On: Migrating to Python 3 with pleasure

[Doxin]

    return dict(x, **{'fo'+'o': 'bar'}, **y)

The new syntax is some mild syntactic sugar. (Which isn't a bad thing IMO)

[Sean1708 → Doxin]

Did you try your example? It never worked in Python2 and it doesn't work in Python3 by design.

  Python 2.7.12 (default, Dec  4 2017, 14:50:18) 
  [GCC 5.4.0 20160609] on linux2
  Type "help", "copyright", "credits" or "license" for more information.
  >>> x = {'foo': 5, 'bar': 6}
  >>> y = {'foo': 7, 'baz': 9}
  >>> dict(x, **{'fo'+'o': 'bar'}, **y)
    File "<stdin>", line 1
      dict(x, **{'fo'+'o': 'bar'}, **y)
                                 ^
  SyntaxError: invalid syntax

  Python 3.5.2 (default, Nov 23 2017, 16:37:01) 
  [GCC 5.4.0 20160609] on linux
  Type "help", "copyright", "credits" or "license" for more information.
  >>> x = {'foo': 5, 'bar': 6}
  >>> y = {'foo': 7, 'baz': 9}
  >>> dict(x, **{'fo'+'o': 'bar'}, **y)
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
  TypeError: type object got multiple values for keyword argument 'foo'
  >>> {**x, 'fo'+'o': 'bar', **y}
  {'foo': 7, 'baz': 9, 'bar': 6}

[kamaal → Doxin]

This is the most unreadable code I've seen so far.

Just skip all this and use Perl instead. You can write far more idiomatic, succinct readable code in Perl than you can in Python.

The whole point of Python is to not write code this way.

[vgy7ujm → kamaal]

This is what I have been saying for a long time. Readability in Python is an illusion.

[orf → Doxin]

On the face of it, sure, but really it's some new bytecode that gets rid of the limitations of using kwargs like that, namely it's slow, impossible to really optimize and doesn't support duplicate keys.

[masklinn → Doxin]

Except that does not necessarily work with non-string keys (it'd depend on version and implementation IIRC).

The expanded unpacking works in all cases.

[singingfish → Doxin]

And people say perl is unreadable ;)