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bug#15295: python mode slow to unusable
From: |
Michael Heerdegen |
Subject: |
bug#15295: python mode slow to unusable |
Date: |
Sat, 26 Oct 2013 13:39:21 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.3.50 (gnu/linux) |
Alex V. Koval <alex@ua2web.com> writes:
> For me this is happen as well. Emacs, starting from version 24.3 became
> so slow in Python mode that I had to tell all developers at our company
> to use version 24.2 until I sorted this out.
>
> Sit today and started trying various emacs versions, and calling
> different functions. The suggested test case from original author above,
> runs with this benchmark:
>
> (7.3956507 53 1.8788885930000063)
I profiled a bit, and, at least in this example, these two functions
seem to be extremely inefficient in combination:
(defun python-nav-beginning-of-statement ()
"Move to start of current statement."
(interactive "^")
(while (and (or (back-to-indentation) t)
(not (bobp))
(when (or
(save-excursion
(forward-line -1)
(python-info-line-ends-backslash-p))
(python-syntax-context 'string)
(python-syntax-context 'paren))
(forward-line -1))))
(point-marker))
(defun python-info-line-ends-backslash-p (&optional line-number)
"Return non-nil if current line ends with backslash.
With optional argument LINE-NUMBER, check that line instead."
(save-excursion
(save-restriction
(widen)
(when line-number
(python-util-goto-line line-number))
(while (and (not (eobp))
(goto-char (line-end-position))
(python-syntax-context 'paren)
(not (equal (char-before (point)) ?\\)))
(forward-line 1))
(when (equal (char-before) ?\\)
(point-marker)))))
They consume most of the time used. While the first function goes
backward, the second goes forward to the end in every loop cycle. This
makes the thing O(n^2), with n being the number of lines of the
expression.
I don't know Python, so I can't make any suggestions. Who can? At
least, changing the order of `or' expressions in
`python-nav-beginning-of-statement' seems to help in the example case:
(defun python-nav-beginning-of-statement ()
"Move to start of current statement."
(interactive "^")
(while (and (or (back-to-indentation) t)
(not (bobp))
(when (or
(python-syntax-context 'string)
(python-syntax-context 'paren)
(save-excursion
(forward-line -1)
(python-info-line-ends-backslash-p)))
(forward-line -1))))
(point-marker))
It's also not efficient how often `syntax-ppss' is called all the time.
Regards,
Michael.