Trac #28022: Downgrade rubiks to optional

See discussion in
https://groups.google.com/forum/?utm_medium=email&utm_source=footer#!msg
/sage-devel/lc-HqYCFrDw/r4TlV6qCBAAJ

URL: https://trac.sagemath.org/28022
Reported by: isuruf
Ticket author(s): Frédéric Chapoton, John Palmieri
Reviewer(s): Dima Pasechnik, Matthias Koeppe

build/pkgs/rubiks/SPKG.rst

@@ -20,7 +20,7 @@ Dik T. Winter (MIT License)
    solution to the 3x3x3 Rubik's cube
 -  size222 - solves a 2x2x2 Rubik's cube
 
-Eric Dietz (GPL) http://www.wrongway.org/?rubiksource
+Eric Dietz (GPL) https://web.archive.org/web/20121212175710/http://www.wrongway.org/?rubiksource
 
 -  cu2 - A fast, non-optimal 2x2x2 solver
 -  cubex - A fast, non-optimal 3x3x3 solver

build/pkgs/rubiks/type

@@ -1 +1 @@
-standard
+optional

src/sage/doctest/external.py

@@ -289,6 +289,20 @@ def has_imagemagick():
     from sage.features.imagemagick import ImageMagick
     return ImageMagick().is_present()
 
+def has_rubiks():
+    """
+    Test if the rubiks package (``cu2``, ``cubex``, ``dikcube``,
+    ``mcube``, ``optimal``, and ``size222``) is available.
+
+    EXAMPLES::
+
+        sage: from sage.doctest.external import has_rubiks
+        sage: has_rubiks()   # optional -- rubiks
+        FeatureTestResult('Rubiks', True)
+    """
+    from sage.features.rubiks import Rubiks
+    return Rubiks().is_present()
+
 def external_software():
     """
     Return the alphabetical list of external software supported by this module.
@@ -345,6 +359,7 @@ class AvailableSoftware(object):
          'matlab',
          'octave',
          'pandoc',
+         'rubiks',
          'scilab']
         sage: 'internet' in available_software # random, optional - internet
         True

src/sage/features/rubiks.py

@@ -0,0 +1,192 @@
+# -*- coding: utf-8 -*-
+r"""
+Check for rubiks
+"""
+# ****************************************************************************
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 2 of the License, or
+# (at your option) any later version.
+#                  https://www.gnu.org/licenses/
+# ****************************************************************************
+from . import Feature, Executable, FeatureTestResult
+
+class cu2(Executable):
+    r"""
+    A :class:`sage.features.Executable` describing the presence of
+    ``cu2``
+
+    EXAMPLES::
+
+        sage: from sage.features.rubiks import cu2
+        sage: cu2().is_present()  # optional: rubiks
+        FeatureTestResult('cu2', True)
+    """
+    def __init__(self):
+        r"""
+        TESTS::
+
+            sage: from sage.features.rubiks import cu2
+            sage: isinstance(cu2(), cu2)
+            True
+        """
+        Executable.__init__(self, "cu2", executable="cu2",
+                            spkg="rubiks")
+
+
+class size222(Executable):
+    r"""
+    A :class:`sage.features.Executable` describing the presence of
+    ``size222``
+
+    EXAMPLES::
+
+        sage: from sage.features.rubiks import size222
+        sage: size222().is_present()  # optional: rubiks
+        FeatureTestResult('size222', True)
+    """
+    def __init__(self):
+        r"""
+        TESTS::
+
+            sage: from sage.features.rubiks import size222
+            sage: isinstance(size222(), size222)
+            True
+        """
+        Executable.__init__(self, "size222", executable="size222",
+                            spkg="rubiks")
+
+
+class optimal(Executable):
+    r"""
+    A :class:`sage.features.Executable` describing the presence of
+    ``optimal``
+
+    EXAMPLES::
+
+        sage: from sage.features.rubiks import optimal
+        sage: optimal().is_present()  # optional: rubiks
+        FeatureTestResult('optimal', True)
+    """
+    def __init__(self):
+        r"""
+        TESTS::
+
+            sage: from sage.features.rubiks import optimal
+            sage: isinstance(optimal(), optimal)
+            True
+        """
+        Executable.__init__(self, "optimal", executable="optimal",
+                            spkg="rubiks")
+
+
+class mcube(Executable):
+    r"""
+    A :class:`sage.features.Executable` describing the presence of
+    ``mcube``
+
+    EXAMPLES::
+
+        sage: from sage.features.rubiks import mcube
+        sage: mcube().is_present()  # optional: rubiks
+        FeatureTestResult('mcube', True)
+    """
+    def __init__(self):
+        r"""
+        TESTS::
+
+            sage: from sage.features.rubiks import mcube
+            sage: isinstance(mcube(), mcube)
+            True
+        """
+        Executable.__init__(self, "mcube", executable="mcube",
+                            spkg="rubiks")
+
+
+class dikcube(Executable):
+    r"""
+    A :class:`sage.features.Executable` describing the presence of
+    ``dikcube``
+
+    EXAMPLES::
+
+        sage: from sage.features.rubiks import dikcube
+        sage: dikcube().is_present()  # optional: rubiks
+        FeatureTestResult('dikcube', True)
+    """
+    def __init__(self):
+        r"""
+        TESTS::
+
+            sage: from sage.features.rubiks import dikcube
+            sage: isinstance(dikcube(), dikcube)
+            True
+        """
+        Executable.__init__(self, "dikcube", executable="dikcube",
+                            spkg="rubiks")
+
+
+class cubex(Executable):
+    r"""
+    A :class:`sage.features.Executable` describing the presence of
+    ``cubex``
+
+    EXAMPLES::
+
+        sage: from sage.features.rubiks import cubex
+        sage: cubex().is_present()  # optional: rubiks
+        FeatureTestResult('cubex', True)
+    """
+    def __init__(self):
+        r"""
+        TESTS::
+
+            sage: from sage.features.rubiks import cubex
+            sage: isinstance(cubex(), cubex)
+            True
+        """
+        Executable.__init__(self, "cubex", executable="cubex",
+                            spkg="rubiks")
+
+
+class Rubiks(Feature):
+    r"""
+    A :class:`sage.features.Feature` describing the presence of
+    ``cu2``, ``cubex``, ``dikcube``, ``mcube``, ``optimal``, and
+    ``size222``.
+
+    EXAMPLES::
+
+        sage: from sage.features.rubiks import Rubiks
+        sage: Rubiks().is_present()  # optional: rubiks
+        FeatureTestResult('Rubiks', True)
+    """
+    def __init__(self):
+        r"""
+        TESTS::
+
+            sage: from sage.features.rubiks import Rubiks
+            sage: isinstance(Rubiks(), Rubiks)
+            True
+        """
+        Feature.__init__(self, "Rubiks",
+                         spkg="rubiks")
+
+    def _is_present(self):
+        r"""
+        EXAMPLES::
+
+            sage: from sage.features.rubiks import Rubiks
+            sage: Rubiks()._is_present() # optional: rubiks
+            FeatureTestResult('Rubiks', True)
+        """
+        test = (cu2()._is_present() and
+                size222()._is_present() and
+                optimal()._is_present() and
+                mcube()._is_present() and
+                dikcube()._is_present() and
+                cubex()._is_present())
+        if not test:
+            return test
+        else:
+            return FeatureTestResult(self, True)

src/sage/groups/perm_gps/cubegroup.py

@@ -724,7 +724,7 @@ def parse(self, mv, check=True):
                 mv = mv.strip().replace(" ","*").replace("**", "*").replace("'", "-1").replace('^','').replace('(','').replace(')','')
                 M = mv.split("*")
                 for m in M:
-                    if len(m) == 0:
+                    if not m:
                         pass
                     elif len(m) == 1:
                         g *= map[m[0]]
@@ -837,7 +837,7 @@ def move(self, mv):
         g = self.parse(mv)
         return g, self.facets(g)
 
-    def display2d(self,mv):
+    def display2d(self, mv):
         r"""
         Print the 2d representation of ``self``.
 
@@ -950,7 +950,7 @@ def plot_cube(self, mv, title=True, colors = [lpurple, yellow, red, green, orang
             return P
         return clrs
 
-    def plot3d_cube(self,mv,title=True):
+    def plot3d_cube(self, mv, title=True):
         r"""
         Displays `F,U,R` faces of the cube after the given move ``mv``. Mostly
         included for the purpose of drawing pictures and checking moves.
@@ -993,7 +993,7 @@ def plot3d_cube(self,mv,title=True):
             return P
         return P
 
-    def legal(self,state,mode="quiet"):
+    def legal(self, state, mode="quiet"):
         r"""
         Return 1 (true) if the dictionary ``state`` (in the
         same format as returned by the faces method) represents a legal
@@ -1023,9 +1023,9 @@ def legal(self,state,mode="quiet"):
         else:
             return res
 
-    def solve(self,state, algorithm='default'):
+    def solve(self, state, algorithm='default'):
         r"""
-        Solves the cube in the ``state``, given as a dictionary
+        Solve the cube in the ``state``, given as a dictionary
         as in ``legal``. See the ``solve`` method
         of the RubiksCube class for more details.
 
@@ -1082,7 +1082,7 @@ def solve(self,state, algorithm='default'):
             return C.solve(algorithm)
 
         hom = self._gap_().EpimorphismFromFreeGroup()
-        soln = hom.PreImagesRepresentative(gap(str(g)))
+        soln = hom.PreImagesRepresentative(str(g))
         sol = str(soln)
         names = self.gen_names()
         for i in range(6):
@@ -1190,7 +1190,7 @@ class RubiksCube(SageObject):
                      +--------------+
         sage: C.show()
         sage: C.solve(algorithm='gap')  # long time
-        'L R'
+        'L*R'
         sage: C == RubiksCube("L*R")
         True
     """
@@ -1241,7 +1241,7 @@ def undo(self):
             sage: D.undo() == C
             True
         """
-        if len(self._history) == 0:
+        if not self._history:
             raise ValueError("no moves to undo")
         g = self._history[-1]
         return RubiksCube(self._state * ~g, self._history[:-1], self.colors)
@@ -1307,7 +1307,7 @@ def show(self):
         """
         self.plot().show()
 
-    def cubie(self, size, gap, x,y,z, colors, stickers=True):
+    def cubie(self, size, gap, x, y, z, colors, stickers=True):
         """
         Return the cubie at `(x,y,z)`.
 
@@ -1413,22 +1413,30 @@ def solve(self, algorithm="hybrid", timeout=15):
             (may take a long time)
           - ``gap`` - Use GAP word solution (can be slow)
 
+        Any choice other than ``gap`` requires the optional package
+        ``rubiks``. Otherwise, the ``gap`` algorithm is used.
+
         EXAMPLES::
 
             sage: C = RubiksCube("R U F L B D")
-            sage: C.solve()
+            sage: C.solve()           # optional - rubiks
             'R U F L B D'
 
         Dietz's program is much faster, but may give highly non-optimal
         solutions::
 
-            sage: s = C.solve('dietz'); s
+            sage: s = C.solve('dietz'); s   # optional - rubiks
             "U' L' L' U L U' L U D L L D' L' D L' D' L D L' U' L D' L' U L' B' U' L' U B L D L D' U' L' U L B L B' L' U L U' L' F' L' F L' F L F' L' D' L' D D L D' B L B' L B' L B F' L F F B' L F' B D' D' L D B' B' L' D' B U' U' L' B' D' F' F' L D F'"
-            sage: C2 = RubiksCube(s)
-            sage: C == C2
+            sage: C2 = RubiksCube(s)  # optional - rubiks
+            sage: C == C2             # optional - rubiks
             True
         """
-        import sage.interfaces.rubik # here to avoid circular referencing
+        from sage.features.rubiks import Rubiks
+        if Rubiks().is_present():
+            import sage.interfaces.rubik  # here to avoid circular referencing
+        else:
+            algorithm = 'gap'
+
         if algorithm == "default":
             algorithm = "hybrid"
 
@@ -1455,7 +1463,7 @@ def solve(self, algorithm="hybrid", timeout=15):
 
         elif algorithm == "gap":
             solver = CubeGroup()
-            return solver.solve(self._state)
+            return solver.solve(self._state, algorithm="gap")
 
         else:
             raise ValueError("Unrecognized algorithm: %s" % algorithm)
@@ -1491,4 +1499,3 @@ def scramble(self, moves=30):
             last_move = move
             all.append(move)
         return self.move(' '.join(all))
-