--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/env/lib/python3.7/site-packages/distlib/metadata.py	Sat May 02 07:14:21 2020 -0400
@@ -0,0 +1,1096 @@
+# -*- coding: utf-8 -*-
+#
+# Copyright (C) 2012 The Python Software Foundation.
+# See LICENSE.txt and CONTRIBUTORS.txt.
+#
+"""Implementation of the Metadata for Python packages PEPs.
+
+Supports all metadata formats (1.0, 1.1, 1.2, and 2.0 experimental).
+"""
+from __future__ import unicode_literals
+
+import codecs
+from email import message_from_file
+import json
+import logging
+import re
+
+
+from . import DistlibException, __version__
+from .compat import StringIO, string_types, text_type
+from .markers import interpret
+from .util import extract_by_key, get_extras
+from .version import get_scheme, PEP440_VERSION_RE
+
+logger = logging.getLogger(__name__)
+
+
+class MetadataMissingError(DistlibException):
+    """A required metadata is missing"""
+
+
+class MetadataConflictError(DistlibException):
+    """Attempt to read or write metadata fields that are conflictual."""
+
+
+class MetadataUnrecognizedVersionError(DistlibException):
+    """Unknown metadata version number."""
+
+
+class MetadataInvalidError(DistlibException):
+    """A metadata value is invalid"""
+
+# public API of this module
+__all__ = ['Metadata', 'PKG_INFO_ENCODING', 'PKG_INFO_PREFERRED_VERSION']
+
+# Encoding used for the PKG-INFO files
+PKG_INFO_ENCODING = 'utf-8'
+
+# preferred version. Hopefully will be changed
+# to 1.2 once PEP 345 is supported everywhere
+PKG_INFO_PREFERRED_VERSION = '1.1'
+
+_LINE_PREFIX_1_2 = re.compile('\n       \\|')
+_LINE_PREFIX_PRE_1_2 = re.compile('\n        ')
+_241_FIELDS = ('Metadata-Version', 'Name', 'Version', 'Platform',
+               'Summary', 'Description',
+               'Keywords', 'Home-page', 'Author', 'Author-email',
+               'License')
+
+_314_FIELDS = ('Metadata-Version', 'Name', 'Version', 'Platform',
+               'Supported-Platform', 'Summary', 'Description',
+               'Keywords', 'Home-page', 'Author', 'Author-email',
+               'License', 'Classifier', 'Download-URL', 'Obsoletes',
+               'Provides', 'Requires')
+
+_314_MARKERS = ('Obsoletes', 'Provides', 'Requires', 'Classifier',
+                'Download-URL')
+
+_345_FIELDS = ('Metadata-Version', 'Name', 'Version', 'Platform',
+               'Supported-Platform', 'Summary', 'Description',
+               'Keywords', 'Home-page', 'Author', 'Author-email',
+               'Maintainer', 'Maintainer-email', 'License',
+               'Classifier', 'Download-URL', 'Obsoletes-Dist',
+               'Project-URL', 'Provides-Dist', 'Requires-Dist',
+               'Requires-Python', 'Requires-External')
+
+_345_MARKERS = ('Provides-Dist', 'Requires-Dist', 'Requires-Python',
+                'Obsoletes-Dist', 'Requires-External', 'Maintainer',
+                'Maintainer-email', 'Project-URL')
+
+_426_FIELDS = ('Metadata-Version', 'Name', 'Version', 'Platform',
+               'Supported-Platform', 'Summary', 'Description',
+               'Keywords', 'Home-page', 'Author', 'Author-email',
+               'Maintainer', 'Maintainer-email', 'License',
+               'Classifier', 'Download-URL', 'Obsoletes-Dist',
+               'Project-URL', 'Provides-Dist', 'Requires-Dist',
+               'Requires-Python', 'Requires-External', 'Private-Version',
+               'Obsoleted-By', 'Setup-Requires-Dist', 'Extension',
+               'Provides-Extra')
+
+_426_MARKERS = ('Private-Version', 'Provides-Extra', 'Obsoleted-By',
+                'Setup-Requires-Dist', 'Extension')
+
+# See issue #106: Sometimes 'Requires' and 'Provides' occur wrongly in
+# the metadata. Include them in the tuple literal below to allow them
+# (for now).
+_566_FIELDS = _426_FIELDS + ('Description-Content-Type',
+                             'Requires', 'Provides')
+
+_566_MARKERS = ('Description-Content-Type',)
+
+_ALL_FIELDS = set()
+_ALL_FIELDS.update(_241_FIELDS)
+_ALL_FIELDS.update(_314_FIELDS)
+_ALL_FIELDS.update(_345_FIELDS)
+_ALL_FIELDS.update(_426_FIELDS)
+_ALL_FIELDS.update(_566_FIELDS)
+
+EXTRA_RE = re.compile(r'''extra\s*==\s*("([^"]+)"|'([^']+)')''')
+
+
+def _version2fieldlist(version):
+    if version == '1.0':
+        return _241_FIELDS
+    elif version == '1.1':
+        return _314_FIELDS
+    elif version == '1.2':
+        return _345_FIELDS
+    elif version in ('1.3', '2.1'):
+        return _345_FIELDS + _566_FIELDS
+    elif version == '2.0':
+        return _426_FIELDS
+    raise MetadataUnrecognizedVersionError(version)
+
+
+def _best_version(fields):
+    """Detect the best version depending on the fields used."""
+    def _has_marker(keys, markers):
+        for marker in markers:
+            if marker in keys:
+                return True
+        return False
+
+    keys = []
+    for key, value in fields.items():
+        if value in ([], 'UNKNOWN', None):
+            continue
+        keys.append(key)
+
+    possible_versions = ['1.0', '1.1', '1.2', '1.3', '2.0', '2.1']
+
+    # first let's try to see if a field is not part of one of the version
+    for key in keys:
+        if key not in _241_FIELDS and '1.0' in possible_versions:
+            possible_versions.remove('1.0')
+            logger.debug('Removed 1.0 due to %s', key)
+        if key not in _314_FIELDS and '1.1' in possible_versions:
+            possible_versions.remove('1.1')
+            logger.debug('Removed 1.1 due to %s', key)
+        if key not in _345_FIELDS and '1.2' in possible_versions:
+            possible_versions.remove('1.2')
+            logger.debug('Removed 1.2 due to %s', key)
+        if key not in _566_FIELDS and '1.3' in possible_versions:
+            possible_versions.remove('1.3')
+            logger.debug('Removed 1.3 due to %s', key)
+        if key not in _566_FIELDS and '2.1' in possible_versions:
+            if key != 'Description':  # In 2.1, description allowed after headers
+                possible_versions.remove('2.1')
+                logger.debug('Removed 2.1 due to %s', key)
+        if key not in _426_FIELDS and '2.0' in possible_versions:
+            possible_versions.remove('2.0')
+            logger.debug('Removed 2.0 due to %s', key)
+
+    # possible_version contains qualified versions
+    if len(possible_versions) == 1:
+        return possible_versions[0]   # found !
+    elif len(possible_versions) == 0:
+        logger.debug('Out of options - unknown metadata set: %s', fields)
+        raise MetadataConflictError('Unknown metadata set')
+
+    # let's see if one unique marker is found
+    is_1_1 = '1.1' in possible_versions and _has_marker(keys, _314_MARKERS)
+    is_1_2 = '1.2' in possible_versions and _has_marker(keys, _345_MARKERS)
+    is_2_1 = '2.1' in possible_versions and _has_marker(keys, _566_MARKERS)
+    is_2_0 = '2.0' in possible_versions and _has_marker(keys, _426_MARKERS)
+    if int(is_1_1) + int(is_1_2) + int(is_2_1) + int(is_2_0) > 1:
+        raise MetadataConflictError('You used incompatible 1.1/1.2/2.0/2.1 fields')
+
+    # we have the choice, 1.0, or 1.2, or 2.0
+    #   - 1.0 has a broken Summary field but works with all tools
+    #   - 1.1 is to avoid
+    #   - 1.2 fixes Summary but has little adoption
+    #   - 2.0 adds more features and is very new
+    if not is_1_1 and not is_1_2 and not is_2_1 and not is_2_0:
+        # we couldn't find any specific marker
+        if PKG_INFO_PREFERRED_VERSION in possible_versions:
+            return PKG_INFO_PREFERRED_VERSION
+    if is_1_1:
+        return '1.1'
+    if is_1_2:
+        return '1.2'
+    if is_2_1:
+        return '2.1'
+
+    return '2.0'
+
+_ATTR2FIELD = {
+    'metadata_version': 'Metadata-Version',
+    'name': 'Name',
+    'version': 'Version',
+    'platform': 'Platform',
+    'supported_platform': 'Supported-Platform',
+    'summary': 'Summary',
+    'description': 'Description',
+    'keywords': 'Keywords',
+    'home_page': 'Home-page',
+    'author': 'Author',
+    'author_email': 'Author-email',
+    'maintainer': 'Maintainer',
+    'maintainer_email': 'Maintainer-email',
+    'license': 'License',
+    'classifier': 'Classifier',
+    'download_url': 'Download-URL',
+    'obsoletes_dist': 'Obsoletes-Dist',
+    'provides_dist': 'Provides-Dist',
+    'requires_dist': 'Requires-Dist',
+    'setup_requires_dist': 'Setup-Requires-Dist',
+    'requires_python': 'Requires-Python',
+    'requires_external': 'Requires-External',
+    'requires': 'Requires',
+    'provides': 'Provides',
+    'obsoletes': 'Obsoletes',
+    'project_url': 'Project-URL',
+    'private_version': 'Private-Version',
+    'obsoleted_by': 'Obsoleted-By',
+    'extension': 'Extension',
+    'provides_extra': 'Provides-Extra',
+}
+
+_PREDICATE_FIELDS = ('Requires-Dist', 'Obsoletes-Dist', 'Provides-Dist')
+_VERSIONS_FIELDS = ('Requires-Python',)
+_VERSION_FIELDS = ('Version',)
+_LISTFIELDS = ('Platform', 'Classifier', 'Obsoletes',
+               'Requires', 'Provides', 'Obsoletes-Dist',
+               'Provides-Dist', 'Requires-Dist', 'Requires-External',
+               'Project-URL', 'Supported-Platform', 'Setup-Requires-Dist',
+               'Provides-Extra', 'Extension')
+_LISTTUPLEFIELDS = ('Project-URL',)
+
+_ELEMENTSFIELD = ('Keywords',)
+
+_UNICODEFIELDS = ('Author', 'Maintainer', 'Summary', 'Description')
+
+_MISSING = object()
+
+_FILESAFE = re.compile('[^A-Za-z0-9.]+')
+
+
+def _get_name_and_version(name, version, for_filename=False):
+    """Return the distribution name with version.
+
+    If for_filename is true, return a filename-escaped form."""
+    if for_filename:
+        # For both name and version any runs of non-alphanumeric or '.'
+        # characters are replaced with a single '-'.  Additionally any
+        # spaces in the version string become '.'
+        name = _FILESAFE.sub('-', name)
+        version = _FILESAFE.sub('-', version.replace(' ', '.'))
+    return '%s-%s' % (name, version)
+
+
+class LegacyMetadata(object):
+    """The legacy metadata of a release.
+
+    Supports versions 1.0, 1.1 and 1.2 (auto-detected). You can
+    instantiate the class with one of these arguments (or none):
+    - *path*, the path to a metadata file
+    - *fileobj* give a file-like object with metadata as content
+    - *mapping* is a dict-like object
+    - *scheme* is a version scheme name
+    """
+    # TODO document the mapping API and UNKNOWN default key
+
+    def __init__(self, path=None, fileobj=None, mapping=None,
+                 scheme='default'):
+        if [path, fileobj, mapping].count(None) < 2:
+            raise TypeError('path, fileobj and mapping are exclusive')
+        self._fields = {}
+        self.requires_files = []
+        self._dependencies = None
+        self.scheme = scheme
+        if path is not None:
+            self.read(path)
+        elif fileobj is not None:
+            self.read_file(fileobj)
+        elif mapping is not None:
+            self.update(mapping)
+            self.set_metadata_version()
+
+    def set_metadata_version(self):
+        self._fields['Metadata-Version'] = _best_version(self._fields)
+
+    def _write_field(self, fileobj, name, value):
+        fileobj.write('%s: %s\n' % (name, value))
+
+    def __getitem__(self, name):
+        return self.get(name)
+
+    def __setitem__(self, name, value):
+        return self.set(name, value)
+
+    def __delitem__(self, name):
+        field_name = self._convert_name(name)
+        try:
+            del self._fields[field_name]
+        except KeyError:
+            raise KeyError(name)
+
+    def __contains__(self, name):
+        return (name in self._fields or
+                self._convert_name(name) in self._fields)
+
+    def _convert_name(self, name):
+        if name in _ALL_FIELDS:
+            return name
+        name = name.replace('-', '_').lower()
+        return _ATTR2FIELD.get(name, name)
+
+    def _default_value(self, name):
+        if name in _LISTFIELDS or name in _ELEMENTSFIELD:
+            return []
+        return 'UNKNOWN'
+
+    def _remove_line_prefix(self, value):
+        if self.metadata_version in ('1.0', '1.1'):
+            return _LINE_PREFIX_PRE_1_2.sub('\n', value)
+        else:
+            return _LINE_PREFIX_1_2.sub('\n', value)
+
+    def __getattr__(self, name):
+        if name in _ATTR2FIELD:
+            return self[name]
+        raise AttributeError(name)
+
+    #
+    # Public API
+    #
+
+#    dependencies = property(_get_dependencies, _set_dependencies)
+
+    def get_fullname(self, filesafe=False):
+        """Return the distribution name with version.
+
+        If filesafe is true, return a filename-escaped form."""
+        return _get_name_and_version(self['Name'], self['Version'], filesafe)
+
+    def is_field(self, name):
+        """return True if name is a valid metadata key"""
+        name = self._convert_name(name)
+        return name in _ALL_FIELDS
+
+    def is_multi_field(self, name):
+        name = self._convert_name(name)
+        return name in _LISTFIELDS
+
+    def read(self, filepath):
+        """Read the metadata values from a file path."""
+        fp = codecs.open(filepath, 'r', encoding='utf-8')
+        try:
+            self.read_file(fp)
+        finally:
+            fp.close()
+
+    def read_file(self, fileob):
+        """Read the metadata values from a file object."""
+        msg = message_from_file(fileob)
+        self._fields['Metadata-Version'] = msg['metadata-version']
+
+        # When reading, get all the fields we can
+        for field in _ALL_FIELDS:
+            if field not in msg:
+                continue
+            if field in _LISTFIELDS:
+                # we can have multiple lines
+                values = msg.get_all(field)
+                if field in _LISTTUPLEFIELDS and values is not None:
+                    values = [tuple(value.split(',')) for value in values]
+                self.set(field, values)
+            else:
+                # single line
+                value = msg[field]
+                if value is not None and value != 'UNKNOWN':
+                    self.set(field, value)
+        # logger.debug('Attempting to set metadata for %s', self)
+        # self.set_metadata_version()
+
+    def write(self, filepath, skip_unknown=False):
+        """Write the metadata fields to filepath."""
+        fp = codecs.open(filepath, 'w', encoding='utf-8')
+        try:
+            self.write_file(fp, skip_unknown)
+        finally:
+            fp.close()
+
+    def write_file(self, fileobject, skip_unknown=False):
+        """Write the PKG-INFO format data to a file object."""
+        self.set_metadata_version()
+
+        for field in _version2fieldlist(self['Metadata-Version']):
+            values = self.get(field)
+            if skip_unknown and values in ('UNKNOWN', [], ['UNKNOWN']):
+                continue
+            if field in _ELEMENTSFIELD:
+                self._write_field(fileobject, field, ','.join(values))
+                continue
+            if field not in _LISTFIELDS:
+                if field == 'Description':
+                    if self.metadata_version in ('1.0', '1.1'):
+                        values = values.replace('\n', '\n        ')
+                    else:
+                        values = values.replace('\n', '\n       |')
+                values = [values]
+
+            if field in _LISTTUPLEFIELDS:
+                values = [','.join(value) for value in values]
+
+            for value in values:
+                self._write_field(fileobject, field, value)
+
+    def update(self, other=None, **kwargs):
+        """Set metadata values from the given iterable `other` and kwargs.
+
+        Behavior is like `dict.update`: If `other` has a ``keys`` method,
+        they are looped over and ``self[key]`` is assigned ``other[key]``.
+        Else, ``other`` is an iterable of ``(key, value)`` iterables.
+
+        Keys that don't match a metadata field or that have an empty value are
+        dropped.
+        """
+        def _set(key, value):
+            if key in _ATTR2FIELD and value:
+                self.set(self._convert_name(key), value)
+
+        if not other:
+            # other is None or empty container
+            pass
+        elif hasattr(other, 'keys'):
+            for k in other.keys():
+                _set(k, other[k])
+        else:
+            for k, v in other:
+                _set(k, v)
+
+        if kwargs:
+            for k, v in kwargs.items():
+                _set(k, v)
+
+    def set(self, name, value):
+        """Control then set a metadata field."""
+        name = self._convert_name(name)
+
+        if ((name in _ELEMENTSFIELD or name == 'Platform') and
+            not isinstance(value, (list, tuple))):
+            if isinstance(value, string_types):
+                value = [v.strip() for v in value.split(',')]
+            else:
+                value = []
+        elif (name in _LISTFIELDS and
+              not isinstance(value, (list, tuple))):
+            if isinstance(value, string_types):
+                value = [value]
+            else:
+                value = []
+
+        if logger.isEnabledFor(logging.WARNING):
+            project_name = self['Name']
+
+            scheme = get_scheme(self.scheme)
+            if name in _PREDICATE_FIELDS and value is not None:
+                for v in value:
+                    # check that the values are valid
+                    if not scheme.is_valid_matcher(v.split(';')[0]):
+                        logger.warning(
+                            "'%s': '%s' is not valid (field '%s')",
+                            project_name, v, name)
+            # FIXME this rejects UNKNOWN, is that right?
+            elif name in _VERSIONS_FIELDS and value is not None:
+                if not scheme.is_valid_constraint_list(value):
+                    logger.warning("'%s': '%s' is not a valid version (field '%s')",
+                                   project_name, value, name)
+            elif name in _VERSION_FIELDS and value is not None:
+                if not scheme.is_valid_version(value):
+                    logger.warning("'%s': '%s' is not a valid version (field '%s')",
+                                   project_name, value, name)
+
+        if name in _UNICODEFIELDS:
+            if name == 'Description':
+                value = self._remove_line_prefix(value)
+
+        self._fields[name] = value
+
+    def get(self, name, default=_MISSING):
+        """Get a metadata field."""
+        name = self._convert_name(name)
+        if name not in self._fields:
+            if default is _MISSING:
+                default = self._default_value(name)
+            return default
+        if name in _UNICODEFIELDS:
+            value = self._fields[name]
+            return value
+        elif name in _LISTFIELDS:
+            value = self._fields[name]
+            if value is None:
+                return []
+            res = []
+            for val in value:
+                if name not in _LISTTUPLEFIELDS:
+                    res.append(val)
+                else:
+                    # That's for Project-URL
+                    res.append((val[0], val[1]))
+            return res
+
+        elif name in _ELEMENTSFIELD:
+            value = self._fields[name]
+            if isinstance(value, string_types):
+                return value.split(',')
+        return self._fields[name]
+
+    def check(self, strict=False):
+        """Check if the metadata is compliant. If strict is True then raise if
+        no Name or Version are provided"""
+        self.set_metadata_version()
+
+        # XXX should check the versions (if the file was loaded)
+        missing, warnings = [], []
+
+        for attr in ('Name', 'Version'):  # required by PEP 345
+            if attr not in self:
+                missing.append(attr)
+
+        if strict and missing != []:
+            msg = 'missing required metadata: %s' % ', '.join(missing)
+            raise MetadataMissingError(msg)
+
+        for attr in ('Home-page', 'Author'):
+            if attr not in self:
+                missing.append(attr)
+
+        # checking metadata 1.2 (XXX needs to check 1.1, 1.0)
+        if self['Metadata-Version'] != '1.2':
+            return missing, warnings
+
+        scheme = get_scheme(self.scheme)
+
+        def are_valid_constraints(value):
+            for v in value:
+                if not scheme.is_valid_matcher(v.split(';')[0]):
+                    return False
+            return True
+
+        for fields, controller in ((_PREDICATE_FIELDS, are_valid_constraints),
+                                   (_VERSIONS_FIELDS,
+                                    scheme.is_valid_constraint_list),
+                                   (_VERSION_FIELDS,
+                                    scheme.is_valid_version)):
+            for field in fields:
+                value = self.get(field, None)
+                if value is not None and not controller(value):
+                    warnings.append("Wrong value for '%s': %s" % (field, value))
+
+        return missing, warnings
+
+    def todict(self, skip_missing=False):
+        """Return fields as a dict.
+
+        Field names will be converted to use the underscore-lowercase style
+        instead of hyphen-mixed case (i.e. home_page instead of Home-page).
+        """
+        self.set_metadata_version()
+
+        mapping_1_0 = (
+            ('metadata_version', 'Metadata-Version'),
+            ('name', 'Name'),
+            ('version', 'Version'),
+            ('summary', 'Summary'),
+            ('home_page', 'Home-page'),
+            ('author', 'Author'),
+            ('author_email', 'Author-email'),
+            ('license', 'License'),
+            ('description', 'Description'),
+            ('keywords', 'Keywords'),
+            ('platform', 'Platform'),
+            ('classifiers', 'Classifier'),
+            ('download_url', 'Download-URL'),
+        )
+
+        data = {}
+        for key, field_name in mapping_1_0:
+            if not skip_missing or field_name in self._fields:
+                data[key] = self[field_name]
+
+        if self['Metadata-Version'] == '1.2':
+            mapping_1_2 = (
+                ('requires_dist', 'Requires-Dist'),
+                ('requires_python', 'Requires-Python'),
+                ('requires_external', 'Requires-External'),
+                ('provides_dist', 'Provides-Dist'),
+                ('obsoletes_dist', 'Obsoletes-Dist'),
+                ('project_url', 'Project-URL'),
+                ('maintainer', 'Maintainer'),
+                ('maintainer_email', 'Maintainer-email'),
+            )
+            for key, field_name in mapping_1_2:
+                if not skip_missing or field_name in self._fields:
+                    if key != 'project_url':
+                        data[key] = self[field_name]
+                    else:
+                        data[key] = [','.join(u) for u in self[field_name]]
+
+        elif self['Metadata-Version'] == '1.1':
+            mapping_1_1 = (
+                ('provides', 'Provides'),
+                ('requires', 'Requires'),
+                ('obsoletes', 'Obsoletes'),
+            )
+            for key, field_name in mapping_1_1:
+                if not skip_missing or field_name in self._fields:
+                    data[key] = self[field_name]
+
+        return data
+
+    def add_requirements(self, requirements):
+        if self['Metadata-Version'] == '1.1':
+            # we can't have 1.1 metadata *and* Setuptools requires
+            for field in ('Obsoletes', 'Requires', 'Provides'):
+                if field in self:
+                    del self[field]
+        self['Requires-Dist'] += requirements
+
+    # Mapping API
+    # TODO could add iter* variants
+
+    def keys(self):
+        return list(_version2fieldlist(self['Metadata-Version']))
+
+    def __iter__(self):
+        for key in self.keys():
+            yield key
+
+    def values(self):
+        return [self[key] for key in self.keys()]
+
+    def items(self):
+        return [(key, self[key]) for key in self.keys()]
+
+    def __repr__(self):
+        return '<%s %s %s>' % (self.__class__.__name__, self.name,
+                               self.version)
+
+
+METADATA_FILENAME = 'pydist.json'
+WHEEL_METADATA_FILENAME = 'metadata.json'
+LEGACY_METADATA_FILENAME = 'METADATA'
+
+
+class Metadata(object):
+    """
+    The metadata of a release. This implementation uses 2.0 (JSON)
+    metadata where possible. If not possible, it wraps a LegacyMetadata
+    instance which handles the key-value metadata format.
+    """
+
+    METADATA_VERSION_MATCHER = re.compile(r'^\d+(\.\d+)*$')
+
+    NAME_MATCHER = re.compile('^[0-9A-Z]([0-9A-Z_.-]*[0-9A-Z])?$', re.I)
+
+    VERSION_MATCHER = PEP440_VERSION_RE
+
+    SUMMARY_MATCHER = re.compile('.{1,2047}')
+
+    METADATA_VERSION = '2.0'
+
+    GENERATOR = 'distlib (%s)' % __version__
+
+    MANDATORY_KEYS = {
+        'name': (),
+        'version': (),
+        'summary': ('legacy',),
+    }
+
+    INDEX_KEYS = ('name version license summary description author '
+                  'author_email keywords platform home_page classifiers '
+                  'download_url')
+
+    DEPENDENCY_KEYS = ('extras run_requires test_requires build_requires '
+                       'dev_requires provides meta_requires obsoleted_by '
+                       'supports_environments')
+
+    SYNTAX_VALIDATORS = {
+        'metadata_version': (METADATA_VERSION_MATCHER, ()),
+        'name': (NAME_MATCHER, ('legacy',)),
+        'version': (VERSION_MATCHER, ('legacy',)),
+        'summary': (SUMMARY_MATCHER, ('legacy',)),
+    }
+
+    __slots__ = ('_legacy', '_data', 'scheme')
+
+    def __init__(self, path=None, fileobj=None, mapping=None,
+                 scheme='default'):
+        if [path, fileobj, mapping].count(None) < 2:
+            raise TypeError('path, fileobj and mapping are exclusive')
+        self._legacy = None
+        self._data = None
+        self.scheme = scheme
+        #import pdb; pdb.set_trace()
+        if mapping is not None:
+            try:
+                self._validate_mapping(mapping, scheme)
+                self._data = mapping
+            except MetadataUnrecognizedVersionError:
+                self._legacy = LegacyMetadata(mapping=mapping, scheme=scheme)
+                self.validate()
+        else:
+            data = None
+            if path:
+                with open(path, 'rb') as f:
+                    data = f.read()
+            elif fileobj:
+                data = fileobj.read()
+            if data is None:
+                # Initialised with no args - to be added
+                self._data = {
+                    'metadata_version': self.METADATA_VERSION,
+                    'generator': self.GENERATOR,
+                }
+            else:
+                if not isinstance(data, text_type):
+                    data = data.decode('utf-8')
+                try:
+                    self._data = json.loads(data)
+                    self._validate_mapping(self._data, scheme)
+                except ValueError:
+                    # Note: MetadataUnrecognizedVersionError does not
+                    # inherit from ValueError (it's a DistlibException,
+                    # which should not inherit from ValueError).
+                    # The ValueError comes from the json.load - if that
+                    # succeeds and we get a validation error, we want
+                    # that to propagate
+                    self._legacy = LegacyMetadata(fileobj=StringIO(data),
+                                                  scheme=scheme)
+                    self.validate()
+
+    common_keys = set(('name', 'version', 'license', 'keywords', 'summary'))
+
+    none_list = (None, list)
+    none_dict = (None, dict)
+
+    mapped_keys = {
+        'run_requires': ('Requires-Dist', list),
+        'build_requires': ('Setup-Requires-Dist', list),
+        'dev_requires': none_list,
+        'test_requires': none_list,
+        'meta_requires': none_list,
+        'extras': ('Provides-Extra', list),
+        'modules': none_list,
+        'namespaces': none_list,
+        'exports': none_dict,
+        'commands': none_dict,
+        'classifiers': ('Classifier', list),
+        'source_url': ('Download-URL', None),
+        'metadata_version': ('Metadata-Version', None),
+    }
+
+    del none_list, none_dict
+
+    def __getattribute__(self, key):
+        common = object.__getattribute__(self, 'common_keys')
+        mapped = object.__getattribute__(self, 'mapped_keys')
+        if key in mapped:
+            lk, maker = mapped[key]
+            if self._legacy:
+                if lk is None:
+                    result = None if maker is None else maker()
+                else:
+                    result = self._legacy.get(lk)
+            else:
+                value = None if maker is None else maker()
+                if key not in ('commands', 'exports', 'modules', 'namespaces',
+                               'classifiers'):
+                    result = self._data.get(key, value)
+                else:
+                    # special cases for PEP 459
+                    sentinel = object()
+                    result = sentinel
+                    d = self._data.get('extensions')
+                    if d:
+                        if key == 'commands':
+                            result = d.get('python.commands', value)
+                        elif key == 'classifiers':
+                            d = d.get('python.details')
+                            if d:
+                                result = d.get(key, value)
+                        else:
+                            d = d.get('python.exports')
+                            if not d:
+                                d = self._data.get('python.exports')
+                            if d:
+                                result = d.get(key, value)
+                    if result is sentinel:
+                        result = value
+        elif key not in common:
+            result = object.__getattribute__(self, key)
+        elif self._legacy:
+            result = self._legacy.get(key)
+        else:
+            result = self._data.get(key)
+        return result
+
+    def _validate_value(self, key, value, scheme=None):
+        if key in self.SYNTAX_VALIDATORS:
+            pattern, exclusions = self.SYNTAX_VALIDATORS[key]
+            if (scheme or self.scheme) not in exclusions:
+                m = pattern.match(value)
+                if not m:
+                    raise MetadataInvalidError("'%s' is an invalid value for "
+                                               "the '%s' property" % (value,
+                                                                    key))
+
+    def __setattr__(self, key, value):
+        self._validate_value(key, value)
+        common = object.__getattribute__(self, 'common_keys')
+        mapped = object.__getattribute__(self, 'mapped_keys')
+        if key in mapped:
+            lk, _ = mapped[key]
+            if self._legacy:
+                if lk is None:
+                    raise NotImplementedError
+                self._legacy[lk] = value
+            elif key not in ('commands', 'exports', 'modules', 'namespaces',
+                             'classifiers'):
+                self._data[key] = value
+            else:
+                # special cases for PEP 459
+                d = self._data.setdefault('extensions', {})
+                if key == 'commands':
+                    d['python.commands'] = value
+                elif key == 'classifiers':
+                    d = d.setdefault('python.details', {})
+                    d[key] = value
+                else:
+                    d = d.setdefault('python.exports', {})
+                    d[key] = value
+        elif key not in common:
+            object.__setattr__(self, key, value)
+        else:
+            if key == 'keywords':
+                if isinstance(value, string_types):
+                    value = value.strip()
+                    if value:
+                        value = value.split()
+                    else:
+                        value = []
+            if self._legacy:
+                self._legacy[key] = value
+            else:
+                self._data[key] = value
+
+    @property
+    def name_and_version(self):
+        return _get_name_and_version(self.name, self.version, True)
+
+    @property
+    def provides(self):
+        if self._legacy:
+            result = self._legacy['Provides-Dist']
+        else:
+            result = self._data.setdefault('provides', [])
+        s = '%s (%s)' % (self.name, self.version)
+        if s not in result:
+            result.append(s)
+        return result
+
+    @provides.setter
+    def provides(self, value):
+        if self._legacy:
+            self._legacy['Provides-Dist'] = value
+        else:
+            self._data['provides'] = value
+
+    def get_requirements(self, reqts, extras=None, env=None):
+        """
+        Base method to get dependencies, given a set of extras
+        to satisfy and an optional environment context.
+        :param reqts: A list of sometimes-wanted dependencies,
+                      perhaps dependent on extras and environment.
+        :param extras: A list of optional components being requested.
+        :param env: An optional environment for marker evaluation.
+        """
+        if self._legacy:
+            result = reqts
+        else:
+            result = []
+            extras = get_extras(extras or [], self.extras)
+            for d in reqts:
+                if 'extra' not in d and 'environment' not in d:
+                    # unconditional
+                    include = True
+                else:
+                    if 'extra' not in d:
+                        # Not extra-dependent - only environment-dependent
+                        include = True
+                    else:
+                        include = d.get('extra') in extras
+                    if include:
+                        # Not excluded because of extras, check environment
+                        marker = d.get('environment')
+                        if marker:
+                            include = interpret(marker, env)
+                if include:
+                    result.extend(d['requires'])
+            for key in ('build', 'dev', 'test'):
+                e = ':%s:' % key
+                if e in extras:
+                    extras.remove(e)
+                    # A recursive call, but it should terminate since 'test'
+                    # has been removed from the extras
+                    reqts = self._data.get('%s_requires' % key, [])
+                    result.extend(self.get_requirements(reqts, extras=extras,
+                                                        env=env))
+        return result
+
+    @property
+    def dictionary(self):
+        if self._legacy:
+            return self._from_legacy()
+        return self._data
+
+    @property
+    def dependencies(self):
+        if self._legacy:
+            raise NotImplementedError
+        else:
+            return extract_by_key(self._data, self.DEPENDENCY_KEYS)
+
+    @dependencies.setter
+    def dependencies(self, value):
+        if self._legacy:
+            raise NotImplementedError
+        else:
+            self._data.update(value)
+
+    def _validate_mapping(self, mapping, scheme):
+        if mapping.get('metadata_version') != self.METADATA_VERSION:
+            raise MetadataUnrecognizedVersionError()
+        missing = []
+        for key, exclusions in self.MANDATORY_KEYS.items():
+            if key not in mapping:
+                if scheme not in exclusions:
+                    missing.append(key)
+        if missing:
+            msg = 'Missing metadata items: %s' % ', '.join(missing)
+            raise MetadataMissingError(msg)
+        for k, v in mapping.items():
+            self._validate_value(k, v, scheme)
+
+    def validate(self):
+        if self._legacy:
+            missing, warnings = self._legacy.check(True)
+            if missing or warnings:
+                logger.warning('Metadata: missing: %s, warnings: %s',
+                               missing, warnings)
+        else:
+            self._validate_mapping(self._data, self.scheme)
+
+    def todict(self):
+        if self._legacy:
+            return self._legacy.todict(True)
+        else:
+            result = extract_by_key(self._data, self.INDEX_KEYS)
+            return result
+
+    def _from_legacy(self):
+        assert self._legacy and not self._data
+        result = {
+            'metadata_version': self.METADATA_VERSION,
+            'generator': self.GENERATOR,
+        }
+        lmd = self._legacy.todict(True)     # skip missing ones
+        for k in ('name', 'version', 'license', 'summary', 'description',
+                  'classifier'):
+            if k in lmd:
+                if k == 'classifier':
+                    nk = 'classifiers'
+                else:
+                    nk = k
+                result[nk] = lmd[k]
+        kw = lmd.get('Keywords', [])
+        if kw == ['']:
+            kw = []
+        result['keywords'] = kw
+        keys = (('requires_dist', 'run_requires'),
+                ('setup_requires_dist', 'build_requires'))
+        for ok, nk in keys:
+            if ok in lmd and lmd[ok]:
+                result[nk] = [{'requires': lmd[ok]}]
+        result['provides'] = self.provides
+        author = {}
+        maintainer = {}
+        return result
+
+    LEGACY_MAPPING = {
+        'name': 'Name',
+        'version': 'Version',
+        'license': 'License',
+        'summary': 'Summary',
+        'description': 'Description',
+        'classifiers': 'Classifier',
+    }
+
+    def _to_legacy(self):
+        def process_entries(entries):
+            reqts = set()
+            for e in entries:
+                extra = e.get('extra')
+                env = e.get('environment')
+                rlist = e['requires']
+                for r in rlist:
+                    if not env and not extra:
+                        reqts.add(r)
+                    else:
+                        marker = ''
+                        if extra:
+                            marker = 'extra == "%s"' % extra
+                        if env:
+                            if marker:
+                                marker = '(%s) and %s' % (env, marker)
+                            else:
+                                marker = env
+                        reqts.add(';'.join((r, marker)))
+            return reqts
+
+        assert self._data and not self._legacy
+        result = LegacyMetadata()
+        nmd = self._data
+        for nk, ok in self.LEGACY_MAPPING.items():
+            if nk in nmd:
+                result[ok] = nmd[nk]
+        r1 = process_entries(self.run_requires + self.meta_requires)
+        r2 = process_entries(self.build_requires + self.dev_requires)
+        if self.extras:
+            result['Provides-Extra'] = sorted(self.extras)
+        result['Requires-Dist'] = sorted(r1)
+        result['Setup-Requires-Dist'] = sorted(r2)
+        # TODO: other fields such as contacts
+        return result
+
+    def write(self, path=None, fileobj=None, legacy=False, skip_unknown=True):
+        if [path, fileobj].count(None) != 1:
+            raise ValueError('Exactly one of path and fileobj is needed')
+        self.validate()
+        if legacy:
+            if self._legacy:
+                legacy_md = self._legacy
+            else:
+                legacy_md = self._to_legacy()
+            if path:
+                legacy_md.write(path, skip_unknown=skip_unknown)
+            else:
+                legacy_md.write_file(fileobj, skip_unknown=skip_unknown)
+        else:
+            if self._legacy:
+                d = self._from_legacy()
+            else:
+                d = self._data
+            if fileobj:
+                json.dump(d, fileobj, ensure_ascii=True, indent=2,
+                          sort_keys=True)
+            else:
+                with codecs.open(path, 'w', 'utf-8') as f:
+                    json.dump(d, f, ensure_ascii=True, indent=2,
+                              sort_keys=True)
+
+    def add_requirements(self, requirements):
+        if self._legacy:
+            self._legacy.add_requirements(requirements)
+        else:
+            run_requires = self._data.setdefault('run_requires', [])
+            always = None
+            for entry in run_requires:
+                if 'environment' not in entry and 'extra' not in entry:
+                    always = entry
+                    break
+            if always is None:
+                always = { 'requires': requirements }
+                run_requires.insert(0, always)
+            else:
+                rset = set(always['requires']) | set(requirements)
+                always['requires'] = sorted(rset)
+
+    def __repr__(self):
+        name = self.name or '(no name)'
+        version = self.version or 'no version'
+        return '<%s %s %s (%s)>' % (self.__class__.__name__,
+                                    self.metadata_version, name, version)