[Python-Dev] Suggesting '.' decorators (PEP318) (original) (raw)

Kevin J. Butler python-kbutler at sabaydi.com
Sat Aug 7 06:55:35 CEST 2004

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Many people wrote: > Lots of options

I haven't seen this mentioned, so I'm going to throw in my suggestion.

The following makes sense to me, uses previously invalid syntax, and uses the '.' punctuation in a way similar to existing/proposed usage:

   def longMethodNameForEffect(longArgumentOne=None,
                               longArgumentTwo=42):
       .staticmethod
       .funcattrs(grammar="'@' dotted_name [ '(' [arglist] ')' ]",
                  status="experimental", author="BDFL")
       """
       asdfasdf
       """
       raise NotYetImplemented

If we want to allow one-liner decorators (questionable to me):

   def myMethod(self): .staticmethod
       raise NotYetImplemented

Advantages/disadvantages of positioning at start of block:

• Unambiguous "target" for decorators, matches Python's precedents for indentation and modify-what-came-before

• Decorators won't get lost in long argument lists (they are indented differently in Guido's preferred formatting, and are separated by the smiley in the all-args-on-individual-lines formatting)

• Separate from def syntax (to keep def the same avoiding breakage)

0 Perhaps decorators should be allowed before or after the docstring. If you have to choose, I'd choose making it before the docstring.

• No extra cut-and-paste issues, no extra indentation level.

• No smileys. (Does that get a :) or a ]: ?)

Advantages/disadvantages of .decorators:

• Will not be silently ignored (doesn't use currently legal syntax)

• Simple for simple decorators, supports complex decorators as cleanly as possible

• Less ugly (YMMV). Doesn't feel like executable line noise (to 1 out of 1 pythonistas polled...)

• No new punctuation or keywords (avoids breaking Leo/IPython/existing code)

• Really nice syntax for assigning attributes, if desired (Not sure I like this overloading, but it /looks/ good)

   def func():
       .author = "Kevin Butler"
       pass

+/0 Syntax obvious visually (Someone will complain that the leading period gets lost - that person should switch to a fixed-width font, as used when coding. <.5 wink>) Easy to highlight.

0 Although it is a punctuation-based syntax, it is compatible with existing/proposed '.' usage ('.' can mean subordination to a containing construct like 'with', and passing the implicit "func" argument is analogous to passing "self")

0 Compatible with some future "with ...:" syntax, as decorators must immediately follow a 'def ...:' (or possibly a 'class ...:'), so if there is a 'with ...:' what follows cannot be a decorator.

• Minor extension to use of '.'

• Some people may have too much dust on their monitors

Misc items from the PEP applied to .decorators:

• One decorator per line

• Could use ".doc()" or ".doc = " as a docstring alternative

?+ Compile time (? as much as the @ syntax is?)

• Works in interactive mode

Public or private feedback appreciated, I will summarize private feedback to the list.

kb

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