Python was designed (was Re: Multi-threading in Python vs Java)

[Chris Angelico]

On Sat, Oct 12, 2013 at 7:10 AM, Peter Cacioppi
<peter.cacioppi at gmail.com> wrote:
> Along with "batteries included" and "we're all adults", I think Python needs a pithy phrase summarizing how well thought out it is. That is to say, the major design decisions were all carefully considered, and as a result things that might appear to be problematic are actually not barriers in practice. My suggestion for this phrase is "Guido was here".

"Designed".

You simply can't get a good clean design if you just let it grow by
itself, one feature at a time. You'll end up with something where you
can do the same sort of thing in three different ways, and they all
have slightly different names:

http://me.veekun.com/blog/2012/04/09/php-a-fractal-of-bad-design/#general

(Note, I'm not here to say that PHP is awful and Python is awesome
(they are, but I'm not here to say it). It's just that I can point to
a blog post that shows what I'm saying.)

Design is why, for instance, Python's builtin types all behave the
same way with regard to in-place mutator methods: they don't return
self. I personally happen to quite like the "return self" style, as it
allows code like this:

GTK2.MenuBar()
    ->add(GTK2.MenuItem("_File")->set_submenu(GTK2.Menu()
        ->add(menuitem("_New Tab",addtab)->add_accelerator(...))
        ->add(menuitem("Close tab",closetab)->add_accelerator(...))
        ... etc ...
    ))
    ->add(GTK2.MenuItem("_Options")->set_submenu(GTK2.Menu()
        ->add(menuitem("_Font",fontdlg))
        ... etc ...
    ))
    ... etc ...

It's a single expression (this is from Pike, semantically similar to
Python) that creates and sets up the whole menu bar. Most of Pike's
object methods will return this (aka self) if it's believed to be of
use. The Python equivalent, since the .add() method on GTK objects
returns None, is a pile of code with temporary names. But that's a
smallish point of utility against a large point of consistency;
newbies can trust that a line like:

lst = lst.sort()

will trip them up immediately (since lst is now None), rather than
surprise them later when they try to make a sorted copy of the list:

sorted_lst = lst.sort()

which, if list.sort returned self, would leave you with sorted_lst is
lst, almost certainly not what the programmer intended.

Oh, and the use of exceptions everywhere is a sign of design, too.
Something went wrong that means you can't return a plausible value?
Raise.

>>> json.loads("{")
ValueError: Expecting object: line 1 column 0 (char 0)

>>> pickle.loads(b"\x80")
EOFError

Etcetera. PHP borrows from C in having piles and piles of "was there
an error" functions; there's no consistency in naming, nor (in many
cases) in the return values. Pike generally raises exceptions, but I/O
failure usually results in a zero return and the file object's errno
attribute set; but at least they're consistent error codes.

This is design. Python has a king (Guido). It wasn't built by a
committee. Maybe you won't like some aspect of Python's design, but it
has one, it's not just sloppily slapped together.

ChrisA