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How to select all the edges through the YZ plane with a python script ?

enter image description here

update

I know this script which do it for faces but I don't know the equivalent for edges :

import bpy, bmesh

me = bpy.context.object.data

bm = bmesh.new()
bm.from_mesh(me)

for face in bm.faces:

    center = face.calc_center_median()

    if center.x == 0:

        face.select_set(True)

bm.to_mesh(me)
bm.free()
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    $\begingroup$ Not sure why the question got a downvote, but I suspect because it is more like a request for script without any signs of an attempt by you to research how such a script might be put together. $\endgroup$ Commented Mar 26, 2015 at 9:47
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    $\begingroup$ how would you decide the x component of the plane? Remember scripts don't have eyes, like ours that let us immediately say ' oh of course, that vertex and edge lies on the plane '. Would your script need to find this plane autonomously or would you be giving it a helping hand by providing a pre-selection first $\endgroup$ Commented Mar 26, 2015 at 10:24
  • $\begingroup$ the x component of the plan is zero, it's at the origin. $\endgroup$ Commented Mar 26, 2015 at 10:36
  • $\begingroup$ just select the verts instead and automatically the edges are selected $\endgroup$ Commented Mar 26, 2015 at 10:53

1 Answer 1

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Armed with the extra information consider:

import bpy, bmesh

me = bpy.context.object.data

bm = bmesh.new()
bm.from_mesh(me)

EPSILON = 1.0e-5

for vert in bm.verts:
    if -EPSILON <= vert.co.x <= EPSILON:
        vert.select = True

bm.to_mesh(me)
bm.free()

Some clarification perhaps:

EPSILON represents a value that is close to 0. If you've ever inspected coordinates closely in Blender you will find a cut off point maybe at around 6 or 7 digits after the decimal where you start to encounter artefacts in the representation of that float. Because 0 and 0.0000012312423 are not the same number you can't simply do a check for equality with 0, instead you might check is the x component within EPSILON tolerance.

Here I make the significant digit 5 places after the decimal point, from practical experience i've found this to be sufficient.

>>> 1.0e-5 == 0.00001
True

The above will select just the vertices, from that point selecting the edges shouldn't be too difficult. Here's a quick implementation

import bpy, bmesh

me = bpy.context.object.data

bm = bmesh.new()
bm.from_mesh(me)

EPSILON = 1.0e-5
for vert in bm.verts:
    if -EPSILON <= vert.co.x <= EPSILON:
        vert.select = True

for edge in bm.edges:
    if edge.verts[0].select and edge.verts[1].select:
        edge.select = True

bm.to_mesh(me)
bm.free()

enter image description here

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    $\begingroup$ As always - very nice zeffi :) $\endgroup$ Commented Mar 26, 2015 at 11:32
  • $\begingroup$ @poor thanks! I always answer these questions with at least a working solution, in the hope that someone who knows more will get agitated and offer an alternative. The more answers the merrier. $\endgroup$ Commented Mar 26, 2015 at 11:47
  • $\begingroup$ I've only thought about if there is a build-in epsilon value, remembered vaguely there was one in c++, but can't find it at the moment. $\endgroup$ Commented Mar 26, 2015 at 11:58
  • $\begingroup$ How come import bmesh as bm bm.edges will output bmesh has no attribute edges $\endgroup$ Commented Dec 11, 2020 at 18:33
  • $\begingroup$ @JuneWang because if you import bmesh as bm , then bm is just an alias for the bmesh module, and you are doing something like bm = bm.new()? look at the examples at docs.blender.org/api/blender2.8/… $\endgroup$ Commented Dec 12, 2020 at 12:05

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