Python interface "sequence protocol"

Skef Iterum <[email protected]> Sun, 3 Feb 2019 01:42:14 -0800
Newsgroups gmane.comp.fonts.fontforge.devel
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Note that:

 1. (At best) this question relates to a release after the upcoming one,
    so there is no hurry.
 2. I\m using an out of date version of the docs because sub-links work.

Some of the important Python objects, including Layer and Contour, have 
what the documentation calls a "sequence protocol":

http://dmtr.org/ff.php#Layer

It's clear how this interface is supposed to work for /changing/ an 
existing element or /appending/ a new element. Contour also has 
insertPoint for adding a point in the middle of the point sequence. But 
what about the other operations? How should one reduce the number of 
contours in a layer or points in a contour? Calling del on a layer array 
element results in a segfault. Maybe that operation should throw an 
exception to avoid "holes", but the existing interface just seems 
incomplete.

On the meta-level, how does the project wish to answer questions of this 
type at present?

(fontParts, rising from RoboFont ashes, only exposes a read-only tuple 
of contours in the corresponding context, and uses methods otherwise.)

Skef


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    <p>Note that:</p>
    <ol>
      <li>(At best) this question relates to a release after the
        upcoming one, so there is no hurry. <br>
      </li>
      <li>I\m using an out of date version of the docs because sub-links
        work. <br>
      </li>
    </ol>
    <p>Some of the important Python objects, including Layer and
      Contour, have what the documentation calls a "sequence protocol":</p>
    <p><a class="moz-txt-link-freetext" href="http://dmtr.org/ff.php#Layer">http://dmtr.org/ff.php#Layer</a></p>
    <p>It's clear how this interface is supposed to work for <i>changing</i>
      an existing element or <i>appending</i> a new element. Contour
      also has <tt>insertPoint</tt> for adding a point in the middle of
      the point sequence. But what about the other operations? How
      should one reduce the number of contours in a layer or points in a
      contour? Calling <tt>del</tt> on a layer array element results in
      a segfault. Maybe that operation should throw an exception to
      avoid "holes", but the existing interface just seems incomplete. <br>
    </p>
    <p>On the meta-level, how does the project wish to answer questions
      of this type at present?<br>
    </p>
    <p>(fontParts, rising from RoboFont ashes, only exposes a read-only
      tuple of contours in the corresponding context, and uses methods
      otherwise.)</p>
    <p>Skef<br>
    </p>
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