Undecoratable

Decorators are one of Python's bigger success stories, and many programmers' first experience with higher-order programming. Most practiced and prolific Python programmers will find themselves making good use of them regularly.

But every feature has its limits, and here's a new one to try on for size:

>>> @x().y()
  File "<stdin>", line 1
    @x().y()
        ^
SyntaxError: invalid syntax

That's right, decoration is not an arbitrary Python expression. It doesn't matter what x and y were, or even if they were defined. You can't follow a function call with a dot. @x() works fine, @x.y() would work fine, too. But @x().y(), that's only for mad Pythonists who would take things TOO FAR.

Decorator invocations, defined at the top of the Python grammar, can only be followed by class definitions and function definitions.

Well, now we know, and now we can all say we've been there

-- Mahmoud
http://sedimental.org/
https://github.com/mahmoud
https://twitter.com/mhashemi

List Comprehension Code Golf

Ah code golf, pastime of our navelgazing alter egos. Being designed for readability and maintainability, Python doesn't always show well in this sort of sport, but occasionally we get thrown a bone. For instance, for nonzero even numbers less than 10:

>>> [x for x in range(10) if x and not x % 2]
[2, 4, 6, 8]

is equivalent to

>>> [x for x in range(10) if x if not x % 2]
[2, 4, 6, 8]

A whole character saved! Yes, a close reading of PEP 202 will show that one of the canonical examples of list comprehensions uses this pattern for... some reason.

Either way, now you know. Sally forth and do what must be done with all code golf tricks: Never, Ever Use Them For Production Code.

-- Mahmoud
http://sedimental.org/
https://github.com/mahmoud
https://twitter.com/mhashemi