Testing for features of the environment at runtime

A computation can require a certain package to be installed in the runtime environment. Abstractly such a package describes a Feature which can be tested for at runtime. It can be of various kinds, most prominently an Executable in the PATH, a PythonModule, or an additional package for some installed system such as a GapPackage.

AUTHORS:

  • Julian Rüth (2016-04-07): Initial version

  • Jeroen Demeyer (2018-02-12): Refactoring and clean up

EXAMPLES:

Some generic features are available for common cases. For example, to test for the existence of a binary, one can use an Executable feature:

sage: from sage.features import Executable
sage: Executable(name='sh', executable='sh').is_present()
FeatureTestResult('sh', True)

>>> from sage.all import *
>>> from sage.features import Executable
>>> Executable(name='sh', executable='sh').is_present()
FeatureTestResult('sh', True)

Here we test whether the grape GAP package is available:

sage: from sage.features.gap import GapPackage
sage: GapPackage("grape", spkg='gap_packages').is_present()  # optional - gap_package_grape
FeatureTestResult('gap_package_grape', True)

>>> from sage.all import *
>>> from sage.features.gap import GapPackage
>>> GapPackage("grape", spkg='gap_packages').is_present()  # optional - gap_package_grape
FeatureTestResult('gap_package_grape', True)

Note that a FeatureTestResult acts like a bool in most contexts:

sage: if Executable(name='sh', executable='sh').is_present(): "present."
'present.'

>>> from sage.all import *
>>> if Executable(name='sh', executable='sh').is_present(): "present."
'present.'

When one wants to raise an error if the feature is not available, one can use the require method:

sage: Executable(name='sh', executable='sh').require()

sage: Executable(name='random', executable='randomOochoz6x', spkg='random', url='http://rand.om').require() # optional - sage_spkg
Traceback (most recent call last):
...
FeatureNotPresentError: random is not available.
Executable 'randomOochoz6x' not found on PATH.
...try to run...sage -i random...
Further installation instructions might be available at http://rand.om.

>>> from sage.all import *
>>> Executable(name='sh', executable='sh').require()

>>> Executable(name='random', executable='randomOochoz6x', spkg='random', url='http://rand.om').require() # optional - sage_spkg
Traceback (most recent call last):
...
FeatureNotPresentError: random is not available.
Executable 'randomOochoz6x' not found on PATH.
...try to run...sage -i random...
Further installation instructions might be available at http://rand.om.

As can be seen above, features try to produce helpful error messages.

class sage.features.CythonFeature(*args, **kwds)[source]

Bases: Feature

A Feature which describes the ability to compile and import a particular piece of Cython code.

To test the presence of name, the cython compiler is run on test_code and the resulting module is imported.

EXAMPLES:

sage: from sage.features import CythonFeature
sage: fabs_test_code = '''
....: cdef extern from "<math.h>":
....:     double fabs(double x)
....:
....: assert fabs(-1) == 1
....: '''
sage: fabs = CythonFeature("fabs", test_code=fabs_test_code,                    # needs sage.misc.cython
....:                      spkg='gcc', url='https://gnu.org',
....:                      type='standard')
sage: fabs.is_present()                                                         # needs sage.misc.cython
FeatureTestResult('fabs', True)

>>> from sage.all import *
>>> from sage.features import CythonFeature
>>> fabs_test_code = '''
... cdef extern from "<math.h>":
...     double fabs(double x)
....:
>>> assert fabs(-Integer(1)) == Integer(1)
... '''
>>> fabs = CythonFeature("fabs", test_code=fabs_test_code,                    # needs sage.misc.cython
...                      spkg='gcc', url='https://gnu.org',
...                      type='standard')
>>> fabs.is_present()                                                         # needs sage.misc.cython
FeatureTestResult('fabs', True)

Test various failures:

sage: broken_code = '''this is not a valid Cython program!'''
sage: broken = CythonFeature("broken", test_code=broken_code)
sage: broken.is_present()
FeatureTestResult('broken', False)

>>> from sage.all import *
>>> broken_code = '''this is not a valid Cython program!'''
>>> broken = CythonFeature("broken", test_code=broken_code)
>>> broken.is_present()
FeatureTestResult('broken', False)


sage: broken_code = '''cdef extern from "no_such_header_file": pass'''
sage: broken = CythonFeature("broken", test_code=broken_code)
sage: broken.is_present()
FeatureTestResult('broken', False)

>>> from sage.all import *
>>> broken_code = '''cdef extern from "no_such_header_file": pass'''
>>> broken = CythonFeature("broken", test_code=broken_code)
>>> broken.is_present()
FeatureTestResult('broken', False)


sage: broken_code = '''import no_such_python_module'''
sage: broken = CythonFeature("broken", test_code=broken_code)
sage: broken.is_present()
FeatureTestResult('broken', False)

>>> from sage.all import *
>>> broken_code = '''import no_such_python_module'''
>>> broken = CythonFeature("broken", test_code=broken_code)
>>> broken.is_present()
FeatureTestResult('broken', False)


sage: broken_code = '''raise AssertionError("sorry!")'''
sage: broken = CythonFeature("broken", test_code=broken_code)
sage: broken.is_present()
FeatureTestResult('broken', False)

>>> from sage.all import *
>>> broken_code = '''raise AssertionError("sorry!")'''
>>> broken = CythonFeature("broken", test_code=broken_code)
>>> broken.is_present()
FeatureTestResult('broken', False)
class sage.features.Executable(*args, **kwds)[source]

Bases: FileFeature

A feature describing an executable in the PATH.

In an installation of Sage with SAGE_LOCAL different from SAGE_VENV, the executable is searched first in SAGE_VENV/bin, then in SAGE_LOCAL/bin, then in PATH.

Note

Overwrite is_functional() if you also want to check whether the executable shows proper behaviour.

Calls to is_present() are cached. You might want to cache the Executable object to prevent unnecessary calls to the executable.

EXAMPLES:

sage: from sage.features import Executable
sage: Executable(name='sh', executable='sh').is_present()
FeatureTestResult('sh', True)
sage: Executable(name='does-not-exist', executable='does-not-exist-xxxxyxyyxyy').is_present()
FeatureTestResult('does-not-exist', False)

>>> from sage.all import *
>>> from sage.features import Executable
>>> Executable(name='sh', executable='sh').is_present()
FeatureTestResult('sh', True)
>>> Executable(name='does-not-exist', executable='does-not-exist-xxxxyxyyxyy').is_present()
FeatureTestResult('does-not-exist', False)
absolute_filename()[source]

The absolute path of the executable as a string.

EXAMPLES:

sage: from sage.features import Executable
sage: Executable(name='sh', executable='sh').absolute_filename()
'/...bin/sh'

>>> from sage.all import *
>>> from sage.features import Executable
>>> Executable(name='sh', executable='sh').absolute_filename()
'/...bin/sh'

A FeatureNotPresentError is raised if the file cannot be found:

sage: Executable(name='does-not-exist', executable='does-not-exist-xxxxyxyyxyy').absolute_filename()
Traceback (most recent call last):
...
sage.features.FeatureNotPresentError: does-not-exist is not available.
Executable 'does-not-exist-xxxxyxyyxyy' not found on PATH.

>>> from sage.all import *
>>> Executable(name='does-not-exist', executable='does-not-exist-xxxxyxyyxyy').absolute_filename()
Traceback (most recent call last):
...
sage.features.FeatureNotPresentError: does-not-exist is not available.
Executable 'does-not-exist-xxxxyxyyxyy' not found on PATH.
is_functional()[source]

Return whether an executable in the path is functional.

This method is used internally and can be overridden in subclasses in order to implement a feature test. It should not be called directly. Use Feature.is_present() instead.

EXAMPLES:

The function returns True unless explicitly overwritten:

sage: from sage.features import Executable
sage: Executable(name='sh', executable='sh').is_functional()
FeatureTestResult('sh', True)

>>> from sage.all import *
>>> from sage.features import Executable
>>> Executable(name='sh', executable='sh').is_functional()
FeatureTestResult('sh', True)
class sage.features.Feature(*args, **kwds)[source]

Bases: TrivialUniqueRepresentation

A feature of the runtime environment.

INPUT:

  • name – string; name of the feature. This should be suitable as an optional tag for the Sage doctester, i.e., lowercase alphanumeric with underscores (_) allowed; features that correspond to Python modules/packages may use periods (.)

  • spkg – string; name of the SPKG providing the feature

  • description – string (optional); plain English description of the feature

  • url – a URL for the upstream package providing the feature

  • type – string; one of 'standard', 'optional' (default), 'experimental'

Overwrite _is_present() to add feature checks.

EXAMPLES:

sage: from sage.features.gap import GapPackage
sage: GapPackage("grape", spkg='gap_packages')  # indirect doctest
Feature('gap_package_grape')

>>> from sage.all import *
>>> from sage.features.gap import GapPackage
>>> GapPackage("grape", spkg='gap_packages')  # indirect doctest
Feature('gap_package_grape')

For efficiency, features are unique:

sage: GapPackage("grape") is GapPackage("grape")
True

>>> from sage.all import *
>>> GapPackage("grape") is GapPackage("grape")
True
hide()[source]

Hide this feature. For example this is used when the doctest option --hide is set. Setting an installed feature as hidden pretends that it is not available. To revert this use unhide().

EXAMPLES:

Benzene is an optional SPKG. The following test fails if it is hidden or not installed. Thus, in the second invocation the optional tag is needed:

sage: from sage.features.graph_generators import Benzene
sage: Benzene().hide()
sage: len(list(graphs.fusenes(2)))                                          # needs sage.graphs
Traceback (most recent call last):
...
FeatureNotPresentError: benzene is not available.
Feature `benzene` is hidden.
Use method `unhide` to make it available again.

sage: Benzene().unhide()            # optional - benzene, needs sage.graphs
sage: len(list(graphs.fusenes(2)))  # optional - benzene, needs sage.graphs
1

>>> from sage.all import *
>>> from sage.features.graph_generators import Benzene
>>> Benzene().hide()
>>> len(list(graphs.fusenes(Integer(2))))                                          # needs sage.graphs
Traceback (most recent call last):
...
FeatureNotPresentError: benzene is not available.
Feature `benzene` is hidden.
Use method `unhide` to make it available again.

>>> Benzene().unhide()            # optional - benzene, needs sage.graphs
>>> len(list(graphs.fusenes(Integer(2))))  # optional - benzene, needs sage.graphs
1
is_hidden()[source]

Return whether self is present but currently hidden.

EXAMPLES:

sage: from sage.features.sagemath import sage__plot sage: sage__plot().hide() sage: sage__plot().is_hidden() # needs sage.plot True sage: sage__plot().unhide() sage: sage__plot().is_hidden() False

is_optional()[source]

Return whether this feature corresponds to an optional SPKG.

EXAMPLES:

sage: from sage.features.databases import DatabaseCremona
sage: DatabaseCremona().is_optional()
True

>>> from sage.all import *
>>> from sage.features.databases import DatabaseCremona
>>> DatabaseCremona().is_optional()
True
is_present()[source]

Return whether the feature is present.

OUTPUT:

A FeatureTestResult which can be used as a boolean and contains additional information about the feature test.

EXAMPLES:

sage: from sage.features.gap import GapPackage
sage: GapPackage("grape", spkg='gap_packages').is_present()  # optional - gap_package_grape
FeatureTestResult('gap_package_grape', True)
sage: GapPackage("NOT_A_PACKAGE", spkg='gap_packages').is_present()
FeatureTestResult('gap_package_NOT_A_PACKAGE', False)

>>> from sage.all import *
>>> from sage.features.gap import GapPackage
>>> GapPackage("grape", spkg='gap_packages').is_present()  # optional - gap_package_grape
FeatureTestResult('gap_package_grape', True)
>>> GapPackage("NOT_A_PACKAGE", spkg='gap_packages').is_present()
FeatureTestResult('gap_package_NOT_A_PACKAGE', False)

The result is cached:

sage: from sage.features import Feature
sage: class TestFeature(Feature):
....:     def _is_present(self):
....:         print("checking presence")
....:         return True
sage: TestFeature("test").is_present()
checking presence
FeatureTestResult('test', True)
sage: TestFeature("test").is_present()
FeatureTestResult('test', True)
sage: TestFeature("other").is_present()
checking presence
FeatureTestResult('other', True)
sage: TestFeature("other").is_present()
FeatureTestResult('other', True)

>>> from sage.all import *
>>> from sage.features import Feature
>>> class TestFeature(Feature):
...     def _is_present(self):
...         print("checking presence")
...         return True
>>> TestFeature("test").is_present()
checking presence
FeatureTestResult('test', True)
>>> TestFeature("test").is_present()
FeatureTestResult('test', True)
>>> TestFeature("other").is_present()
checking presence
FeatureTestResult('other', True)
>>> TestFeature("other").is_present()
FeatureTestResult('other', True)
is_standard()[source]

Return whether this feature corresponds to a standard SPKG.

EXAMPLES:

sage: from sage.features.databases import DatabaseCremona
sage: DatabaseCremona().is_standard()
False

>>> from sage.all import *
>>> from sage.features.databases import DatabaseCremona
>>> DatabaseCremona().is_standard()
False
joined_features()[source]

Return a list of features that self is the join of.

OUTPUT:

A (possibly empty) list of instances of Feature.

EXAMPLES:

sage: from sage.features.graphviz import Graphviz
sage: Graphviz().joined_features()
[Feature('dot'), Feature('neato'), Feature('twopi')]
sage: from sage.features.sagemath import sage__rings__function_field
sage: sage__rings__function_field().joined_features()
[Feature('sage.rings.function_field.function_field_polymod'),
Feature('sage.libs.singular'),
Feature('sage.libs.singular.singular'),
Feature('sage.interfaces.singular')]
sage: from sage.features.interfaces import Mathematica
sage: Mathematica().joined_features()
[]

>>> from sage.all import *
>>> from sage.features.graphviz import Graphviz
>>> Graphviz().joined_features()
[Feature('dot'), Feature('neato'), Feature('twopi')]
>>> from sage.features.sagemath import sage__rings__function_field
>>> sage__rings__function_field().joined_features()
[Feature('sage.rings.function_field.function_field_polymod'),
Feature('sage.libs.singular'),
Feature('sage.libs.singular.singular'),
Feature('sage.interfaces.singular')]
>>> from sage.features.interfaces import Mathematica
>>> Mathematica().joined_features()
[]
require()[source]

Raise a FeatureNotPresentError if the feature is not present.

EXAMPLES:

sage: from sage.features.gap import GapPackage
sage: GapPackage("ve1EeThu").require()                                      # needs sage.libs.gap
Traceback (most recent call last):
...
FeatureNotPresentError: gap_package_ve1EeThu is not available.
`LoadPackage("ve1EeThu")` evaluated to `fail` in GAP.

>>> from sage.all import *
>>> from sage.features.gap import GapPackage
>>> GapPackage("ve1EeThu").require()                                      # needs sage.libs.gap
Traceback (most recent call last):
...
FeatureNotPresentError: gap_package_ve1EeThu is not available.
`LoadPackage("ve1EeThu")` evaluated to `fail` in GAP.
resolution()[source]

Return a suggestion on how to make is_present() pass if it did not pass.

OUTPUT: string

EXAMPLES:

sage: from sage.features import Executable
sage: Executable(name='CSDP', spkg='csdp', executable='theta', url='https://github.com/dimpase/csdp').resolution()  # optional - sage_spkg
'...To install CSDP...you can try to run...sage -i csdp...Further installation instructions might be available at https://github.com/dimpase/csdp.'

>>> from sage.all import *
>>> from sage.features import Executable
>>> Executable(name='CSDP', spkg='csdp', executable='theta', url='https://github.com/dimpase/csdp').resolution()  # optional - sage_spkg
'...To install CSDP...you can try to run...sage -i csdp...Further installation instructions might be available at https://github.com/dimpase/csdp.'
unhide()[source]

Revert what hide() did.

EXAMPLES:

sage: from sage.features.sagemath import sage__plot sage: sage__plot().hide() sage: sage__plot().is_present() FeatureTestResult(‘sage.plot’, False) sage: sage__plot().unhide() # needs sage.plot sage: sage__plot().is_present() # needs sage.plot FeatureTestResult(‘sage.plot’, True)

exception sage.features.FeatureNotPresentError(feature, reason=None, resolution=None)[source]

Bases: RuntimeError

A missing feature error.

EXAMPLES:

sage: from sage.features import Feature, FeatureTestResult
sage: class Missing(Feature):
....:     def _is_present(self):
....:         return False

sage: Missing(name='missing').require()
Traceback (most recent call last):
...
FeatureNotPresentError: missing is not available.

>>> from sage.all import *
>>> from sage.features import Feature, FeatureTestResult
>>> class Missing(Feature):
...     def _is_present(self):
...         return False

>>> Missing(name='missing').require()
Traceback (most recent call last):
...
FeatureNotPresentError: missing is not available.
property resolution

Initialize self. See help(type(self)) for accurate signature.

class sage.features.FeatureTestResult(feature, is_present, reason=None, resolution=None)[source]

Bases: object

The result of a Feature.is_present() call.

Behaves like a boolean with some extra data which may explain why a feature is not present and how this may be resolved.

EXAMPLES:

sage: from sage.features.gap import GapPackage
sage: presence = GapPackage("NOT_A_PACKAGE").is_present(); presence  # indirect doctest
FeatureTestResult('gap_package_NOT_A_PACKAGE', False)
sage: bool(presence)
False

>>> from sage.all import *
>>> from sage.features.gap import GapPackage
>>> presence = GapPackage("NOT_A_PACKAGE").is_present(); presence  # indirect doctest
FeatureTestResult('gap_package_NOT_A_PACKAGE', False)
>>> bool(presence)
False

Explanatory messages might be available as reason and resolution:

sage: presence.reason                                                           # needs sage.libs.gap
'`LoadPackage("NOT_A_PACKAGE")` evaluated to `fail` in GAP.'
sage: bool(presence.resolution)
False

>>> from sage.all import *
>>> presence.reason                                                           # needs sage.libs.gap
'`LoadPackage("NOT_A_PACKAGE")` evaluated to `fail` in GAP.'
>>> bool(presence.resolution)
False

If a feature is not present, resolution defaults to feature.resolution() if this is defined. If you do not want to use this default you need explicitly set resolution to a string:

sage: from sage.features import FeatureTestResult
sage: package = GapPackage("NOT_A_PACKAGE", spkg='no_package')
sage: str(FeatureTestResult(package, True).resolution)  # optional - sage_spkg
'...To install gap_package_NOT_A_PACKAGE...you can try to run...sage -i no_package...'
sage: str(FeatureTestResult(package, False).resolution) # optional - sage_spkg
'...To install gap_package_NOT_A_PACKAGE...you can try to run...sage -i no_package...'
sage: FeatureTestResult(package, False, resolution='rtm').resolution
'rtm'

>>> from sage.all import *
>>> from sage.features import FeatureTestResult
>>> package = GapPackage("NOT_A_PACKAGE", spkg='no_package')
>>> str(FeatureTestResult(package, True).resolution)  # optional - sage_spkg
'...To install gap_package_NOT_A_PACKAGE...you can try to run...sage -i no_package...'
>>> str(FeatureTestResult(package, False).resolution) # optional - sage_spkg
'...To install gap_package_NOT_A_PACKAGE...you can try to run...sage -i no_package...'
>>> FeatureTestResult(package, False, resolution='rtm').resolution
'rtm'
property resolution

Initialize self. See help(type(self)) for accurate signature.

class sage.features.FileFeature(*args, **kwds)[source]

Bases: Feature

Base class for features that describe a file or directory in the file system.

A subclass should implement a method absolute_filename().

EXAMPLES:

Two direct concrete subclasses of FileFeature are defined:

sage: from sage.features import StaticFile, Executable, FileFeature
sage: issubclass(StaticFile, FileFeature)
True
sage: issubclass(Executable, FileFeature)
True

>>> from sage.all import *
>>> from sage.features import StaticFile, Executable, FileFeature
>>> issubclass(StaticFile, FileFeature)
True
>>> issubclass(Executable, FileFeature)
True

To work with the file described by the feature, use the method absolute_filename(). A FeatureNotPresentError is raised if the file cannot be found:

sage: Executable(name='does-not-exist', executable='does-not-exist-xxxxyxyyxyy').absolute_filename()
Traceback (most recent call last):
...
sage.features.FeatureNotPresentError: does-not-exist is not available.
Executable 'does-not-exist-xxxxyxyyxyy' not found on PATH.

>>> from sage.all import *
>>> Executable(name='does-not-exist', executable='does-not-exist-xxxxyxyyxyy').absolute_filename()
Traceback (most recent call last):
...
sage.features.FeatureNotPresentError: does-not-exist is not available.
Executable 'does-not-exist-xxxxyxyyxyy' not found on PATH.

A FileFeature also provides the is_present() method to test for the presence of the file at run time. This is inherited from the base class Feature:

sage: Executable(name='sh', executable='sh').is_present()
FeatureTestResult('sh', True)

>>> from sage.all import *
>>> Executable(name='sh', executable='sh').is_present()
FeatureTestResult('sh', True)
absolute_filename()[source]

The absolute path of the file as a string.

Concrete subclasses must override this abstract method.

class sage.features.PythonModule(*args, **kwds)[source]

Bases: Feature

A Feature which describes whether a python module can be imported.

EXAMPLES:

Not all builds of python include the ssl module, so you could check whether it is available:

sage: from sage.features import PythonModule
sage: PythonModule("ssl").require()  # not tested - output depends on the python build

>>> from sage.all import *
>>> from sage.features import PythonModule
>>> PythonModule("ssl").require()  # not tested - output depends on the python build
class sage.features.StaticFile(*args, **kwds)[source]

Bases: FileFeature

A Feature which describes the presence of a certain file such as a database.

EXAMPLES:

sage: from sage.features import StaticFile
sage: StaticFile(name='no_such_file', filename='KaT1aihu',              # optional - sage_spkg
....:            search_path='/', spkg='some_spkg',
....:            url='http://rand.om').require()
Traceback (most recent call last):
...
FeatureNotPresentError: no_such_file is not available.
'KaT1aihu' not found in any of ['/']...
To install no_such_file...you can try to run...sage -i some_spkg...
Further installation instructions might be available at http://rand.om.

>>> from sage.all import *
>>> from sage.features import StaticFile
>>> StaticFile(name='no_such_file', filename='KaT1aihu',              # optional - sage_spkg
...            search_path='/', spkg='some_spkg',
...            url='http://rand.om').require()
Traceback (most recent call last):
...
FeatureNotPresentError: no_such_file is not available.
'KaT1aihu' not found in any of ['/']...
To install no_such_file...you can try to run...sage -i some_spkg...
Further installation instructions might be available at http://rand.om.
absolute_filename()[source]

The absolute path of the file as a string.

EXAMPLES:

sage: from sage.features import StaticFile
sage: from sage.misc.temporary_file import tmp_dir
sage: dir_with_file = tmp_dir()
sage: file_path = os.path.join(dir_with_file, "file.txt")
sage: open(file_path, 'a').close() # make sure the file exists
sage: search_path = ( '/foo/bar', dir_with_file ) # file is somewhere in the search path
sage: feature = StaticFile(name='file', filename='file.txt', search_path=search_path)
sage: feature.absolute_filename() == file_path
True

>>> from sage.all import *
>>> from sage.features import StaticFile
>>> from sage.misc.temporary_file import tmp_dir
>>> dir_with_file = tmp_dir()
>>> file_path = os.path.join(dir_with_file, "file.txt")
>>> open(file_path, 'a').close() # make sure the file exists
>>> search_path = ( '/foo/bar', dir_with_file ) # file is somewhere in the search path
>>> feature = StaticFile(name='file', filename='file.txt', search_path=search_path)
>>> feature.absolute_filename() == file_path
True

A FeatureNotPresentError is raised if the file cannot be found:

sage: from sage.features import StaticFile
sage: StaticFile(name='no_such_file', filename='KaT1aihu',\
                 search_path=(), spkg='some_spkg',\
                 url='http://rand.om').absolute_filename()  # optional - sage_spkg
Traceback (most recent call last):
...
FeatureNotPresentError: no_such_file is not available.
'KaT1aihu' not found in any of []...
To install no_such_file...you can try to run...sage -i some_spkg...
Further installation instructions might be available at http://rand.om.

>>> from sage.all import *
>>> from sage.features import StaticFile
>>> StaticFile(name='no_such_file', filename='KaT1aihu',\
                 search_path=(), spkg='some_spkg',\
                 url='http://rand.om').absolute_filename()  # optional - sage_spkg
Traceback (most recent call last):
...
FeatureNotPresentError: no_such_file is not available.
'KaT1aihu' not found in any of []...
To install no_such_file...you can try to run...sage -i some_spkg...
Further installation instructions might be available at http://rand.om.
class sage.features.TrivialClasscallMetaClass[source]

Bases: type

A trivial version of sage.misc.classcall_metaclass.ClasscallMetaclass without Cython dependencies.

class sage.features.TrivialUniqueRepresentation(*args, **kwds)[source]

Bases: object

A trivial version of UniqueRepresentation without Cython dependencies.

sage.features.package_systems()[source]

Return a list of PackageSystem objects representing the available package systems.

The list is ordered by decreasing preference.

EXAMPLES:

sage: from sage.features import package_systems
sage: package_systems()    # random
[Feature('homebrew'), Feature('sage_spkg'), Feature('pip')]

>>> from sage.all import *
>>> from sage.features import package_systems
>>> package_systems()    # random
[Feature('homebrew'), Feature('sage_spkg'), Feature('pip')]