Add Features to check the environment at runtime

Eventually this should replace is_package_installed()
checks which are annoying for packagers.

src/sage/game_theory/normal_form_game.py

@@ -618,7 +618,6 @@
 from sage.structure.sage_object import SageObject
 from sage.matrix.constructor import matrix
 from sage.matrix.constructor import vector
-from sage.misc.package import is_package_installed, PackageNotFoundError
 from sage.misc.temporary_file import tmp_filename
 from sage.numerical.mip import MixedIntegerLinearProgram
 
@@ -1633,18 +1632,17 @@ def obtain_nash(self, algorithm=False, maximization=True, solver=None):
         if not self._is_complete():
             raise ValueError("utilities have not been populated")
 
+        from sage.misc.feature_test import Lrs
         if not algorithm:
             if self.is_constant_sum():
                 algorithm = "lp"
-            elif is_package_installed('lrslib'):
+            elif Lrs().is_present():
                 algorithm = "lrs"
             else:
                 algorithm = "enumeration"
 
         if algorithm == "lrs":
-            if not is_package_installed('lrslib'):
-                raise PackageNotFoundError("lrslib")
-
+            Lrs().require()
             return self._solve_lrs(maximization)
 
         if algorithm == "LCP":

src/sage/geometry/polyhedron/base.py

@@ -22,7 +22,6 @@
 from sage.structure.richcmp import rich_to_bool, op_NE
 
 from sage.misc.all import cached_method, prod
-from sage.misc.package import is_package_installed, PackageNotFoundError
 from sage.misc.randstate import current_randstate
 
 from sage.rings.all import QQ, ZZ, AA
@@ -4281,8 +4280,7 @@ def _volume_lrs(self, verbose=False):
 
              David Avis's lrs program.
         """
-        if not is_package_installed('lrslib'):
-            raise PackageNotFoundError('lrslib')
+        Lrs().require()
 
         from sage.misc.temporary_file import tmp_filename
         from subprocess import Popen, PIPE

src/sage/graphs/bliss.pyx

@@ -49,7 +49,6 @@ cdef extern from "bliss/graph.hh" namespace "bliss":
                     const unsigned int*), void*)
 
     cdef cppclass Digraph(AbstractGraph):
-
         Digraph(const unsigned int)
         void add_edge(const unsigned int, const unsigned int)
         void find_automorphisms(Stats&, void (*)(void* , unsigned int,

src/sage/graphs/generators/classical_geometries.py

@@ -1284,12 +1284,10 @@ def CossidentePenttilaGraph(q):
     if k==0 or p==2:
         raise ValueError('q(={}) must be an odd prime power'.format(q))
 
-    from sage.libs.gap.libgap import libgap
-    from sage.misc.package import is_package_installed, PackageNotFoundError
-
-    if not is_package_installed('gap_packages'):
-        raise PackageNotFoundError('gap_packages')
+    from sage.misc.feature_test import GapPackage
+    GapPackage("grape", spkg="gap_packages").require()
 
+    from sage.libs.gap.libgap import libgap
     adj_list=libgap.function_factory("""function(q)
         local z, e, so, G, nu, G1, G0, B, T, s, O1, O2, x;
         LoadPackage("grape");

src/sage/graphs/generic_graph.py

@@ -8462,7 +8462,6 @@ def flow(self, x, y, value_only=True, integer=False, use_edge_labels=True, verte
            sage: abs(flow_ff-flow_igraph) < 0.00001         # optional python_igraph
            True
         """
-        from sage.misc.package import is_package_installed, PackageNotFoundError
         self._scream_if_not_simple(allow_loops=True)
         if vertex_bound and algorithm in ["FF", "igraph"]:
             raise ValueError("This method does not support both " +
@@ -8478,9 +8477,10 @@ def flow(self, x, y, value_only=True, integer=False, use_edge_labels=True, verte
             capacity=lambda x: 1
 
         if algorithm is None:
+            from sage.misc.feature_test import Module
             if vertex_bound:
                 algorithm = "LP"
-            elif is_package_installed("python_igraph"):
+            elif Module(module="igraph", spkg="python_igraph", url="http://igraph.org").is_present():
                 algorithm = "igraph"
             else:
                 algorithm = "FF"
@@ -21845,11 +21845,8 @@ def automorphism_group(self, partition=None, verbosity=0,
             [Subgroup of (Permutation Group with generators [(0,7)(1,4)(2,3)(6,8)]) generated by [()],
             Subgroup of (Permutation Group with generators [(0,7)(1,4)(2,3)(6,8)]) generated by [(0,7)(1,4)(2,3)(6,8)]]
         """
-        try:
-            from sage.graphs.bliss import automorphism_group
-            have_bliss = True
-        except ImportError:
-            have_bliss = False
+        from sage.features.bliss import Bliss
+        have_bliss = Bliss().is_present()
 
         # See trac #21704
         if self.has_multiple_edges():
@@ -21864,10 +21861,9 @@ def automorphism_group(self, partition=None, verbosity=0,
             if edge_labels:
                 raise ValueError("bliss cannot be used when edge_labels is True")
 
-            if not have_bliss:
-                from sage.misc.package import PackageNotFoundError
-                raise PackageNotFoundError("bliss")
+            Bliss().require()
 
+            from sage.graphs.bliss import automorphism_group
             A = automorphism_group(self, partition)
 
             # If the user only wants the automorphism group, lets return it

src/sage/graphs/graph_generators.py

@@ -1210,23 +1210,22 @@ def fullerenes(self, order, ipr=False):
         .. [buckygen] \G. Brinkmann, J. Goedgebeur and B.D. McKay, Generation of Fullerenes,
           Journal of Chemical Information and Modeling, 52(11):2910-2918, 2012.
         """
-        from sage.misc.package import is_package_installed, PackageNotFoundError
-        if not is_package_installed("buckygen"):
-            raise PackageNotFoundError("buckygen")
-
         # number of vertices should be positive
         if order < 0:
-            raise ValueError("Number of vertices should be positive.")
+            raise ValueError("number of vertices should be non-negative")
 
         # buckygen can only output fullerenes on up to 254 vertices
         if order > 254:
-            raise ValueError("Number of vertices should be at most 254.")
+            raise ValueError("number of vertices should be at most 254")
 
         # fullerenes only exist for an even number of vertices, larger than 20
         # and different from 22
         if order % 2 == 1 or order < 20 or order == 22:
             return
 
+        from sage.misc.feature_test import Buckygen
+        Buckygen().require()
+
         command = 'buckygen -'+('I' if ipr else '')+'d {0}d'.format(order)
 
         import subprocess
@@ -1295,17 +1294,12 @@ def fusenes(self, hexagon_count, benzenoids=False):
         .. [benzene] \G. Brinkmann, G. Caporossi and P. Hansen, A Constructive Enumeration of Fusenes and Benzenoids,
           Journal of Algorithms, 45:155-166, 2002.
         """
-        from sage.misc.package import is_package_installed, PackageNotFoundError
-        if not is_package_installed("benzene"):
-            raise PackageNotFoundError("benzene")
-
-        # number of hexagons should be positive
         if hexagon_count < 0:
-            raise ValueError("Number of hexagons should be positive.")
+            raise ValueError("number of hexagons should be non-negative")
 
         # benzene is only built for fusenes with up to 30 hexagons
         if hexagon_count > 30:
-            raise ValueError("Number of hexagons should be at most 30.")
+            raise ValueError("number of hexagons should be at most 30")
 
         # there are no fusenes with 0 hexagons
         if hexagon_count == 0:
@@ -1319,6 +1313,9 @@ def fusenes(self, hexagon_count, benzenoids=False):
             yield(G)
             return
 
+        from sage.misc.feature_test import Benzene
+        Benzene().require()
+
         command = 'benzene '+('b' if benzenoids else '')+' {0} p'.format(hexagon_count)
 
         import subprocess
@@ -1448,22 +1445,16 @@ def planar_graphs(self, order, minimum_degree=None,
         .. [plantri] \G. Brinkmann and B.D. McKay, Fast generation of planar graphs,
            MATCH-Communications in Mathematical and in Computer Chemistry, 58(2):323-357, 2007.
         """
-        from sage.misc.package import is_package_installed, PackageNotFoundError
-        if not is_package_installed("plantri"):
-            raise PackageNotFoundError("plantri")
-
-        # number of vertices should be positive
         if order < 0:
-            raise ValueError("Number of vertices should be positive.")
+            raise ValueError("number of vertices should be non-negative")
 
         # plantri can only output general planar graphs on up to 64 vertices
         if order > 64:
-            raise ValueError("Number of vertices should be at most 64.")
+            raise ValueError("number of vertices should be at most 64")
 
         if exact_connectivity and minimum_connectivity is None:
             raise ValueError("Minimum connectivity must be specified to use the exact_connectivity option.")
 
-        # minimum connectivity should be None or a number between 1 and 3
         if minimum_connectivity is  not None and not (1 <= minimum_connectivity <= 3):
             raise ValueError("Minimum connectivity should be a number between 1 and 3.")
 
@@ -1511,6 +1502,9 @@ def planar_graphs(self, order, minimum_degree=None,
                 yield(G)
             return
 
+        from sage.misc.feature_test import Plantri
+        Plantri().require()
+
         cmd = 'plantri -p{}m{}c{}{}{} {}'
         command = cmd.format('b' if only_bipartite else '',
                              minimum_degree,
@@ -1647,26 +1641,19 @@ def triangulations(self, order, minimum_degree=None, minimum_connectivity=None,
             sage: [g.size() for g in graphs.triangulations(6, minimum_connectivity=3)] # optional plantri
             [12, 12]
         """
-        from sage.misc.package import is_package_installed, PackageNotFoundError
-        if not is_package_installed("plantri"):
-            raise PackageNotFoundError("plantri")
-
-        # number of vertices should be positive
         if order < 0:
-            raise ValueError("Number of vertices should be positive.")
+            raise ValueError("number of vertices should be non-negative")
 
         # plantri can only output planar triangulations on up to 64 vertices
         if order > 64:
-            raise ValueError("Number of vertices should be at most 64.")
+            raise ValueError("number of vertices should be at most 64")
 
         if exact_connectivity and minimum_connectivity is None:
             raise ValueError("Minimum connectivity must be specified to use the exact_connectivity option.")
 
-        # minimum connectivity should be None or a number between 3 and 5
         if minimum_connectivity is  not None and not (3 <= minimum_connectivity <= 5):
             raise ValueError("Minimum connectivity should be None or a number between 3 and 5.")
 
-        # minimum degree should be None or a number between 3 and 5
         if minimum_degree is  not None and not (3 <= minimum_degree <= 5):
             raise ValueError("Minimum degree should be None or a number between 3 and 5.")
 
@@ -1698,6 +1685,9 @@ def triangulations(self, order, minimum_degree=None, minimum_connectivity=None,
         if only_eulerian and order < 6:
             return
 
+        from sage.misc.feature_test import Plantri
+        Plantri().require()
+
         cmd = 'plantri -{}m{}c{}{}{} {}'
         command = cmd.format('b' if only_eulerian else '',
                              minimum_degree,
@@ -1801,23 +1791,16 @@ def quadrangulations(self, order, minimum_degree=None, minimum_connectivity=None
             sage: [len(g) for g in graphs.quadrangulations(12, no_nonfacial_quadrangles=True, dual=True)]  # optional plantri
             [10, 10]
         """
-        from sage.misc.package import is_package_installed, PackageNotFoundError
-        if not is_package_installed("plantri"):
-            raise PackageNotFoundError("plantri")
-
-        # number of vertices should be positive
         if order < 0:
-            raise ValueError("Number of vertices should be positive.")
+            raise ValueError("number of vertices should be non-negative")
 
         # plantri can only output planar quadrangulations on up to 64 vertices
         if order > 64:
-            raise ValueError("Number of vertices should be at most 64.")
+            raise ValueError("number of vertices should be at most 64")
 
-        # minimum connectivity should be None, 2 or 3
         if minimum_connectivity not in {None, 2, 3}:
             raise ValueError("Minimum connectivity should be None, 2 or 3.")
 
-        # minimum degree should be None, 2 or 3
         if minimum_degree not in {None, 2, 3}:
             raise ValueError("Minimum degree should be None, 2 or 3.")
 
@@ -1846,6 +1829,8 @@ def quadrangulations(self, order, minimum_degree=None, minimum_connectivity=None
             # for plantri -q the option -c4 means 3-connected with no non-facial quadrangles
             minimum_connectivity = 4
 
+        from sage.misc.feature_test import Plantri
+        Plantri().require()
 
         cmd = 'plantri -qm{}c{}{} {}'
         command = cmd.format(minimum_degree,
@@ -2516,6 +2501,5 @@ def check_aut_edge(aut_gens, cut_edge, i, j, n, dig=False):
                 if not dig and new_perm[cut_edge[0]] == j and new_perm[cut_edge[1]] == i:
                     yield new_perm
 
-
 # Easy access to the graph generators from the command line:
 graphs = GraphGenerators()

src/sage/graphs/lovasz_theta.py

@@ -64,17 +64,15 @@ def lovasz_theta(graph):
     from networkx import write_edgelist
     from sage.misc.temporary_file import tmp_filename
     import os, subprocess
-    from sage.env import SAGE_LOCAL
-    from sage.misc.package import is_package_installed, PackageNotFoundError
 
-    if not is_package_installed('csdp'):
-        raise PackageNotFoundError("csdp")
+    from sage.misc.feature import CSDP
+    CSDP().require()
 
     g = graph.relabel(inplace=False, perm=range(1,n+1)).networkx_graph()
     tf_name = tmp_filename()
     tf = open(tf_name, 'wb')
     tf.write(str(n)+'\n'+str(g.number_of_edges())+'\n')
     write_edgelist(g, tf, data=False)
     tf.close()
-    lines = subprocess.check_output([os.path.join(SAGE_LOCAL, 'bin', 'theta'), tf_name])
+    lines = subprocess.check_output(['theta', tf_name])
     return float(lines.split()[-1])

src/sage/groups/generic.py

@@ -1406,15 +1406,15 @@ def structure_description(G, latex=False):
         'A8'
     """
     import re
-    from sage.misc.package import is_package_installed, PackageNotFoundError
     def correct_dihedral_degree(match):
         return "%sD%d" % (match.group(1), int(match.group(2))/2)
 
     try:
         description = str(G._gap_().StructureDescription())
     except RuntimeError:
-        if not is_package_installed('database_gap'):
-            raise PackageNotFoundError("database_gap")
+        from sage.misc.feature_test import SmallGroupsLibrary
+        SmallGroupsLibrary().require()
+        # the Small Groups Library is installed. The command failed for a different reason
         raise
 
     description = re.sub(r"(\A|\W)D(\d+)", correct_dihedral_degree, description)