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stbi/Lib/site-packages/pip/_vendor/resolvelib/providers.py

+class AbstractProvider(object):
+    """Delegate class to provide requirement interface for the resolver.
+    """
+
+    def identify(self, dependency):
+        """Given a dependency, return an identifier for it.
+
+        This is used in many places to identify the dependency, e.g. whether
+        two requirements should have their specifier parts merged, whether
+        two specifications would conflict with each other (because they the
+        same name but different versions).
+        """
+        raise NotImplementedError
+
+    def get_preference(self, resolution, candidates, information):
+        """Produce a sort key for given specification based on preference.
+
+        The preference is defined as "I think this requirement should be
+        resolved first". The lower the return value is, the more preferred
+        this group of arguments is.
+
+        :param resolution: Currently pinned candidate, or `None`.
+        :param candidates: A list of possible candidates.
+        :param information: A list of requirement information.
+
+        Each information instance is a named tuple with two entries:
+
+        * `requirement` specifies a requirement contributing to the current
+          candidate list
+        * `parent` specifies the candidate that provids (dependend on) the
+          requirement, or `None` to indicate a root requirement.
+
+        The preference could depend on a various of issues, including (not
+        necessarily in this order):
+
+        * Is this package pinned in the current resolution result?
+        * How relaxed is the requirement? Stricter ones should probably be
+          worked on first? (I don't know, actually.)
+        * How many possibilities are there to satisfy this requirement? Those
+          with few left should likely be worked on first, I guess?
+        * Are there any known conflicts for this requirement? We should
+          probably work on those with the most known conflicts.
+
+        A sortable value should be returned (this will be used as the `key`
+        parameter of the built-in sorting function). The smaller the value is,
+        the more preferred this specification is (i.e. the sorting function
+        is called with `reverse=False`).
+        """
+        raise NotImplementedError
+
+    def find_matches(self, requirement):
+        """Find all possible candidates that satisfy a requirement.
+
+        This should try to get candidates based on the requirement's type.
+        For VCS, local, and archive requirements, the one-and-only match is
+        returned, and for a "named" requirement, the index(es) should be
+        consulted to find concrete candidates for this requirement.
+
+        The returned candidates should be sorted by reversed preference, e.g.
+        the most preferred should be LAST. This is done so list-popping can be
+        as efficient as possible.
+        """
+        raise NotImplementedError
+
+    def is_satisfied_by(self, requirement, candidate):
+        """Whether the given requirement can be satisfied by a candidate.
+
+        A boolean should be returned to indicate whether `candidate` is a
+        viable solution to the requirement.
+        """
+        raise NotImplementedError
+
+    def get_dependencies(self, candidate):
+        """Get dependencies of a candidate.
+
+        This should return a collection of requirements that `candidate`
+        specifies as its dependencies.
+        """
+        raise NotImplementedError
+
+
+class AbstractResolver(object):
+    """The thing that performs the actual resolution work.
+    """
+
+    base_exception = Exception
+
+    def __init__(self, provider, reporter):
+        self.provider = provider
+        self.reporter = reporter
+
+    def resolve(self, requirements, **kwargs):
+        """Take a collection of constraints, spit out the resolution result.
+
+        Parameters
+        ----------
+        requirements : Collection
+            A collection of constraints
+        kwargs : optional
+            Additional keyword arguments that subclasses may accept.
+
+        Raises
+        ------
+        self.base_exception
+            Any raised exception is guaranteed to be a subclass of
+            self.base_exception. The string representation of an exception
+            should be human readable and provide context for why it occurred.
+
+        Returns
+        -------
+        retval : object
+            A representation of the final resolution state. It can be any object
+            with a `mapping` attribute that is a Mapping. Other attributes can
+            be used to provide resolver-specific information.
+
+            The `mapping` attribute MUST be key-value pair is an identifier of a
+            requirement (as returned by the provider's `identify` method) mapped
+            to the resolved candidate (chosen from the return value of the
+            provider's `find_matches` method).
+        """
+        raise NotImplementedError