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Re: Language design

Date 2013-09-11 22:41 +0200
From Markus Rother <python@markusrother.de>
Subject Re: Language design
References <522eb795$0$29999$c3e8da3$5496439d@news.astraweb.com>
Newsgroups comp.lang.python
Message-ID <mailman.266.1378933023.5461.python-list@python.org> (permalink)

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Hello all,

Thanks for this thread.  Here are my two cents...

On 10.09.2013 08:09, Steven D'Aprano wrote:
> What design mistakes, traps or gotchas do you think Python has? Gotchas 
> are not necessarily a bad thing, there may be good reasons for it, but 
> they're surprising.

    """
    1. Occasionally, one encounters a strange idiom.  Syntactically
    legal and consistent, though:

    >>> +4++4
    8
    >>> -4+-4
    -8
    >>> -4-+4
    -8


    2. Reduce removed from standard library.  That is a big fail, in
    my opinion.


    3. The default return value of methods is None instead of self.
    If it was self, it would be possible to chain method calls (which
    is called a cascade in smalltalk).


    >>> lst = []
    >>> lst.append(1).append(2).append(3) ## FAIL
    Traceback (most recent call last):
    ...
    AttributeError: 'NoneType' object has no attribute 'append'


    Instead, this works:


    >>> class Coll(list):
    ...
    ...     def add(self, e):
    ...         self.append(e)
    ...         return self
    ...
    >>> lst = Coll()
    >>> lst.add(1).add(2).add(3) ## OK
    [1, 2, 3]


    A very practical use case is, that the return value of None makes
    all of these methods unusable for reduce.


    >>> from functools import reduce
    ...
    >>> many = [{1: 'a'}, {2: 'b'}, {3: 'c'}]
    ...
    >>> reduce(lambda d, other : d.update(other), many, {}) ## FAIL
    Traceback (most recent call last):
    ...
    AttributeError: 'NoneType' object has no attribute 'update'


    Again, one would have to define an update function with an
    explicit return value.

    >>> many = [{1: 'a'}, {2: 'b'}, {3: 'c'}]
    ...
    >>> def fn(d, other):
    ...     d.update(other)
    ...     return d
    ...
    >>> reduce(fn, many, {}) ## OK
    {1: 'a', 2: 'b', 3: 'c'}


    4. As has been mentioned already, some built-in functions do magic
    stuff behind the scenes:


    >>> () == []
    False


    But:


    >>> bool(().__eq__([]))
    True


    Because:


    >>> ().__eq__([])
    NotImplemented


    which yields True when cast to boolean.
    """

Greets,
Markus

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Thread

Language design Steven D'Aprano <steve@pearwood.info> - 2013-09-10 06:09 +0000
  Re: Language design diverman <pavel@schon.cz> - 2013-09-09 23:59 -0700
  Re: Language design Ben Finney <ben+python@benfinney.id.au> - 2013-09-10 17:07 +1000
    Re: Language design Nobody <nobody@nowhere.com> - 2013-09-11 01:03 +0100
      Re: Language design Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-09-11 00:53 +0000
        Re: Language design Nobody <nobody@nowhere.com> - 2013-09-12 18:23 +0100
  Re: Language design Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-09-10 09:58 +0200
  Re: Language design Chris Angelico <rosuav@gmail.com> - 2013-09-10 20:20 +1000
  Re: Language design Chris Rebert <clp2@rebertia.com> - 2013-09-10 18:46 -0700
  Re: Language design Chris Angelico <rosuav@gmail.com> - 2013-09-11 14:21 +1000
  Re: Language design Burak Arslan <burak.arslan@arskom.com.tr> - 2013-09-11 13:38 +0300
    Re: Language design Neil Cerutti <neilc@norwich.edu> - 2013-09-11 14:32 +0000
      Re: Language design Chris Angelico <rosuav@gmail.com> - 2013-09-12 00:46 +1000
  Re: Language design Wayne Werner <wayne@waynewerner.com> - 2013-09-11 06:42 -0500
  Re: Language design Dave Angel <davea@davea.name> - 2013-09-11 12:05 +0000
  Re: Language design Ethan Furman <ethan@stoneleaf.us> - 2013-09-11 07:52 -0700
  Re: Language design Burak Arslan <burak.arslan@arskom.com.tr> - 2013-09-11 18:41 +0300
  Re: Language design Markus Rother <python@markusrother.de> - 2013-09-11 22:41 +0200
    Re: Language design Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-09-11 23:40 +0000
  Re: Language design Mark Janssen <dreamingforward@gmail.com> - 2013-09-11 14:22 -0700
  Re: Language design Mark Janssen <dreamingforward@gmail.com> - 2013-09-11 14:30 -0700
    Re: Language design Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-09-11 23:40 +0000
      Re: Language design Mark Janssen <dreamingforward@gmail.com> - 2013-09-11 17:49 -0700
        Re: Language design Steven D'Aprano <steve@pearwood.info> - 2013-09-12 05:33 +0000
          Re: Language design Mark Janssen <dreamingforward@gmail.com> - 2013-09-12 20:23 -0700
            Re: Language design Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-09-13 05:08 +0000
              Re: Language design Chris Angelico <rosuav@gmail.com> - 2013-09-13 17:39 +1000
              Re: Language design Mark Janssen <dreamingforward@gmail.com> - 2013-09-14 19:37 -0700
              Re: Language design Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-09-15 09:57 +0200
      Re: Language design Terry Reedy <tjreedy@udel.edu> - 2013-09-11 21:40 -0400
      Re: Language design Chris Angelico <rosuav@gmail.com> - 2013-09-12 11:41 +1000
  Re: Language design Ethan Furman <ethan@stoneleaf.us> - 2013-09-11 14:15 -0700
  RE: Language design "Prasad, Ramit" <ramit.prasad@jpmorgan.com.dmarc.invalid> - 2013-09-11 21:56 +0000
  Re: Language design Ben Finney <ben+python@benfinney.id.au> - 2013-09-12 09:16 +1000
  Please omit false legalese footers (was: Language design) Ben Finney <ben+python@benfinney.id.au> - 2013-09-12 09:22 +1000
    Re: Please omit false legalese footers (was: Language design) Grant Edwards <invalid@invalid.invalid> - 2013-09-12 20:12 +0000
  Re: Language design Chris Angelico <rosuav@gmail.com> - 2013-09-12 09:27 +1000
  Re: Language design Ben Finney <ben+python@benfinney.id.au> - 2013-09-12 09:19 +1000
  Re: Language design Terry Reedy <tjreedy@udel.edu> - 2013-09-11 19:51 -0400
  Re: Language design Mark Janssen <dreamingforward@gmail.com> - 2013-09-11 17:25 -0700
  Re: Language design Chris Angelico <rosuav@gmail.com> - 2013-09-12 10:31 +1000
    Re: Language design Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-09-12 02:33 +0000
      Re: Language design Roy Smith <roy@panix.com> - 2013-09-11 22:43 -0400
        Re: Language design Chris Angelico <rosuav@gmail.com> - 2013-09-12 12:58 +1000
        Re: Language design Steven D'Aprano <steve@pearwood.info> - 2013-09-12 05:08 +0000
  Re: Language design Mark Janssen <dreamingforward@gmail.com> - 2013-09-11 17:34 -0700
  Re: Language design Mark Janssen <dreamingforward@gmail.com> - 2013-09-11 17:37 -0700
  Re: Language design Chris Angelico <rosuav@gmail.com> - 2013-09-12 10:40 +1000
  Re: Language design Benjamin Kaplan <benjamin.kaplan@case.edu> - 2013-09-11 17:54 -0700
  Re: Language design Ben Finney <ben+python@benfinney.id.au> - 2013-09-12 10:57 +1000
  Re: Language design Joshua Landau <joshua@landau.ws> - 2013-09-12 05:17 +0100
  Re: Please omit false legalese footers (was: Language design) Skip Montanaro <skip@pobox.com> - 2013-09-12 04:27 -0500
  Re: Please omit false legalese footers (was: Language design) Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-09-12 10:44 +0100
  Re: Language design Markus Rother <python@markusrother.de> - 2013-09-12 19:51 +0200
    Re: Language design Neil Cerutti <neilc@norwich.edu> - 2013-09-12 18:06 +0000
  Re: Language design Markus Rother <python@markusrother.de> - 2013-09-12 20:13 +0200
  Re: Language design Markus Rother <python@markusrother.de> - 2013-09-12 20:24 +0200
    Re: Language design Neil Cerutti <neilc@norwich.edu> - 2013-09-12 19:18 +0000
  Re: Language design Ethan Furman <ethan@stoneleaf.us> - 2013-09-12 11:05 -0700
  Re: Language design Ned Batchelder <ned@nedbatchelder.com> - 2013-09-12 14:37 -0400
  Re: Language design Terry Reedy <tjreedy@udel.edu> - 2013-09-12 14:46 -0400
  Re: Language design Chris Angelico <rosuav@gmail.com> - 2013-09-13 07:53 +1000
  Re: Language design Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-09-13 09:04 +0200
    Re: Language design Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-09-13 10:13 +0000
      Re: Language design Chris Angelico <rosuav@gmail.com> - 2013-09-13 21:16 +1000
      Re: Language design Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-09-13 13:28 +0200
      Re: Language design Terry Reedy <tjreedy@udel.edu> - 2013-09-13 15:32 -0400
      Re: Language design Chris Angelico <rosuav@gmail.com> - 2013-09-14 09:57 +1000
        Re: Language design Neil Cerutti <neilc@norwich.edu> - 2013-09-18 14:57 +0000
          Re: Language design Chris Angelico <rosuav@gmail.com> - 2013-09-19 01:02 +1000
            Re: Language design Neil Cerutti <neilc@norwich.edu> - 2013-09-18 15:08 +0000
              Re: Language design Chris Angelico <rosuav@gmail.com> - 2013-09-19 01:12 +1000
              Re: Language design William Ray Wing <wrw@mac.com> - 2013-09-18 12:58 -0400
                Re: Language design wxjmfauth@gmail.com - 2013-09-18 10:45 -0700
                Re: Language design Neil Cerutti <neilc@norwich.edu> - 2013-09-18 17:55 +0000
      Re: Language design Mark Janssen <dreamingforward@gmail.com> - 2013-09-13 17:28 -0700
      Re: Language design Vito De Tullio <vito.detullio@gmail.com> - 2013-09-14 07:25 +0200

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