text: import io
  import os
  import re
  import abc
  import csv
  import sys
  import email
  import pathlib
  import zipfile
  import operator
  import functools
  import itertools
  import posixpath
  import collections
  
  from configparser import ConfigParser
  from contextlib import suppress
  from importlib import import_module
  from importlib.abc import MetaPathFinder
  from itertools import starmap
  
  
  __all__ = [
      'Distribution',
      'DistributionFinder',
      'PackageNotFoundError',
      'distribution',
      'distributions',
      'entry_points',
      'files',
      'metadata',
      'requires',
      'version',
      ]
  
  
  class PackageNotFoundError(ModuleNotFoundError):
      """The package was not found."""
  
      def __str__(self):
          tmpl = "No package metadata was found for {self.name}"
          return tmpl.format(**locals())
  
      @property
      def name(self):
          name, = self.args
          return name
  
  
  class EntryPoint(
          collections.namedtuple('EntryPointBase', 'name value group')):
      """An entry point as defined by Python packaging conventions.
  
      See `the packaging docs on entry points
      <https://packaging.python.org/specifications/entry-points/>`_
      for more information.
      """
  
      pattern = re.compile(
          r'(?P<module>[\w.]+)\s*'
          r'(:\s*(?P<attr>[\w.]+))?\s*'
          r'(?P<extras>\[.*\])?\s*$'
          )
      """
      A regular expression describing the syntax for an entry point,
      which might look like:
  
          - module
          - package.module
          - package.module:attribute
          - package.module:object.attribute
          - package.module:attr [extra1, extra2]
  
      Other combinations are possible as well.
  
      The expression is lenient about whitespace around the ':',
      following the attr, and following any extras.
      """
  
      def load(self):
          """Load the entry point from its definition. If only a module
          is indicated by the value, return that module. Otherwise,
          return the named object.
          """
          match = self.pattern.match(self.value)
          module = import_module(match.group('module'))
          attrs = filter(None, (match.group('attr') or '').split('.'))
          return functools.reduce(getattr, attrs, module)
  
      @property
      def module(self):
          match = self.pattern.match(self.value)
          return match.group('module')
  
      @property
      def attr(self):
          match = self.pattern.match(self.value)
          return match.group('attr')
  
      @property
      def extras(self):
          match = self.pattern.match(self.value)
          return list(re.finditer(r'\w+', match.group('extras') or ''))
  
      @classmethod
      def _from_config(cls, config):
          return [
              cls(name, value, group)
              for group in config.sections()
              for name, value in config.items(group)
              ]
  
      @classmethod
      def _from_text(cls, text):
          config = ConfigParser(delimiters='=')
          # case sensitive: https://stackoverflow.com/q/1611799/812183
          config.optionxform = str
          try:
              config.read_string(text)
          except AttributeError:  # pragma: nocover
              # Python 2 has no read_string
              config.readfp(io.StringIO(text))
          return EntryPoint._from_config(config)
  
      def __iter__(self):
          """
          Supply iter so one may construct dicts of EntryPoints easily.
          """
          return iter((self.name, self))
  
      def __reduce__(self):
          return (
              self.__class__,
              (self.name, self.value, self.group),
              )
  
  
  class PackagePath(pathlib.PurePosixPath):
      """A reference to a path in a package"""
  
      def read_text(self, encoding='utf-8'):
          with self.locate().open(encoding=encoding) as stream:
              return stream.read()
  
      def read_binary(self):
          with self.locate().open('rb') as stream:
              return stream.read()
  
      def locate(self):
          """Return a path-like object for this path"""
          return self.dist.locate_file(self)
  
  
  class FileHash:
      def __init__(self, spec):
          self.mode, _, self.value = spec.partition('=')
  
      def __repr__(self):
          return '<FileHash mode: {} value: {}>'.format(self.mode, self.value)
  
  
  class Distribution:
      """A Python distribution package."""
  
      @abc.abstractmethod
      def read_text(self, filename):
          """Attempt to load metadata file given by the name.
  
          :param filename: The name of the file in the distribution info.
          :return: The text if found, otherwise None.
          """
  
      @abc.abstractmethod
      def locate_file(self, path):
          """
          Given a path to a file in this distribution, return a path
          to it.
          """
  
      @classmethod
      def from_name(cls, name):
          """Return the Distribution for the given package name.
  
          :param name: The name of the distribution package to search for.
          :return: The Distribution instance (or subclass thereof) for the named
              package, if found.
          :raises PackageNotFoundError: When the named package's distribution
              metadata cannot be found.
          """
          for resolver in cls._discover_resolvers():
              dists = resolver(DistributionFinder.Context(name=name))
              dist = next(iter(dists), None)
              if dist is not None:
                  return dist
          else:
              raise PackageNotFoundError(name)
  
      @classmethod
      def discover(cls, **kwargs):
          """Return an iterable of Distribution objects for all packages.
  
          Pass a ``context`` or pass keyword arguments for constructing
          a context.
  
          :context: A ``DistributionFinder.Context`` object.
          :return: Iterable of Distribution objects for all packages.
          """
          context = kwargs.pop('context', None)
          if context and kwargs:
              raise ValueError("cannot accept context and kwargs")
          context = context or DistributionFinder.Context(**kwargs)
          return itertools.chain.from_iterable(
              resolver(context)
              for resolver in cls._discover_resolvers()
              )
  
      @staticmethod
      def at(path):
          """Return a Distribution for the indicated metadata path
  
          :param path: a string or path-like object
          :return: a concrete Distribution instance for the path
          """
          return PathDistribution(pathlib.Path(path))
  
      @staticmethod
      def _discover_resolvers():
          """Search the meta_path for resolvers."""
          declared = (
              getattr(finder, 'find_distributions', None)
              for finder in sys.meta_path
              )
          return filter(None, declared)
  
      @classmethod
      def _local(cls, root='.'):
          from pep517 import build, meta
          system = build.compat_system(root)
          builder = functools.partial(
              meta.build,
              source_dir=root,
              system=system,
              )
          return PathDistribution(zipfile.Path(meta.build_as_zip(builder)))
  
      @property
      def metadata(self):
          """Return the parsed metadata for this Distribution.
  
          The returned object will have keys that name the various bits of
          metadata.  See PEP 566 for details.
          """
          text = (
              self.read_text('METADATA')
              or self.read_text('PKG-INFO')
              # This last clause is here to support old egg-info files.  Its
              # effect is to just end up using the PathDistribution's self._path
              # (which points to the egg-info file) attribute unchanged.
              or self.read_text('')
              )
          return email.message_from_string(text)
  
      @property
      def version(self):
          """Return the 'Version' metadata for the distribution package."""
          return self.metadata['Version']
  
      @property
      def entry_points(self):
          return EntryPoint._from_text(self.read_text('entry_points.txt'))
  
      @property
      def files(self):
          """Files in this distribution.
  
          :return: List of PackagePath for this distribution or None
  
          Result is `None` if the metadata file that enumerates files
          (i.e. RECORD for dist-info or SOURCES.txt for egg-info) is
          missing.
          Result may be empty if the metadata exists but is empty.
          """
          file_lines = self._read_files_distinfo() or self._read_files_egginfo()
  
          def make_file(name, hash=None, size_str=None):
              result = PackagePath(name)
              result.hash = FileHash(hash) if hash else None
              result.size = int(size_str) if size_str else None
              result.dist = self
              return result
  
          return file_lines and list(starmap(make_file, csv.reader(file_lines)))
  
      def _read_files_distinfo(self):
          """
          Read the lines of RECORD
          """
          text = self.read_text('RECORD')
          return text and text.splitlines()
  
      def _read_files_egginfo(self):
          """
          SOURCES.txt might contain literal commas, so wrap each line
          in quotes.
          """
          text = self.read_text('SOURCES.txt')
          return text and map('"{}"'.format, text.splitlines())
  
      @property
      def requires(self):
          """Generated requirements specified for this Distribution"""
          reqs = self._read_dist_info_reqs() or self._read_egg_info_reqs()
          return reqs and list(reqs)
  
      def _read_dist_info_reqs(self):
          return self.metadata.get_all('Requires-Dist')
  
      def _read_egg_info_reqs(self):
          source = self.read_text('requires.txt')
          return source and self._deps_from_requires_text(source)
  
      @classmethod
      def _deps_from_requires_text(cls, source):
          section_pairs = cls._read_sections(source.splitlines())
          sections = {
              section: list(map(operator.itemgetter('line'), results))
              for section, results in
              itertools.groupby(section_pairs, operator.itemgetter('section'))
              }
          return cls._convert_egg_info_reqs_to_simple_reqs(sections)
  
      @staticmethod
      def _read_sections(lines):
          section = None
          for line in filter(None, lines):
              section_match = re.match(r'\[(.*)\]$', line)
              if section_match:
                  section = section_match.group(1)
                  continue
              yield locals()
  
      @staticmethod
      def _convert_egg_info_reqs_to_simple_reqs(sections):
          """
          Historically, setuptools would solicit and store 'extra'
          requirements, including those with environment markers,
          in separate sections. More modern tools expect each
          dependency to be defined separately, with any relevant
          extras and environment markers attached directly to that
          requirement. This method converts the former to the
          latter. See _test_deps_from_requires_text for an example.
          """
          def make_condition(name):
              return name and 'extra == "{name}"'.format(name=name)
  
          def parse_condition(section):
              section = section or ''
              extra, sep, markers = section.partition(':')
              if extra and markers:
                  markers = '({markers})'.format(markers=markers)
              conditions = list(filter(None, [markers, make_condition(extra)]))
              return '; ' + ' and '.join(conditions) if conditions else ''
  
          for section, deps in sections.items():
              for dep in deps:
                  yield dep + parse_condition(section)
  
  
  class DistributionFinder(MetaPathFinder):
      """
      A MetaPathFinder capable of discovering installed distributions.
      """
  
      class Context:
          """
          Keyword arguments presented by the caller to
          ``distributions()`` or ``Distribution.discover()``
          to narrow the scope of a search for distributions
          in all DistributionFinders.
  
          Each DistributionFinder may expect any parameters
          and should attempt to honor the canonical
          parameters defined below when appropriate.
          """
  
          name = None
          """
          Specific name for which a distribution finder should match.
          A name of ``None`` matches all distributions.
          """
  
          def __init__(self, **kwargs):
              vars(self).update(kwargs)
  
          @property
          def path(self):
              """
              The path that a distribution finder should search.
  
              Typically refers to Python package paths and defaults
              to ``sys.path``.
              """
              return vars(self).get('path', sys.path)
  
      @abc.abstractmethod
      def find_distributions(self, context=Context()):
          """
          Find distributions.
  
          Return an iterable of all Distribution instances capable of
          loading the metadata for packages matching the ``context``,
          a DistributionFinder.Context instance.
          """
  
  
  class FastPath:
      """
      Micro-optimized class for searching a path for
      children.
      """
  
      def __init__(self, root):
          self.root = root
          self.base = os.path.basename(self.root).lower()
  
      def joinpath(self, child):
          return pathlib.Path(self.root, child)
  
      def children(self):
          with suppress(Exception):
              return os.listdir(self.root or '')
          with suppress(Exception):
              return self.zip_children()
          return []
  
      def zip_children(self):
          zip_path = zipfile.Path(self.root)
          names = zip_path.root.namelist()
          self.joinpath = zip_path.joinpath
  
          return dict.fromkeys(
              child.split(posixpath.sep, 1)[0]
              for child in names
              )
  
      def is_egg(self, search):
          base = self.base
          return (
              base == search.versionless_egg_name
              or base.startswith(search.prefix)
              and base.endswith('.egg'))
  
      def search(self, name):
          for child in self.children():
              n_low = child.lower()
              if (n_low in name.exact_matches
                      or n_low.startswith(name.prefix)
                      and n_low.endswith(name.suffixes)
                      # legacy case:
                      or self.is_egg(name) and n_low == 'egg-info'):
                  yield self.joinpath(child)
  
  
  class Prepared:
      """
      A prepared search for metadata on a possibly-named package.
      """
      normalized = ''
      prefix = ''
      suffixes = '.dist-info', '.egg-info'
      exact_matches = [''][:0]
      versionless_egg_name = ''
  
      def __init__(self, name):
          self.name = name
          if name is None:
              return
          self.normalized = name.lower().replace('-', '_')
          self.prefix = self.normalized + '-'
          self.exact_matches = [
              self.normalized + suffix for suffix in self.suffixes]
          self.versionless_egg_name = self.normalized + '.egg'
  
  
  class MetadataPathFinder(DistributionFinder):
      @classmethod
      def find_distributions(cls, context=DistributionFinder.Context()):
          """
          Find distributions.
  
          Return an iterable of all Distribution instances capable of
          loading the metadata for packages matching ``context.name``
          (or all names if ``None`` indicated) along the paths in the list
          of directories ``context.path``.
          """
          found = cls._search_paths(context.name, context.path)
          return map(PathDistribution, found)
  
      @classmethod
      def _search_paths(cls, name, paths):
          """Find metadata directories in paths heuristically."""
          return itertools.chain.from_iterable(
              path.search(Prepared(name))
              for path in map(FastPath, paths)
              )
  
  
  class PathDistribution(Distribution):
      def __init__(self, path):
          """Construct a distribution from a path to the metadata directory.
  
          :param path: A pathlib.Path or similar object supporting
                       .joinpath(), __div__, .parent, and .read_text().
          """
          self._path = path
  
      def read_text(self, filename):
          with suppress(FileNotFoundError, IsADirectoryError, KeyError,
                        NotADirectoryError, PermissionError):
              return self._path.joinpath(filename).read_text(encoding='utf-8')
      read_text.__doc__ = Distribution.read_text.__doc__
  
      def locate_file(self, path):
          return self._path.parent / path
  
  
  def distribution(distribution_name):
      """Get the ``Distribution`` instance for the named package.
  
      :param distribution_name: The name of the distribution package as a string.
      :return: A ``Distribution`` instance (or subclass thereof).
      """
      return Distribution.from_name(distribution_name)
  
  
  def distributions(**kwargs):
      """Get all ``Distribution`` instances in the current environment.
  
      :return: An iterable of ``Distribution`` instances.
      """
      return Distribution.discover(**kwargs)
  
  
  def metadata(distribution_name):
      """Get the metadata for the named package.
  
      :param distribution_name: The name of the distribution package to query.
      :return: An email.Message containing the parsed metadata.
      """
      return Distribution.from_name(distribution_name).metadata
  
  
  def version(distribution_name):
      """Get the version string for the named package.
  
      :param distribution_name: The name of the distribution package to query.
      :return: The version string for the package as defined in the package's
          "Version" metadata key.
      """
      return distribution(distribution_name).version
  
  
  def entry_points():
      """Return EntryPoint objects for all installed packages.
  
      :return: EntryPoint objects for all installed packages.
      """
      eps = itertools.chain.from_iterable(
          dist.entry_points for dist in distributions())
      by_group = operator.attrgetter('group')
      ordered = sorted(eps, key=by_group)
      grouped = itertools.groupby(ordered, by_group)
      return {
          group: tuple(eps)
          for group, eps in grouped
          }
  
  
  def files(distribution_name):
      """Return a list of files for the named package.
  
      :param distribution_name: The name of the distribution package to query.
      :return: List of files composing the distribution.
      """
      return distribution(distribution_name).files
  
  
  def requires(distribution_name):
      """
      Return a list of requirements for the named package.
  
      :return: An iterator of requirements, suitable for
      packaging.requirement.Requirement.
      """
      return distribution(distribution_name).requires
  