Riobard Zhan schrieb:
On 5-Feb-09, at 7:31 AM, Steven D'Aprano wrote:
Riobard Zhan wrote:
Pascal uses colons, but not for the exact same purpose as Python.
Both languages use colons in similar ways to it's use in English. In
particular, Python uses colons as a break between clauses: larger
than a comma, smaller than a period.
Pascal is my first language. It has been some years ago, so I cannot
remember the detail now. I checked wikipedia and did not find colons
are used after if's. Not sure if you mean declarations? If so, I don't
think that is what we are discussing here; Java and C also use colons
in switch/case statements. AFAIK, Python is quite unique in requiring
trailing colons after if's, for's, and function/class definitions.
Python is also quite unique in using indentation to delimit blocks, so I'm not sure what point you're trying to make.
I'm sorry you dislike colons, but I like them.
Yes I agree with you that many people like colons. What bothers me is
that some people dislike them, but not given the choice to avoid them.
We don't like semicolons in Python, but what would stop a hard-core C
users to end every statement with a semicolon? They have the choice.
And I would also argue that many of those like colons not because they
really feel colons improve readability, but that they have get used to
colons in the first place. You like colons, I don't. How do you know
another Python user will like them or not? By making trailing colons
OPTIONAL, we can probably have the chance to field test. If people
really think colons improve readability that much, they can still use
them, just like we feel semicolons are line noise and void them if
possible, even though we CAN use them. I don't think we will ever lose
anything to make colons optional.
By making colon syntax flexible, we also lose a consistent look and feel of the language. 
I think it's a good indicator for optional syntax if you can formulate new rules for PEP 8 that state when to use it. In the case of colons, you'd have to either forbid or mandate them; I'd be at a loss to find another consistent rule. So, making them optional is pointless; we should either keep them or remove them. And removing is out of the question.
Applying that indicator to semicolons, there is a clear rule in PEP 8 that states when to use them: to separate two statements on one line.
I don't think it would lead to any problems, but I think it would
make Python less elegant.
I think omitting colons makes Python more elegant--more uniform, less
clutter. It's an itch every time I see a piece of Ruby code with lots
of def's and if's without trailing colons ...
That's your prerogative. However, the only person around here whose itches alone, in the face of a wall of disagreeing users, can lead to a change in the language, is Guido.
 Yes, I have read all those remarks about semicolons. What you all fail to recognize is that the majority of Python users like the colons, and wouldn't program without them. You can call it habit if you can't understand that it fits their thinking process, that's all the same: the colon won't just go away, just because it's made optional. Therefore, consistency is lost, not gained.
-- Thus spake the Lord: Thou shalt indent with four spaces. No more, no less. Four shall be the number of spaces thou shalt indent, and the number of thy indenting shall be four. Eight shalt thou not indent, nor either indent thou two, excepting that thou then proceed to four. Tabs are right out.