventually call that function. Py2 often
> has less levels of indirection, ergo less things to try to explain.
> Advantage: Py2; the benefits (lower memory usage, etc) aren't
> significant to new users.
> 4) Exception chaining. You get more information when errors cascade.
> Advantage: Py3, easily and without any question.
> 5) print statement/function. Py3 forces you to put parentheses on it,
> which is no different from C's printf() or Pike's write() or any
> number of other languages where console I/O needs no language support.
> Maybe a tiny TINY advantage to Py2 in the short term, but as soon as
> you introduce the less basic features, keyword arguments are way
> better than the magic syntax the statement needs. (Also, trying to
> explain the interaction between the print statement's "soft space" and
> other console I/O is not easy.) By the time you've really learned the
> language, the advantage belongs to Py3.
> 6) The fact that the name "python" may not invoke the interpreter you
> want. Advantage: Py2, if any; there'll be times when they're on par,
> but Py3 never comes out ahead.
> 7) Whether or not the interpreter comes pre-installed on your system.
> As of a few years ago, that was a clear advantage to Py2 (most systems
> would ship with both, or neither, or Py2 only), but that's shifting.
> It's only a small difference, though; on Windows, you generally get
> nothing, and on any system with a decent package manager, you should
> be able to request either version with ease.
> It's actually a pretty tough call. Most of the Py3 advantages aren't
> for the absolute beginner; it's not easier to write "Hello, world" in
> Py3, and aside from the change to integer division, most of the
> changes won't benefit small-to-medium scripts either. The biggest
> advantage (Unicode by default) really only shows itself by sparing you
> hassles later on - it's not going to make your life easier in the
> short term, ergo it's not going to make the language easier to learn.
> Py3 isn't so much easier as _better_. There are specific situations
> where it's massively better, but for the most part, they're about on
> par.
> ChrisA
> --

INADA Naoki  <songofacandy at>

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