Trac #31640: 2d Bezier path does not plot in 3d

From https://ask.sagemath.org/question/56590/problem-with-plotting-a-3d-
bezier-curve/
{{{
sage: p2d = [[(3.0,0.0),(3.0,0.13),(2.94,0.25),(2.8,0.35)],
[(2.7,0.44),(2.6,0.5),(2.5,0.5)], [(2.36,0.5),(2.24,0.44),(2.14,0.35)],
[(2.05,0.25),(2.0,0.13),(2.0,6.1e-17)]]
sage: bp=bezier_path(p2d)
sage: bp.plot3d()
Traceback (most recent call last):
/opt/sage/local/lib/python3.9/site-packages/sage/symbolic/expression.pyx
in sage.symbolic.expression.Expression._integer_
(build/cythonized/sage/symbolic/expression.cpp:8801)()
   1298         try:
-> 1299             n = self.pyobject()
   1300         except TypeError:

/opt/sage/local/lib/python3.9/site-packages/sage/symbolic/expression.pyx
in sage.symbolic.expression.Expression.pyobject
(build/cythonized/sage/symbolic/expression.cpp:6136)()
    586         if not is_a_numeric(self._gobj):
--> 587             raise TypeError("self must be a numeric expression")
    588         return py_object_from_numeric(self._gobj)

TypeError: self must be a numeric expression

During handling of the above exception, another exception occurred:

TypeError                                 Traceback (most recent call
last)
<ipython-input-6-37e325e9051f> in <module>
----> 1 bp.plot3d()

/opt/sage/local/lib/python3.9/site-packages/sage/plot/graphics.py in
plot3d(self, z, **kwds)
   1279         """
   1280         from sage.plot.plot3d.base import Graphics3dGroup
-> 1281         g = Graphics3dGroup([g.plot3d(**kwds) for g in
self._objects])
   1282         if z:
   1283             g = g.translate(0,0,z)

/opt/sage/local/lib/python3.9/site-packages/sage/plot/graphics.py in
<listcomp>(.0)
   1279         """
   1280         from sage.plot.plot3d.base import Graphics3dGroup
-> 1281         g = Graphics3dGroup([g.plot3d(**kwds) for g in
self._objects])
   1282         if z:
   1283             g = g.translate(0,0,z)

/opt/sage/local/lib/python3.9/site-packages/sage/plot/bezier_path.py in
plot3d(self, z, **kwds)
    168         options = self._plot3d_options()
    169         options.update(kwds)
--> 170         return bezier3d([[(x,y,0) for x,y in self.path[i]] for i
in range(len(self.path))], **options)
    171
    172     def _repr_(self):

/opt/sage/local/lib/python3.9/site-packages/sage/misc/decorators.py in
wrapper(*args, **kwds)
    649                     kwds[new_name] = kwds[old_name]
    650                     del kwds[old_name]
--> 651             return func(*args, **kwds)
    652
    653         return wrapper

/opt/sage/local/lib/python3.9/site-packages/sage/misc/decorators.py in
wrapper(*args, **kwds)
    489                 options['__original_opts'] = kwds
    490             options.update(kwds)
--> 491             return func(*args, **options)
    492
    493         #Add the options specified by @options to the signature
of the wrapped

/opt/sage/local/lib/python3.9/site-packages/sage/plot/plot3d/shapes2.py
in bezier3d(path, **options)
    244             p2 = vector(curve[-2])
    245             p3 = vector(curve[-1])
--> 246             B =
(1-t)**3*p0+3*t*(1-t)**2*p1+3*t**2*(1-t)*p2+t**3*p3
    247             G += P3D.parametric_plot3d(list(B), (0, 1),
color=options['color'], aspect_ratio=options['aspect_ratio'],
thickness=options['thickness'], opacity=options['opacity'])
    248         else:

/opt/sage/local/lib/python3.9/site-packages/sage/symbolic/expression.pyx
in sage.symbolic.expression.Expression.__index__
(build/cythonized/sage/symbolic/expression.cpp:34734)()
   5985             [0, 1, 2, 3, 4]
   5986         """
-> 5987         return int(self._integer_())
   5988
   5989     def iterator(self):

/opt/sage/local/lib/python3.9/site-packages/sage/symbolic/expression.pyx
in sage.symbolic.expression.Expression._integer_
(build/cythonized/sage/symbolic/expression.cpp:8850)()
   1299             n = self.pyobject()
   1300         except TypeError:
-> 1301             raise TypeError("unable to convert %r to an integer"
% self)
   1302         if isinstance(n, sage.rings.integer.Integer):
   1303             return n

TypeError: unable to convert -(t - 1)^3 to an integer
}}}

URL: https://trac.sagemath.org/31640
Reported by: vdelecroix
Ticket author(s): Vincent Delecroix
Reviewer(s): Frédéric Chapoton

Author: Release Manager

build/pkgs/configure/checksums.ini

@@ -1,4 +1,4 @@
 tarball=configure-VERSION.tar.gz
-sha1=2cf3baba7d337a43d19e7b98ec2175d09b2b2a1d
-md5=8933ea22d6d4d30dbde6caeeace4fa64
-cksum=3069515967
+sha1=d37a1359ffb0a2a12c9fc2291799c7a70c2ab36d
+md5=59e93d77644d585380ce40498374ad77
+cksum=4017757244

build/pkgs/configure/package-version.txt

@@ -1 +1 @@
-24a792f72807d9525d9c79a60cf135d034343e3c
+0ccc48bc712b5080b3117a13f33871c3dba45a29

src/sage/plot/plot3d/shapes2.py

@@ -225,6 +225,19 @@ def bezier3d(path, **options):
         sage: curve = bezier3d(path, thickness=5, color='blue')
         sage: curve
         Graphics3d Object
+
+    TESTS:
+
+    Check for :trac:`31640`::
+
+        sage: p2d = [[(3,0.0),(3,0.13),(2,0.2),(2,0.3)], [(2.7,0.4),(2.6,0.5),(2.5,0.5)], [(2.3,0.5),(2.2,0.4),(2.1,0.3)]]
+        sage: bp = bezier_path(p2d)
+        sage: bp.plot3d()
+        Graphics3d Object
+
+        sage: p3d = p3d = [[(3,0,0),(3,0.1,0),(2.9,0.2,0),(2.8,0.3,0)], [(2.7,0.4,0),(2,0.5,0),(2.5,0.5,0)], [(2.3,0.5,0),(2.2,0.4,0),(2.1,0.3,0)]]
+        sage: bezier3d(p3d)
+        Graphics3d Object
     """
     from . import parametric_plot3d as P3D
     from sage.modules.free_module_element import vector
@@ -247,7 +260,7 @@ def bezier3d(path, **options):
             G += P3D.parametric_plot3d(list(B), (0, 1), color=options['color'], aspect_ratio=options['aspect_ratio'], thickness=options['thickness'], opacity=options['opacity'])
         else:
             G += line3d([p0,curve[0]], color=options['color'], thickness=options['thickness'], opacity=options['opacity'])
-        p0 = curve[-1]
+        p0 = vector(curve[-1])
     return G
 
 @rename_keyword(alpha='opacity')