--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/env/lib/python3.7/site-packages/packaging/specifiers.py	Sat May 02 07:14:21 2020 -0400
@@ -0,0 +1,849 @@
+# This file is dual licensed under the terms of the Apache License, Version
+# 2.0, and the BSD License. See the LICENSE file in the root of this repository
+# for complete details.
+from __future__ import absolute_import, division, print_function
+
+import abc
+import functools
+import itertools
+import re
+
+from ._compat import string_types, with_metaclass
+from ._typing import MYPY_CHECK_RUNNING
+from .version import Version, LegacyVersion, parse
+
+if MYPY_CHECK_RUNNING:  # pragma: no cover
+    from typing import (
+        List,
+        Dict,
+        Union,
+        Iterable,
+        Iterator,
+        Optional,
+        Callable,
+        Tuple,
+        FrozenSet,
+    )
+
+    ParsedVersion = Union[Version, LegacyVersion]
+    UnparsedVersion = Union[Version, LegacyVersion, str]
+    CallableOperator = Callable[[ParsedVersion, str], bool]
+
+
+class InvalidSpecifier(ValueError):
+    """
+    An invalid specifier was found, users should refer to PEP 440.
+    """
+
+
+class BaseSpecifier(with_metaclass(abc.ABCMeta, object)):  # type: ignore
+    @abc.abstractmethod
+    def __str__(self):
+        # type: () -> str
+        """
+        Returns the str representation of this Specifier like object. This
+        should be representative of the Specifier itself.
+        """
+
+    @abc.abstractmethod
+    def __hash__(self):
+        # type: () -> int
+        """
+        Returns a hash value for this Specifier like object.
+        """
+
+    @abc.abstractmethod
+    def __eq__(self, other):
+        # type: (object) -> bool
+        """
+        Returns a boolean representing whether or not the two Specifier like
+        objects are equal.
+        """
+
+    @abc.abstractmethod
+    def __ne__(self, other):
+        # type: (object) -> bool
+        """
+        Returns a boolean representing whether or not the two Specifier like
+        objects are not equal.
+        """
+
+    @abc.abstractproperty
+    def prereleases(self):
+        # type: () -> Optional[bool]
+        """
+        Returns whether or not pre-releases as a whole are allowed by this
+        specifier.
+        """
+
+    @prereleases.setter
+    def prereleases(self, value):
+        # type: (bool) -> None
+        """
+        Sets whether or not pre-releases as a whole are allowed by this
+        specifier.
+        """
+
+    @abc.abstractmethod
+    def contains(self, item, prereleases=None):
+        # type: (str, Optional[bool]) -> bool
+        """
+        Determines if the given item is contained within this specifier.
+        """
+
+    @abc.abstractmethod
+    def filter(self, iterable, prereleases=None):
+        # type: (Iterable[UnparsedVersion], Optional[bool]) -> Iterable[UnparsedVersion]
+        """
+        Takes an iterable of items and filters them so that only items which
+        are contained within this specifier are allowed in it.
+        """
+
+
+class _IndividualSpecifier(BaseSpecifier):
+
+    _operators = {}  # type: Dict[str, str]
+
+    def __init__(self, spec="", prereleases=None):
+        # type: (str, Optional[bool]) -> None
+        match = self._regex.search(spec)
+        if not match:
+            raise InvalidSpecifier("Invalid specifier: '{0}'".format(spec))
+
+        self._spec = (
+            match.group("operator").strip(),
+            match.group("version").strip(),
+        )  # type: Tuple[str, str]
+
+        # Store whether or not this Specifier should accept prereleases
+        self._prereleases = prereleases
+
+    def __repr__(self):
+        # type: () -> str
+        pre = (
+            ", prereleases={0!r}".format(self.prereleases)
+            if self._prereleases is not None
+            else ""
+        )
+
+        return "<{0}({1!r}{2})>".format(self.__class__.__name__, str(self), pre)
+
+    def __str__(self):
+        # type: () -> str
+        return "{0}{1}".format(*self._spec)
+
+    def __hash__(self):
+        # type: () -> int
+        return hash(self._spec)
+
+    def __eq__(self, other):
+        # type: (object) -> bool
+        if isinstance(other, string_types):
+            try:
+                other = self.__class__(str(other))
+            except InvalidSpecifier:
+                return NotImplemented
+        elif not isinstance(other, self.__class__):
+            return NotImplemented
+
+        return self._spec == other._spec
+
+    def __ne__(self, other):
+        # type: (object) -> bool
+        if isinstance(other, string_types):
+            try:
+                other = self.__class__(str(other))
+            except InvalidSpecifier:
+                return NotImplemented
+        elif not isinstance(other, self.__class__):
+            return NotImplemented
+
+        return self._spec != other._spec
+
+    def _get_operator(self, op):
+        # type: (str) -> CallableOperator
+        operator_callable = getattr(
+            self, "_compare_{0}".format(self._operators[op])
+        )  # type: CallableOperator
+        return operator_callable
+
+    def _coerce_version(self, version):
+        # type: (UnparsedVersion) -> ParsedVersion
+        if not isinstance(version, (LegacyVersion, Version)):
+            version = parse(version)
+        return version
+
+    @property
+    def operator(self):
+        # type: () -> str
+        return self._spec[0]
+
+    @property
+    def version(self):
+        # type: () -> str
+        return self._spec[1]
+
+    @property
+    def prereleases(self):
+        # type: () -> Optional[bool]
+        return self._prereleases
+
+    @prereleases.setter
+    def prereleases(self, value):
+        # type: (bool) -> None
+        self._prereleases = value
+
+    def __contains__(self, item):
+        # type: (str) -> bool
+        return self.contains(item)
+
+    def contains(self, item, prereleases=None):
+        # type: (UnparsedVersion, Optional[bool]) -> bool
+
+        # Determine if prereleases are to be allowed or not.
+        if prereleases is None:
+            prereleases = self.prereleases
+
+        # Normalize item to a Version or LegacyVersion, this allows us to have
+        # a shortcut for ``"2.0" in Specifier(">=2")
+        normalized_item = self._coerce_version(item)
+
+        # Determine if we should be supporting prereleases in this specifier
+        # or not, if we do not support prereleases than we can short circuit
+        # logic if this version is a prereleases.
+        if normalized_item.is_prerelease and not prereleases:
+            return False
+
+        # Actually do the comparison to determine if this item is contained
+        # within this Specifier or not.
+        operator_callable = self._get_operator(self.operator)  # type: CallableOperator
+        return operator_callable(normalized_item, self.version)
+
+    def filter(self, iterable, prereleases=None):
+        # type: (Iterable[UnparsedVersion], Optional[bool]) -> Iterable[UnparsedVersion]
+
+        yielded = False
+        found_prereleases = []
+
+        kw = {"prereleases": prereleases if prereleases is not None else True}
+
+        # Attempt to iterate over all the values in the iterable and if any of
+        # them match, yield them.
+        for version in iterable:
+            parsed_version = self._coerce_version(version)
+
+            if self.contains(parsed_version, **kw):
+                # If our version is a prerelease, and we were not set to allow
+                # prereleases, then we'll store it for later incase nothing
+                # else matches this specifier.
+                if parsed_version.is_prerelease and not (
+                    prereleases or self.prereleases
+                ):
+                    found_prereleases.append(version)
+                # Either this is not a prerelease, or we should have been
+                # accepting prereleases from the beginning.
+                else:
+                    yielded = True
+                    yield version
+
+        # Now that we've iterated over everything, determine if we've yielded
+        # any values, and if we have not and we have any prereleases stored up
+        # then we will go ahead and yield the prereleases.
+        if not yielded and found_prereleases:
+            for version in found_prereleases:
+                yield version
+
+
+class LegacySpecifier(_IndividualSpecifier):
+
+    _regex_str = r"""
+        (?P<operator>(==|!=|<=|>=|<|>))
+        \s*
+        (?P<version>
+            [^,;\s)]* # Since this is a "legacy" specifier, and the version
+                      # string can be just about anything, we match everything
+                      # except for whitespace, a semi-colon for marker support,
+                      # a closing paren since versions can be enclosed in
+                      # them, and a comma since it's a version separator.
+        )
+        """
+
+    _regex = re.compile(r"^\s*" + _regex_str + r"\s*$", re.VERBOSE | re.IGNORECASE)
+
+    _operators = {
+        "==": "equal",
+        "!=": "not_equal",
+        "<=": "less_than_equal",
+        ">=": "greater_than_equal",
+        "<": "less_than",
+        ">": "greater_than",
+    }
+
+    def _coerce_version(self, version):
+        # type: (Union[ParsedVersion, str]) -> LegacyVersion
+        if not isinstance(version, LegacyVersion):
+            version = LegacyVersion(str(version))
+        return version
+
+    def _compare_equal(self, prospective, spec):
+        # type: (LegacyVersion, str) -> bool
+        return prospective == self._coerce_version(spec)
+
+    def _compare_not_equal(self, prospective, spec):
+        # type: (LegacyVersion, str) -> bool
+        return prospective != self._coerce_version(spec)
+
+    def _compare_less_than_equal(self, prospective, spec):
+        # type: (LegacyVersion, str) -> bool
+        return prospective <= self._coerce_version(spec)
+
+    def _compare_greater_than_equal(self, prospective, spec):
+        # type: (LegacyVersion, str) -> bool
+        return prospective >= self._coerce_version(spec)
+
+    def _compare_less_than(self, prospective, spec):
+        # type: (LegacyVersion, str) -> bool
+        return prospective < self._coerce_version(spec)
+
+    def _compare_greater_than(self, prospective, spec):
+        # type: (LegacyVersion, str) -> bool
+        return prospective > self._coerce_version(spec)
+
+
+def _require_version_compare(
+    fn  # type: (Callable[[Specifier, ParsedVersion, str], bool])
+):
+    # type: (...) -> Callable[[Specifier, ParsedVersion, str], bool]
+    @functools.wraps(fn)
+    def wrapped(self, prospective, spec):
+        # type: (Specifier, ParsedVersion, str) -> bool
+        if not isinstance(prospective, Version):
+            return False
+        return fn(self, prospective, spec)
+
+    return wrapped
+
+
+class Specifier(_IndividualSpecifier):
+
+    _regex_str = r"""
+        (?P<operator>(~=|==|!=|<=|>=|<|>|===))
+        (?P<version>
+            (?:
+                # The identity operators allow for an escape hatch that will
+                # do an exact string match of the version you wish to install.
+                # This will not be parsed by PEP 440 and we cannot determine
+                # any semantic meaning from it. This operator is discouraged
+                # but included entirely as an escape hatch.
+                (?<====)  # Only match for the identity operator
+                \s*
+                [^\s]*    # We just match everything, except for whitespace
+                          # since we are only testing for strict identity.
+            )
+            |
+            (?:
+                # The (non)equality operators allow for wild card and local
+                # versions to be specified so we have to define these two
+                # operators separately to enable that.
+                (?<===|!=)            # Only match for equals and not equals
+
+                \s*
+                v?
+                (?:[0-9]+!)?          # epoch
+                [0-9]+(?:\.[0-9]+)*   # release
+                (?:                   # pre release
+                    [-_\.]?
+                    (a|b|c|rc|alpha|beta|pre|preview)
+                    [-_\.]?
+                    [0-9]*
+                )?
+                (?:                   # post release
+                    (?:-[0-9]+)|(?:[-_\.]?(post|rev|r)[-_\.]?[0-9]*)
+                )?
+
+                # You cannot use a wild card and a dev or local version
+                # together so group them with a | and make them optional.
+                (?:
+                    (?:[-_\.]?dev[-_\.]?[0-9]*)?         # dev release
+                    (?:\+[a-z0-9]+(?:[-_\.][a-z0-9]+)*)? # local
+                    |
+                    \.\*  # Wild card syntax of .*
+                )?
+            )
+            |
+            (?:
+                # The compatible operator requires at least two digits in the
+                # release segment.
+                (?<=~=)               # Only match for the compatible operator
+
+                \s*
+                v?
+                (?:[0-9]+!)?          # epoch
+                [0-9]+(?:\.[0-9]+)+   # release  (We have a + instead of a *)
+                (?:                   # pre release
+                    [-_\.]?
+                    (a|b|c|rc|alpha|beta|pre|preview)
+                    [-_\.]?
+                    [0-9]*
+                )?
+                (?:                                   # post release
+                    (?:-[0-9]+)|(?:[-_\.]?(post|rev|r)[-_\.]?[0-9]*)
+                )?
+                (?:[-_\.]?dev[-_\.]?[0-9]*)?          # dev release
+            )
+            |
+            (?:
+                # All other operators only allow a sub set of what the
+                # (non)equality operators do. Specifically they do not allow
+                # local versions to be specified nor do they allow the prefix
+                # matching wild cards.
+                (?<!==|!=|~=)         # We have special cases for these
+                                      # operators so we want to make sure they
+                                      # don't match here.
+
+                \s*
+                v?
+                (?:[0-9]+!)?          # epoch
+                [0-9]+(?:\.[0-9]+)*   # release
+                (?:                   # pre release
+                    [-_\.]?
+                    (a|b|c|rc|alpha|beta|pre|preview)
+                    [-_\.]?
+                    [0-9]*
+                )?
+                (?:                                   # post release
+                    (?:-[0-9]+)|(?:[-_\.]?(post|rev|r)[-_\.]?[0-9]*)
+                )?
+                (?:[-_\.]?dev[-_\.]?[0-9]*)?          # dev release
+            )
+        )
+        """
+
+    _regex = re.compile(r"^\s*" + _regex_str + r"\s*$", re.VERBOSE | re.IGNORECASE)
+
+    _operators = {
+        "~=": "compatible",
+        "==": "equal",
+        "!=": "not_equal",
+        "<=": "less_than_equal",
+        ">=": "greater_than_equal",
+        "<": "less_than",
+        ">": "greater_than",
+        "===": "arbitrary",
+    }
+
+    @_require_version_compare
+    def _compare_compatible(self, prospective, spec):
+        # type: (ParsedVersion, str) -> bool
+
+        # Compatible releases have an equivalent combination of >= and ==. That
+        # is that ~=2.2 is equivalent to >=2.2,==2.*. This allows us to
+        # implement this in terms of the other specifiers instead of
+        # implementing it ourselves. The only thing we need to do is construct
+        # the other specifiers.
+
+        # We want everything but the last item in the version, but we want to
+        # ignore post and dev releases and we want to treat the pre-release as
+        # it's own separate segment.
+        prefix = ".".join(
+            list(
+                itertools.takewhile(
+                    lambda x: (not x.startswith("post") and not x.startswith("dev")),
+                    _version_split(spec),
+                )
+            )[:-1]
+        )
+
+        # Add the prefix notation to the end of our string
+        prefix += ".*"
+
+        return self._get_operator(">=")(prospective, spec) and self._get_operator("==")(
+            prospective, prefix
+        )
+
+    @_require_version_compare
+    def _compare_equal(self, prospective, spec):
+        # type: (ParsedVersion, str) -> bool
+
+        # We need special logic to handle prefix matching
+        if spec.endswith(".*"):
+            # In the case of prefix matching we want to ignore local segment.
+            prospective = Version(prospective.public)
+            # Split the spec out by dots, and pretend that there is an implicit
+            # dot in between a release segment and a pre-release segment.
+            split_spec = _version_split(spec[:-2])  # Remove the trailing .*
+
+            # Split the prospective version out by dots, and pretend that there
+            # is an implicit dot in between a release segment and a pre-release
+            # segment.
+            split_prospective = _version_split(str(prospective))
+
+            # Shorten the prospective version to be the same length as the spec
+            # so that we can determine if the specifier is a prefix of the
+            # prospective version or not.
+            shortened_prospective = split_prospective[: len(split_spec)]
+
+            # Pad out our two sides with zeros so that they both equal the same
+            # length.
+            padded_spec, padded_prospective = _pad_version(
+                split_spec, shortened_prospective
+            )
+
+            return padded_prospective == padded_spec
+        else:
+            # Convert our spec string into a Version
+            spec_version = Version(spec)
+
+            # If the specifier does not have a local segment, then we want to
+            # act as if the prospective version also does not have a local
+            # segment.
+            if not spec_version.local:
+                prospective = Version(prospective.public)
+
+            return prospective == spec_version
+
+    @_require_version_compare
+    def _compare_not_equal(self, prospective, spec):
+        # type: (ParsedVersion, str) -> bool
+        return not self._compare_equal(prospective, spec)
+
+    @_require_version_compare
+    def _compare_less_than_equal(self, prospective, spec):
+        # type: (ParsedVersion, str) -> bool
+        return prospective <= Version(spec)
+
+    @_require_version_compare
+    def _compare_greater_than_equal(self, prospective, spec):
+        # type: (ParsedVersion, str) -> bool
+        return prospective >= Version(spec)
+
+    @_require_version_compare
+    def _compare_less_than(self, prospective, spec_str):
+        # type: (ParsedVersion, str) -> bool
+
+        # Convert our spec to a Version instance, since we'll want to work with
+        # it as a version.
+        spec = Version(spec_str)
+
+        # Check to see if the prospective version is less than the spec
+        # version. If it's not we can short circuit and just return False now
+        # instead of doing extra unneeded work.
+        if not prospective < spec:
+            return False
+
+        # This special case is here so that, unless the specifier itself
+        # includes is a pre-release version, that we do not accept pre-release
+        # versions for the version mentioned in the specifier (e.g. <3.1 should
+        # not match 3.1.dev0, but should match 3.0.dev0).
+        if not spec.is_prerelease and prospective.is_prerelease:
+            if Version(prospective.base_version) == Version(spec.base_version):
+                return False
+
+        # If we've gotten to here, it means that prospective version is both
+        # less than the spec version *and* it's not a pre-release of the same
+        # version in the spec.
+        return True
+
+    @_require_version_compare
+    def _compare_greater_than(self, prospective, spec_str):
+        # type: (ParsedVersion, str) -> bool
+
+        # Convert our spec to a Version instance, since we'll want to work with
+        # it as a version.
+        spec = Version(spec_str)
+
+        # Check to see if the prospective version is greater than the spec
+        # version. If it's not we can short circuit and just return False now
+        # instead of doing extra unneeded work.
+        if not prospective > spec:
+            return False
+
+        # This special case is here so that, unless the specifier itself
+        # includes is a post-release version, that we do not accept
+        # post-release versions for the version mentioned in the specifier
+        # (e.g. >3.1 should not match 3.0.post0, but should match 3.2.post0).
+        if not spec.is_postrelease and prospective.is_postrelease:
+            if Version(prospective.base_version) == Version(spec.base_version):
+                return False
+
+        # Ensure that we do not allow a local version of the version mentioned
+        # in the specifier, which is technically greater than, to match.
+        if prospective.local is not None:
+            if Version(prospective.base_version) == Version(spec.base_version):
+                return False
+
+        # If we've gotten to here, it means that prospective version is both
+        # greater than the spec version *and* it's not a pre-release of the
+        # same version in the spec.
+        return True
+
+    def _compare_arbitrary(self, prospective, spec):
+        # type: (Version, str) -> bool
+        return str(prospective).lower() == str(spec).lower()
+
+    @property
+    def prereleases(self):
+        # type: () -> bool
+
+        # If there is an explicit prereleases set for this, then we'll just
+        # blindly use that.
+        if self._prereleases is not None:
+            return self._prereleases
+
+        # Look at all of our specifiers and determine if they are inclusive
+        # operators, and if they are if they are including an explicit
+        # prerelease.
+        operator, version = self._spec
+        if operator in ["==", ">=", "<=", "~=", "==="]:
+            # The == specifier can include a trailing .*, if it does we
+            # want to remove before parsing.
+            if operator == "==" and version.endswith(".*"):
+                version = version[:-2]
+
+            # Parse the version, and if it is a pre-release than this
+            # specifier allows pre-releases.
+            if parse(version).is_prerelease:
+                return True
+
+        return False
+
+    @prereleases.setter
+    def prereleases(self, value):
+        # type: (bool) -> None
+        self._prereleases = value
+
+
+_prefix_regex = re.compile(r"^([0-9]+)((?:a|b|c|rc)[0-9]+)$")
+
+
+def _version_split(version):
+    # type: (str) -> List[str]
+    result = []  # type: List[str]
+    for item in version.split("."):
+        match = _prefix_regex.search(item)
+        if match:
+            result.extend(match.groups())
+        else:
+            result.append(item)
+    return result
+
+
+def _pad_version(left, right):
+    # type: (List[str], List[str]) -> Tuple[List[str], List[str]]
+    left_split, right_split = [], []
+
+    # Get the release segment of our versions
+    left_split.append(list(itertools.takewhile(lambda x: x.isdigit(), left)))
+    right_split.append(list(itertools.takewhile(lambda x: x.isdigit(), right)))
+
+    # Get the rest of our versions
+    left_split.append(left[len(left_split[0]) :])
+    right_split.append(right[len(right_split[0]) :])
+
+    # Insert our padding
+    left_split.insert(1, ["0"] * max(0, len(right_split[0]) - len(left_split[0])))
+    right_split.insert(1, ["0"] * max(0, len(left_split[0]) - len(right_split[0])))
+
+    return (list(itertools.chain(*left_split)), list(itertools.chain(*right_split)))
+
+
+class SpecifierSet(BaseSpecifier):
+    def __init__(self, specifiers="", prereleases=None):
+        # type: (str, Optional[bool]) -> None
+
+        # Split on , to break each individual specifier into it's own item, and
+        # strip each item to remove leading/trailing whitespace.
+        split_specifiers = [s.strip() for s in specifiers.split(",") if s.strip()]
+
+        # Parsed each individual specifier, attempting first to make it a
+        # Specifier and falling back to a LegacySpecifier.
+        parsed = set()
+        for specifier in split_specifiers:
+            try:
+                parsed.add(Specifier(specifier))
+            except InvalidSpecifier:
+                parsed.add(LegacySpecifier(specifier))
+
+        # Turn our parsed specifiers into a frozen set and save them for later.
+        self._specs = frozenset(parsed)
+
+        # Store our prereleases value so we can use it later to determine if
+        # we accept prereleases or not.
+        self._prereleases = prereleases
+
+    def __repr__(self):
+        # type: () -> str
+        pre = (
+            ", prereleases={0!r}".format(self.prereleases)
+            if self._prereleases is not None
+            else ""
+        )
+
+        return "<SpecifierSet({0!r}{1})>".format(str(self), pre)
+
+    def __str__(self):
+        # type: () -> str
+        return ",".join(sorted(str(s) for s in self._specs))
+
+    def __hash__(self):
+        # type: () -> int
+        return hash(self._specs)
+
+    def __and__(self, other):
+        # type: (Union[SpecifierSet, str]) -> SpecifierSet
+        if isinstance(other, string_types):
+            other = SpecifierSet(other)
+        elif not isinstance(other, SpecifierSet):
+            return NotImplemented
+
+        specifier = SpecifierSet()
+        specifier._specs = frozenset(self._specs | other._specs)
+
+        if self._prereleases is None and other._prereleases is not None:
+            specifier._prereleases = other._prereleases
+        elif self._prereleases is not None and other._prereleases is None:
+            specifier._prereleases = self._prereleases
+        elif self._prereleases == other._prereleases:
+            specifier._prereleases = self._prereleases
+        else:
+            raise ValueError(
+                "Cannot combine SpecifierSets with True and False prerelease "
+                "overrides."
+            )
+
+        return specifier
+
+    def __eq__(self, other):
+        # type: (object) -> bool
+        if isinstance(other, (string_types, _IndividualSpecifier)):
+            other = SpecifierSet(str(other))
+        elif not isinstance(other, SpecifierSet):
+            return NotImplemented
+
+        return self._specs == other._specs
+
+    def __ne__(self, other):
+        # type: (object) -> bool
+        if isinstance(other, (string_types, _IndividualSpecifier)):
+            other = SpecifierSet(str(other))
+        elif not isinstance(other, SpecifierSet):
+            return NotImplemented
+
+        return self._specs != other._specs
+
+    def __len__(self):
+        # type: () -> int
+        return len(self._specs)
+
+    def __iter__(self):
+        # type: () -> Iterator[FrozenSet[_IndividualSpecifier]]
+        return iter(self._specs)
+
+    @property
+    def prereleases(self):
+        # type: () -> Optional[bool]
+
+        # If we have been given an explicit prerelease modifier, then we'll
+        # pass that through here.
+        if self._prereleases is not None:
+            return self._prereleases
+
+        # If we don't have any specifiers, and we don't have a forced value,
+        # then we'll just return None since we don't know if this should have
+        # pre-releases or not.
+        if not self._specs:
+            return None
+
+        # Otherwise we'll see if any of the given specifiers accept
+        # prereleases, if any of them do we'll return True, otherwise False.
+        return any(s.prereleases for s in self._specs)
+
+    @prereleases.setter
+    def prereleases(self, value):
+        # type: (bool) -> None
+        self._prereleases = value
+
+    def __contains__(self, item):
+        # type: (Union[ParsedVersion, str]) -> bool
+        return self.contains(item)
+
+    def contains(self, item, prereleases=None):
+        # type: (Union[ParsedVersion, str], Optional[bool]) -> bool
+
+        # Ensure that our item is a Version or LegacyVersion instance.
+        if not isinstance(item, (LegacyVersion, Version)):
+            item = parse(item)
+
+        # Determine if we're forcing a prerelease or not, if we're not forcing
+        # one for this particular filter call, then we'll use whatever the
+        # SpecifierSet thinks for whether or not we should support prereleases.
+        if prereleases is None:
+            prereleases = self.prereleases
+
+        # We can determine if we're going to allow pre-releases by looking to
+        # see if any of the underlying items supports them. If none of them do
+        # and this item is a pre-release then we do not allow it and we can
+        # short circuit that here.
+        # Note: This means that 1.0.dev1 would not be contained in something
+        #       like >=1.0.devabc however it would be in >=1.0.debabc,>0.0.dev0
+        if not prereleases and item.is_prerelease:
+            return False
+
+        # We simply dispatch to the underlying specs here to make sure that the
+        # given version is contained within all of them.
+        # Note: This use of all() here means that an empty set of specifiers
+        #       will always return True, this is an explicit design decision.
+        return all(s.contains(item, prereleases=prereleases) for s in self._specs)
+
+    def filter(
+        self,
+        iterable,  # type: Iterable[Union[ParsedVersion, str]]
+        prereleases=None,  # type: Optional[bool]
+    ):
+        # type: (...) -> Iterable[Union[ParsedVersion, str]]
+
+        # Determine if we're forcing a prerelease or not, if we're not forcing
+        # one for this particular filter call, then we'll use whatever the
+        # SpecifierSet thinks for whether or not we should support prereleases.
+        if prereleases is None:
+            prereleases = self.prereleases
+
+        # If we have any specifiers, then we want to wrap our iterable in the
+        # filter method for each one, this will act as a logical AND amongst
+        # each specifier.
+        if self._specs:
+            for spec in self._specs:
+                iterable = spec.filter(iterable, prereleases=bool(prereleases))
+            return iterable
+        # If we do not have any specifiers, then we need to have a rough filter
+        # which will filter out any pre-releases, unless there are no final
+        # releases, and which will filter out LegacyVersion in general.
+        else:
+            filtered = []  # type: List[Union[ParsedVersion, str]]
+            found_prereleases = []  # type: List[Union[ParsedVersion, str]]
+
+            for item in iterable:
+                # Ensure that we some kind of Version class for this item.
+                if not isinstance(item, (LegacyVersion, Version)):
+                    parsed_version = parse(item)
+                else:
+                    parsed_version = item
+
+                # Filter out any item which is parsed as a LegacyVersion
+                if isinstance(parsed_version, LegacyVersion):
+                    continue
+
+                # Store any item which is a pre-release for later unless we've
+                # already found a final version or we are accepting prereleases
+                if parsed_version.is_prerelease and not prereleases:
+                    if not filtered:
+                        found_prereleases.append(item)
+                else:
+                    filtered.append(item)
+
+            # If we've found no items except for pre-releases, then we'll go
+            # ahead and use the pre-releases
+            if not filtered and found_prereleases and prereleases is None:
+                return found_prereleases
+
+            return filtered