Could Emacs be rewritten in Python?
tanzer at swing.co.at
Mon Apr 14 19:01:41 CEST 2003
Robin Munn <rmunn at pobox.com> wrote:
> Paul Foley <see at below.invalid> wrote:
> > I.e., write broken and fragile code just to avoid a perfectly good
> > construct that you happen to dislike for religious reasons.
> > Brilliant!
> How is try ... finally "broken and fragile code"? How is this:
> old_stdout = sys.stdout
> new_stdout = cStringIO.StringIO()
> sys.stdout = new_stdout
> sys.stdout = old_stdout
> in any way inferior to this (making up a semi-Pythonic syntax):
> with sys.stdout = cStringIO.StringIO():
> Yes, sample #2 is shorter. But it would require adding a new keyword to
> the language, which is a pretty heavy price to pay. And sample #2
> doesn't need a temporary variable -- but sample #1's temporary variable
> is a function-local variable, so speed and namespace-clutter costs are
> What I really want to know is why you would consider sample #1 "broken
> and fragile code". I can't think of any circumstances where sample #1
> would fail to achieve its desired effect. Can you?
Disclaimer: I'm not arguing for adding dynamic scopes or variable
declarations to Python <wink>.
I see three problems with try/finally for temporary rebindings of
- It is fragile for multiple rebindings unless you save all the old
values before the try.
- It is easy to forget/inadvertantly delete some restore operations in
the finally clause.
- It destroys locality of reference for the human reader. Your toy
example needs eight try/finally lines vs. three lines for the
alternative solution. For multiple rebindings, the ratio gets worse.
Christian Tanzer tanzer at swing.co.at
Glasauergasse 32 Tel: +43 1 876 62 36
A-1130 Vienna, Austria Fax: +43 1 877 66 92
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