--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/env/lib/python3.7/site-packages/distlib/wheel.py	Sat May 02 07:14:21 2020 -0400
@@ -0,0 +1,1004 @@
+# -*- coding: utf-8 -*-
+#
+# Copyright (C) 2013-2017 Vinay Sajip.
+# Licensed to the Python Software Foundation under a contributor agreement.
+# See LICENSE.txt and CONTRIBUTORS.txt.
+#
+from __future__ import unicode_literals
+
+import base64
+import codecs
+import datetime
+import distutils.util
+from email import message_from_file
+import hashlib
+import imp
+import json
+import logging
+import os
+import posixpath
+import re
+import shutil
+import sys
+import tempfile
+import zipfile
+
+from . import __version__, DistlibException
+from .compat import sysconfig, ZipFile, fsdecode, text_type, filter
+from .database import InstalledDistribution
+from .metadata import Metadata, METADATA_FILENAME, WHEEL_METADATA_FILENAME
+from .util import (FileOperator, convert_path, CSVReader, CSVWriter, Cache,
+                   cached_property, get_cache_base, read_exports, tempdir)
+from .version import NormalizedVersion, UnsupportedVersionError
+
+logger = logging.getLogger(__name__)
+
+cache = None    # created when needed
+
+if hasattr(sys, 'pypy_version_info'):  # pragma: no cover
+    IMP_PREFIX = 'pp'
+elif sys.platform.startswith('java'):  # pragma: no cover
+    IMP_PREFIX = 'jy'
+elif sys.platform == 'cli':  # pragma: no cover
+    IMP_PREFIX = 'ip'
+else:
+    IMP_PREFIX = 'cp'
+
+VER_SUFFIX = sysconfig.get_config_var('py_version_nodot')
+if not VER_SUFFIX:   # pragma: no cover
+    VER_SUFFIX = '%s%s' % sys.version_info[:2]
+PYVER = 'py' + VER_SUFFIX
+IMPVER = IMP_PREFIX + VER_SUFFIX
+
+ARCH = distutils.util.get_platform().replace('-', '_').replace('.', '_')
+
+ABI = sysconfig.get_config_var('SOABI')
+if ABI and ABI.startswith('cpython-'):
+    ABI = ABI.replace('cpython-', 'cp')
+else:
+    def _derive_abi():
+        parts = ['cp', VER_SUFFIX]
+        if sysconfig.get_config_var('Py_DEBUG'):
+            parts.append('d')
+        if sysconfig.get_config_var('WITH_PYMALLOC'):
+            parts.append('m')
+        if sysconfig.get_config_var('Py_UNICODE_SIZE') == 4:
+            parts.append('u')
+        return ''.join(parts)
+    ABI = _derive_abi()
+    del _derive_abi
+
+FILENAME_RE = re.compile(r'''
+(?P<nm>[^-]+)
+-(?P<vn>\d+[^-]*)
+(-(?P<bn>\d+[^-]*))?
+-(?P<py>\w+\d+(\.\w+\d+)*)
+-(?P<bi>\w+)
+-(?P<ar>\w+(\.\w+)*)
+\.whl$
+''', re.IGNORECASE | re.VERBOSE)
+
+NAME_VERSION_RE = re.compile(r'''
+(?P<nm>[^-]+)
+-(?P<vn>\d+[^-]*)
+(-(?P<bn>\d+[^-]*))?$
+''', re.IGNORECASE | re.VERBOSE)
+
+SHEBANG_RE = re.compile(br'\s*#![^\r\n]*')
+SHEBANG_DETAIL_RE = re.compile(br'^(\s*#!("[^"]+"|\S+))\s+(.*)$')
+SHEBANG_PYTHON = b'#!python'
+SHEBANG_PYTHONW = b'#!pythonw'
+
+if os.sep == '/':
+    to_posix = lambda o: o
+else:
+    to_posix = lambda o: o.replace(os.sep, '/')
+
+
+class Mounter(object):
+    def __init__(self):
+        self.impure_wheels = {}
+        self.libs = {}
+
+    def add(self, pathname, extensions):
+        self.impure_wheels[pathname] = extensions
+        self.libs.update(extensions)
+
+    def remove(self, pathname):
+        extensions = self.impure_wheels.pop(pathname)
+        for k, v in extensions:
+            if k in self.libs:
+                del self.libs[k]
+
+    def find_module(self, fullname, path=None):
+        if fullname in self.libs:
+            result = self
+        else:
+            result = None
+        return result
+
+    def load_module(self, fullname):
+        if fullname in sys.modules:
+            result = sys.modules[fullname]
+        else:
+            if fullname not in self.libs:
+                raise ImportError('unable to find extension for %s' % fullname)
+            result = imp.load_dynamic(fullname, self.libs[fullname])
+            result.__loader__ = self
+            parts = fullname.rsplit('.', 1)
+            if len(parts) > 1:
+                result.__package__ = parts[0]
+        return result
+
+_hook = Mounter()
+
+
+class Wheel(object):
+    """
+    Class to build and install from Wheel files (PEP 427).
+    """
+
+    wheel_version = (1, 1)
+    hash_kind = 'sha256'
+
+    def __init__(self, filename=None, sign=False, verify=False):
+        """
+        Initialise an instance using a (valid) filename.
+        """
+        self.sign = sign
+        self.should_verify = verify
+        self.buildver = ''
+        self.pyver = [PYVER]
+        self.abi = ['none']
+        self.arch = ['any']
+        self.dirname = os.getcwd()
+        if filename is None:
+            self.name = 'dummy'
+            self.version = '0.1'
+            self._filename = self.filename
+        else:
+            m = NAME_VERSION_RE.match(filename)
+            if m:
+                info = m.groupdict('')
+                self.name = info['nm']
+                # Reinstate the local version separator
+                self.version = info['vn'].replace('_', '-')
+                self.buildver = info['bn']
+                self._filename = self.filename
+            else:
+                dirname, filename = os.path.split(filename)
+                m = FILENAME_RE.match(filename)
+                if not m:
+                    raise DistlibException('Invalid name or '
+                                           'filename: %r' % filename)
+                if dirname:
+                    self.dirname = os.path.abspath(dirname)
+                self._filename = filename
+                info = m.groupdict('')
+                self.name = info['nm']
+                self.version = info['vn']
+                self.buildver = info['bn']
+                self.pyver = info['py'].split('.')
+                self.abi = info['bi'].split('.')
+                self.arch = info['ar'].split('.')
+
+    @property
+    def filename(self):
+        """
+        Build and return a filename from the various components.
+        """
+        if self.buildver:
+            buildver = '-' + self.buildver
+        else:
+            buildver = ''
+        pyver = '.'.join(self.pyver)
+        abi = '.'.join(self.abi)
+        arch = '.'.join(self.arch)
+        # replace - with _ as a local version separator
+        version = self.version.replace('-', '_')
+        return '%s-%s%s-%s-%s-%s.whl' % (self.name, version, buildver,
+                                         pyver, abi, arch)
+
+    @property
+    def exists(self):
+        path = os.path.join(self.dirname, self.filename)
+        return os.path.isfile(path)
+
+    @property
+    def tags(self):
+        for pyver in self.pyver:
+            for abi in self.abi:
+                for arch in self.arch:
+                    yield pyver, abi, arch
+
+    @cached_property
+    def metadata(self):
+        pathname = os.path.join(self.dirname, self.filename)
+        name_ver = '%s-%s' % (self.name, self.version)
+        info_dir = '%s.dist-info' % name_ver
+        wrapper = codecs.getreader('utf-8')
+        with ZipFile(pathname, 'r') as zf:
+            wheel_metadata = self.get_wheel_metadata(zf)
+            wv = wheel_metadata['Wheel-Version'].split('.', 1)
+            file_version = tuple([int(i) for i in wv])
+            if file_version < (1, 1):
+                fns = [WHEEL_METADATA_FILENAME, METADATA_FILENAME, 'METADATA']
+            else:
+                fns = [WHEEL_METADATA_FILENAME, METADATA_FILENAME]
+            result = None
+            for fn in fns:
+                try:
+                    metadata_filename = posixpath.join(info_dir, fn)
+                    with zf.open(metadata_filename) as bf:
+                        wf = wrapper(bf)
+                        result = Metadata(fileobj=wf)
+                        if result:
+                            break
+                except KeyError:
+                    pass
+            if not result:
+                raise ValueError('Invalid wheel, because metadata is '
+                                 'missing: looked in %s' % ', '.join(fns))
+        return result
+
+    def get_wheel_metadata(self, zf):
+        name_ver = '%s-%s' % (self.name, self.version)
+        info_dir = '%s.dist-info' % name_ver
+        metadata_filename = posixpath.join(info_dir, 'WHEEL')
+        with zf.open(metadata_filename) as bf:
+            wf = codecs.getreader('utf-8')(bf)
+            message = message_from_file(wf)
+        return dict(message)
+
+    @cached_property
+    def info(self):
+        pathname = os.path.join(self.dirname, self.filename)
+        with ZipFile(pathname, 'r') as zf:
+            result = self.get_wheel_metadata(zf)
+        return result
+
+    def process_shebang(self, data):
+        m = SHEBANG_RE.match(data)
+        if m:
+            end = m.end()
+            shebang, data_after_shebang = data[:end], data[end:]
+            # Preserve any arguments after the interpreter
+            if b'pythonw' in shebang.lower():
+                shebang_python = SHEBANG_PYTHONW
+            else:
+                shebang_python = SHEBANG_PYTHON
+            m = SHEBANG_DETAIL_RE.match(shebang)
+            if m:
+                args = b' ' + m.groups()[-1]
+            else:
+                args = b''
+            shebang = shebang_python + args
+            data = shebang + data_after_shebang
+        else:
+            cr = data.find(b'\r')
+            lf = data.find(b'\n')
+            if cr < 0 or cr > lf:
+                term = b'\n'
+            else:
+                if data[cr:cr + 2] == b'\r\n':
+                    term = b'\r\n'
+                else:
+                    term = b'\r'
+            data = SHEBANG_PYTHON + term + data
+        return data
+
+    def get_hash(self, data, hash_kind=None):
+        if hash_kind is None:
+            hash_kind = self.hash_kind
+        try:
+            hasher = getattr(hashlib, hash_kind)
+        except AttributeError:
+            raise DistlibException('Unsupported hash algorithm: %r' % hash_kind)
+        result = hasher(data).digest()
+        result = base64.urlsafe_b64encode(result).rstrip(b'=').decode('ascii')
+        return hash_kind, result
+
+    def write_record(self, records, record_path, base):
+        records = list(records) # make a copy for sorting
+        p = to_posix(os.path.relpath(record_path, base))
+        records.append((p, '', ''))
+        records.sort()
+        with CSVWriter(record_path) as writer:
+            for row in records:
+                writer.writerow(row)
+
+    def write_records(self, info, libdir, archive_paths):
+        records = []
+        distinfo, info_dir = info
+        hasher = getattr(hashlib, self.hash_kind)
+        for ap, p in archive_paths:
+            with open(p, 'rb') as f:
+                data = f.read()
+            digest = '%s=%s' % self.get_hash(data)
+            size = os.path.getsize(p)
+            records.append((ap, digest, size))
+
+        p = os.path.join(distinfo, 'RECORD')
+        self.write_record(records, p, libdir)
+        ap = to_posix(os.path.join(info_dir, 'RECORD'))
+        archive_paths.append((ap, p))
+
+    def build_zip(self, pathname, archive_paths):
+        with ZipFile(pathname, 'w', zipfile.ZIP_DEFLATED) as zf:
+            for ap, p in archive_paths:
+                logger.debug('Wrote %s to %s in wheel', p, ap)
+                zf.write(p, ap)
+
+    def build(self, paths, tags=None, wheel_version=None):
+        """
+        Build a wheel from files in specified paths, and use any specified tags
+        when determining the name of the wheel.
+        """
+        if tags is None:
+            tags = {}
+
+        libkey = list(filter(lambda o: o in paths, ('purelib', 'platlib')))[0]
+        if libkey == 'platlib':
+            is_pure = 'false'
+            default_pyver = [IMPVER]
+            default_abi = [ABI]
+            default_arch = [ARCH]
+        else:
+            is_pure = 'true'
+            default_pyver = [PYVER]
+            default_abi = ['none']
+            default_arch = ['any']
+
+        self.pyver = tags.get('pyver', default_pyver)
+        self.abi = tags.get('abi', default_abi)
+        self.arch = tags.get('arch', default_arch)
+
+        libdir = paths[libkey]
+
+        name_ver = '%s-%s' % (self.name, self.version)
+        data_dir = '%s.data' % name_ver
+        info_dir = '%s.dist-info' % name_ver
+
+        archive_paths = []
+
+        # First, stuff which is not in site-packages
+        for key in ('data', 'headers', 'scripts'):
+            if key not in paths:
+                continue
+            path = paths[key]
+            if os.path.isdir(path):
+                for root, dirs, files in os.walk(path):
+                    for fn in files:
+                        p = fsdecode(os.path.join(root, fn))
+                        rp = os.path.relpath(p, path)
+                        ap = to_posix(os.path.join(data_dir, key, rp))
+                        archive_paths.append((ap, p))
+                        if key == 'scripts' and not p.endswith('.exe'):
+                            with open(p, 'rb') as f:
+                                data = f.read()
+                            data = self.process_shebang(data)
+                            with open(p, 'wb') as f:
+                                f.write(data)
+
+        # Now, stuff which is in site-packages, other than the
+        # distinfo stuff.
+        path = libdir
+        distinfo = None
+        for root, dirs, files in os.walk(path):
+            if root == path:
+                # At the top level only, save distinfo for later
+                # and skip it for now
+                for i, dn in enumerate(dirs):
+                    dn = fsdecode(dn)
+                    if dn.endswith('.dist-info'):
+                        distinfo = os.path.join(root, dn)
+                        del dirs[i]
+                        break
+                assert distinfo, '.dist-info directory expected, not found'
+
+            for fn in files:
+                # comment out next suite to leave .pyc files in
+                if fsdecode(fn).endswith(('.pyc', '.pyo')):
+                    continue
+                p = os.path.join(root, fn)
+                rp = to_posix(os.path.relpath(p, path))
+                archive_paths.append((rp, p))
+
+        # Now distinfo. Assumed to be flat, i.e. os.listdir is enough.
+        files = os.listdir(distinfo)
+        for fn in files:
+            if fn not in ('RECORD', 'INSTALLER', 'SHARED', 'WHEEL'):
+                p = fsdecode(os.path.join(distinfo, fn))
+                ap = to_posix(os.path.join(info_dir, fn))
+                archive_paths.append((ap, p))
+
+        wheel_metadata = [
+            'Wheel-Version: %d.%d' % (wheel_version or self.wheel_version),
+            'Generator: distlib %s' % __version__,
+            'Root-Is-Purelib: %s' % is_pure,
+        ]
+        for pyver, abi, arch in self.tags:
+            wheel_metadata.append('Tag: %s-%s-%s' % (pyver, abi, arch))
+        p = os.path.join(distinfo, 'WHEEL')
+        with open(p, 'w') as f:
+            f.write('\n'.join(wheel_metadata))
+        ap = to_posix(os.path.join(info_dir, 'WHEEL'))
+        archive_paths.append((ap, p))
+
+        # Now, at last, RECORD.
+        # Paths in here are archive paths - nothing else makes sense.
+        self.write_records((distinfo, info_dir), libdir, archive_paths)
+        # Now, ready to build the zip file
+        pathname = os.path.join(self.dirname, self.filename)
+        self.build_zip(pathname, archive_paths)
+        return pathname
+
+    def skip_entry(self, arcname):
+        """
+        Determine whether an archive entry should be skipped when verifying
+        or installing.
+        """
+        # The signature file won't be in RECORD,
+        # and we  don't currently don't do anything with it
+        # We also skip directories, as they won't be in RECORD
+        # either. See:
+        #
+        # https://github.com/pypa/wheel/issues/294
+        # https://github.com/pypa/wheel/issues/287
+        # https://github.com/pypa/wheel/pull/289
+        #
+        return arcname.endswith(('/', '/RECORD.jws'))
+
+    def install(self, paths, maker, **kwargs):
+        """
+        Install a wheel to the specified paths. If kwarg ``warner`` is
+        specified, it should be a callable, which will be called with two
+        tuples indicating the wheel version of this software and the wheel
+        version in the file, if there is a discrepancy in the versions.
+        This can be used to issue any warnings to raise any exceptions.
+        If kwarg ``lib_only`` is True, only the purelib/platlib files are
+        installed, and the headers, scripts, data and dist-info metadata are
+        not written. If kwarg ``bytecode_hashed_invalidation`` is True, written
+        bytecode will try to use file-hash based invalidation (PEP-552) on
+        supported interpreter versions (CPython 2.7+).
+
+        The return value is a :class:`InstalledDistribution` instance unless
+        ``options.lib_only`` is True, in which case the return value is ``None``.
+        """
+
+        dry_run = maker.dry_run
+        warner = kwargs.get('warner')
+        lib_only = kwargs.get('lib_only', False)
+        bc_hashed_invalidation = kwargs.get('bytecode_hashed_invalidation', False)
+
+        pathname = os.path.join(self.dirname, self.filename)
+        name_ver = '%s-%s' % (self.name, self.version)
+        data_dir = '%s.data' % name_ver
+        info_dir = '%s.dist-info' % name_ver
+
+        metadata_name = posixpath.join(info_dir, METADATA_FILENAME)
+        wheel_metadata_name = posixpath.join(info_dir, 'WHEEL')
+        record_name = posixpath.join(info_dir, 'RECORD')
+
+        wrapper = codecs.getreader('utf-8')
+
+        with ZipFile(pathname, 'r') as zf:
+            with zf.open(wheel_metadata_name) as bwf:
+                wf = wrapper(bwf)
+                message = message_from_file(wf)
+            wv = message['Wheel-Version'].split('.', 1)
+            file_version = tuple([int(i) for i in wv])
+            if (file_version != self.wheel_version) and warner:
+                warner(self.wheel_version, file_version)
+
+            if message['Root-Is-Purelib'] == 'true':
+                libdir = paths['purelib']
+            else:
+                libdir = paths['platlib']
+
+            records = {}
+            with zf.open(record_name) as bf:
+                with CSVReader(stream=bf) as reader:
+                    for row in reader:
+                        p = row[0]
+                        records[p] = row
+
+            data_pfx = posixpath.join(data_dir, '')
+            info_pfx = posixpath.join(info_dir, '')
+            script_pfx = posixpath.join(data_dir, 'scripts', '')
+
+            # make a new instance rather than a copy of maker's,
+            # as we mutate it
+            fileop = FileOperator(dry_run=dry_run)
+            fileop.record = True    # so we can rollback if needed
+
+            bc = not sys.dont_write_bytecode    # Double negatives. Lovely!
+
+            outfiles = []   # for RECORD writing
+
+            # for script copying/shebang processing
+            workdir = tempfile.mkdtemp()
+            # set target dir later
+            # we default add_launchers to False, as the
+            # Python Launcher should be used instead
+            maker.source_dir = workdir
+            maker.target_dir = None
+            try:
+                for zinfo in zf.infolist():
+                    arcname = zinfo.filename
+                    if isinstance(arcname, text_type):
+                        u_arcname = arcname
+                    else:
+                        u_arcname = arcname.decode('utf-8')
+                    if self.skip_entry(u_arcname):
+                        continue
+                    row = records[u_arcname]
+                    if row[2] and str(zinfo.file_size) != row[2]:
+                        raise DistlibException('size mismatch for '
+                                               '%s' % u_arcname)
+                    if row[1]:
+                        kind, value = row[1].split('=', 1)
+                        with zf.open(arcname) as bf:
+                            data = bf.read()
+                        _, digest = self.get_hash(data, kind)
+                        if digest != value:
+                            raise DistlibException('digest mismatch for '
+                                                   '%s' % arcname)
+
+                    if lib_only and u_arcname.startswith((info_pfx, data_pfx)):
+                        logger.debug('lib_only: skipping %s', u_arcname)
+                        continue
+                    is_script = (u_arcname.startswith(script_pfx)
+                                 and not u_arcname.endswith('.exe'))
+
+                    if u_arcname.startswith(data_pfx):
+                        _, where, rp = u_arcname.split('/', 2)
+                        outfile = os.path.join(paths[where], convert_path(rp))
+                    else:
+                        # meant for site-packages.
+                        if u_arcname in (wheel_metadata_name, record_name):
+                            continue
+                        outfile = os.path.join(libdir, convert_path(u_arcname))
+                    if not is_script:
+                        with zf.open(arcname) as bf:
+                            fileop.copy_stream(bf, outfile)
+                        outfiles.append(outfile)
+                        # Double check the digest of the written file
+                        if not dry_run and row[1]:
+                            with open(outfile, 'rb') as bf:
+                                data = bf.read()
+                                _, newdigest = self.get_hash(data, kind)
+                                if newdigest != digest:
+                                    raise DistlibException('digest mismatch '
+                                                           'on write for '
+                                                           '%s' % outfile)
+                        if bc and outfile.endswith('.py'):
+                            try:
+                                pyc = fileop.byte_compile(outfile,
+                                                          hashed_invalidation=bc_hashed_invalidation)
+                                outfiles.append(pyc)
+                            except Exception:
+                                # Don't give up if byte-compilation fails,
+                                # but log it and perhaps warn the user
+                                logger.warning('Byte-compilation failed',
+                                               exc_info=True)
+                    else:
+                        fn = os.path.basename(convert_path(arcname))
+                        workname = os.path.join(workdir, fn)
+                        with zf.open(arcname) as bf:
+                            fileop.copy_stream(bf, workname)
+
+                        dn, fn = os.path.split(outfile)
+                        maker.target_dir = dn
+                        filenames = maker.make(fn)
+                        fileop.set_executable_mode(filenames)
+                        outfiles.extend(filenames)
+
+                if lib_only:
+                    logger.debug('lib_only: returning None')
+                    dist = None
+                else:
+                    # Generate scripts
+
+                    # Try to get pydist.json so we can see if there are
+                    # any commands to generate. If this fails (e.g. because
+                    # of a legacy wheel), log a warning but don't give up.
+                    commands = None
+                    file_version = self.info['Wheel-Version']
+                    if file_version == '1.0':
+                        # Use legacy info
+                        ep = posixpath.join(info_dir, 'entry_points.txt')
+                        try:
+                            with zf.open(ep) as bwf:
+                                epdata = read_exports(bwf)
+                            commands = {}
+                            for key in ('console', 'gui'):
+                                k = '%s_scripts' % key
+                                if k in epdata:
+                                    commands['wrap_%s' % key] = d = {}
+                                    for v in epdata[k].values():
+                                        s = '%s:%s' % (v.prefix, v.suffix)
+                                        if v.flags:
+                                            s += ' %s' % v.flags
+                                        d[v.name] = s
+                        except Exception:
+                            logger.warning('Unable to read legacy script '
+                                           'metadata, so cannot generate '
+                                           'scripts')
+                    else:
+                        try:
+                            with zf.open(metadata_name) as bwf:
+                                wf = wrapper(bwf)
+                                commands = json.load(wf).get('extensions')
+                                if commands:
+                                    commands = commands.get('python.commands')
+                        except Exception:
+                            logger.warning('Unable to read JSON metadata, so '
+                                           'cannot generate scripts')
+                    if commands:
+                        console_scripts = commands.get('wrap_console', {})
+                        gui_scripts = commands.get('wrap_gui', {})
+                        if console_scripts or gui_scripts:
+                            script_dir = paths.get('scripts', '')
+                            if not os.path.isdir(script_dir):
+                                raise ValueError('Valid script path not '
+                                                 'specified')
+                            maker.target_dir = script_dir
+                            for k, v in console_scripts.items():
+                                script = '%s = %s' % (k, v)
+                                filenames = maker.make(script)
+                                fileop.set_executable_mode(filenames)
+
+                            if gui_scripts:
+                                options = {'gui': True }
+                                for k, v in gui_scripts.items():
+                                    script = '%s = %s' % (k, v)
+                                    filenames = maker.make(script, options)
+                                    fileop.set_executable_mode(filenames)
+
+                    p = os.path.join(libdir, info_dir)
+                    dist = InstalledDistribution(p)
+
+                    # Write SHARED
+                    paths = dict(paths)     # don't change passed in dict
+                    del paths['purelib']
+                    del paths['platlib']
+                    paths['lib'] = libdir
+                    p = dist.write_shared_locations(paths, dry_run)
+                    if p:
+                        outfiles.append(p)
+
+                    # Write RECORD
+                    dist.write_installed_files(outfiles, paths['prefix'],
+                                               dry_run)
+                return dist
+            except Exception:  # pragma: no cover
+                logger.exception('installation failed.')
+                fileop.rollback()
+                raise
+            finally:
+                shutil.rmtree(workdir)
+
+    def _get_dylib_cache(self):
+        global cache
+        if cache is None:
+            # Use native string to avoid issues on 2.x: see Python #20140.
+            base = os.path.join(get_cache_base(), str('dylib-cache'),
+                                '%s.%s' % sys.version_info[:2])
+            cache = Cache(base)
+        return cache
+
+    def _get_extensions(self):
+        pathname = os.path.join(self.dirname, self.filename)
+        name_ver = '%s-%s' % (self.name, self.version)
+        info_dir = '%s.dist-info' % name_ver
+        arcname = posixpath.join(info_dir, 'EXTENSIONS')
+        wrapper = codecs.getreader('utf-8')
+        result = []
+        with ZipFile(pathname, 'r') as zf:
+            try:
+                with zf.open(arcname) as bf:
+                    wf = wrapper(bf)
+                    extensions = json.load(wf)
+                    cache = self._get_dylib_cache()
+                    prefix = cache.prefix_to_dir(pathname)
+                    cache_base = os.path.join(cache.base, prefix)
+                    if not os.path.isdir(cache_base):
+                        os.makedirs(cache_base)
+                    for name, relpath in extensions.items():
+                        dest = os.path.join(cache_base, convert_path(relpath))
+                        if not os.path.exists(dest):
+                            extract = True
+                        else:
+                            file_time = os.stat(dest).st_mtime
+                            file_time = datetime.datetime.fromtimestamp(file_time)
+                            info = zf.getinfo(relpath)
+                            wheel_time = datetime.datetime(*info.date_time)
+                            extract = wheel_time > file_time
+                        if extract:
+                            zf.extract(relpath, cache_base)
+                        result.append((name, dest))
+            except KeyError:
+                pass
+        return result
+
+    def is_compatible(self):
+        """
+        Determine if a wheel is compatible with the running system.
+        """
+        return is_compatible(self)
+
+    def is_mountable(self):
+        """
+        Determine if a wheel is asserted as mountable by its metadata.
+        """
+        return True # for now - metadata details TBD
+
+    def mount(self, append=False):
+        pathname = os.path.abspath(os.path.join(self.dirname, self.filename))
+        if not self.is_compatible():
+            msg = 'Wheel %s not compatible with this Python.' % pathname
+            raise DistlibException(msg)
+        if not self.is_mountable():
+            msg = 'Wheel %s is marked as not mountable.' % pathname
+            raise DistlibException(msg)
+        if pathname in sys.path:
+            logger.debug('%s already in path', pathname)
+        else:
+            if append:
+                sys.path.append(pathname)
+            else:
+                sys.path.insert(0, pathname)
+            extensions = self._get_extensions()
+            if extensions:
+                if _hook not in sys.meta_path:
+                    sys.meta_path.append(_hook)
+                _hook.add(pathname, extensions)
+
+    def unmount(self):
+        pathname = os.path.abspath(os.path.join(self.dirname, self.filename))
+        if pathname not in sys.path:
+            logger.debug('%s not in path', pathname)
+        else:
+            sys.path.remove(pathname)
+            if pathname in _hook.impure_wheels:
+                _hook.remove(pathname)
+            if not _hook.impure_wheels:
+                if _hook in sys.meta_path:
+                    sys.meta_path.remove(_hook)
+
+    def verify(self):
+        pathname = os.path.join(self.dirname, self.filename)
+        name_ver = '%s-%s' % (self.name, self.version)
+        data_dir = '%s.data' % name_ver
+        info_dir = '%s.dist-info' % name_ver
+
+        metadata_name = posixpath.join(info_dir, METADATA_FILENAME)
+        wheel_metadata_name = posixpath.join(info_dir, 'WHEEL')
+        record_name = posixpath.join(info_dir, 'RECORD')
+
+        wrapper = codecs.getreader('utf-8')
+
+        with ZipFile(pathname, 'r') as zf:
+            with zf.open(wheel_metadata_name) as bwf:
+                wf = wrapper(bwf)
+                message = message_from_file(wf)
+            wv = message['Wheel-Version'].split('.', 1)
+            file_version = tuple([int(i) for i in wv])
+            # TODO version verification
+
+            records = {}
+            with zf.open(record_name) as bf:
+                with CSVReader(stream=bf) as reader:
+                    for row in reader:
+                        p = row[0]
+                        records[p] = row
+
+            for zinfo in zf.infolist():
+                arcname = zinfo.filename
+                if isinstance(arcname, text_type):
+                    u_arcname = arcname
+                else:
+                    u_arcname = arcname.decode('utf-8')
+                # See issue #115: some wheels have .. in their entries, but
+                # in the filename ... e.g. __main__..py ! So the check is
+                # updated to look for .. in the directory portions
+                p = u_arcname.split('/')
+                if '..' in p:
+                    raise DistlibException('invalid entry in '
+                                           'wheel: %r' % u_arcname)
+
+                if self.skip_entry(u_arcname):
+                    continue
+                row = records[u_arcname]
+                if row[2] and str(zinfo.file_size) != row[2]:
+                    raise DistlibException('size mismatch for '
+                                           '%s' % u_arcname)
+                if row[1]:
+                    kind, value = row[1].split('=', 1)
+                    with zf.open(arcname) as bf:
+                        data = bf.read()
+                    _, digest = self.get_hash(data, kind)
+                    if digest != value:
+                        raise DistlibException('digest mismatch for '
+                                               '%s' % arcname)
+
+    def update(self, modifier, dest_dir=None, **kwargs):
+        """
+        Update the contents of a wheel in a generic way. The modifier should
+        be a callable which expects a dictionary argument: its keys are
+        archive-entry paths, and its values are absolute filesystem paths
+        where the contents the corresponding archive entries can be found. The
+        modifier is free to change the contents of the files pointed to, add
+        new entries and remove entries, before returning. This method will
+        extract the entire contents of the wheel to a temporary location, call
+        the modifier, and then use the passed (and possibly updated)
+        dictionary to write a new wheel. If ``dest_dir`` is specified, the new
+        wheel is written there -- otherwise, the original wheel is overwritten.
+
+        The modifier should return True if it updated the wheel, else False.
+        This method returns the same value the modifier returns.
+        """
+
+        def get_version(path_map, info_dir):
+            version = path = None
+            key = '%s/%s' % (info_dir, METADATA_FILENAME)
+            if key not in path_map:
+                key = '%s/PKG-INFO' % info_dir
+            if key in path_map:
+                path = path_map[key]
+                version = Metadata(path=path).version
+            return version, path
+
+        def update_version(version, path):
+            updated = None
+            try:
+                v = NormalizedVersion(version)
+                i = version.find('-')
+                if i < 0:
+                    updated = '%s+1' % version
+                else:
+                    parts = [int(s) for s in version[i + 1:].split('.')]
+                    parts[-1] += 1
+                    updated = '%s+%s' % (version[:i],
+                                         '.'.join(str(i) for i in parts))
+            except UnsupportedVersionError:
+                logger.debug('Cannot update non-compliant (PEP-440) '
+                             'version %r', version)
+            if updated:
+                md = Metadata(path=path)
+                md.version = updated
+                legacy = not path.endswith(METADATA_FILENAME)
+                md.write(path=path, legacy=legacy)
+                logger.debug('Version updated from %r to %r', version,
+                             updated)
+
+        pathname = os.path.join(self.dirname, self.filename)
+        name_ver = '%s-%s' % (self.name, self.version)
+        info_dir = '%s.dist-info' % name_ver
+        record_name = posixpath.join(info_dir, 'RECORD')
+        with tempdir() as workdir:
+            with ZipFile(pathname, 'r') as zf:
+                path_map = {}
+                for zinfo in zf.infolist():
+                    arcname = zinfo.filename
+                    if isinstance(arcname, text_type):
+                        u_arcname = arcname
+                    else:
+                        u_arcname = arcname.decode('utf-8')
+                    if u_arcname == record_name:
+                        continue
+                    if '..' in u_arcname:
+                        raise DistlibException('invalid entry in '
+                                               'wheel: %r' % u_arcname)
+                    zf.extract(zinfo, workdir)
+                    path = os.path.join(workdir, convert_path(u_arcname))
+                    path_map[u_arcname] = path
+
+            # Remember the version.
+            original_version, _ = get_version(path_map, info_dir)
+            # Files extracted. Call the modifier.
+            modified = modifier(path_map, **kwargs)
+            if modified:
+                # Something changed - need to build a new wheel.
+                current_version, path = get_version(path_map, info_dir)
+                if current_version and (current_version == original_version):
+                    # Add or update local version to signify changes.
+                    update_version(current_version, path)
+                # Decide where the new wheel goes.
+                if dest_dir is None:
+                    fd, newpath = tempfile.mkstemp(suffix='.whl',
+                                                   prefix='wheel-update-',
+                                                   dir=workdir)
+                    os.close(fd)
+                else:
+                    if not os.path.isdir(dest_dir):
+                        raise DistlibException('Not a directory: %r' % dest_dir)
+                    newpath = os.path.join(dest_dir, self.filename)
+                archive_paths = list(path_map.items())
+                distinfo = os.path.join(workdir, info_dir)
+                info = distinfo, info_dir
+                self.write_records(info, workdir, archive_paths)
+                self.build_zip(newpath, archive_paths)
+                if dest_dir is None:
+                    shutil.copyfile(newpath, pathname)
+        return modified
+
+def compatible_tags():
+    """
+    Return (pyver, abi, arch) tuples compatible with this Python.
+    """
+    versions = [VER_SUFFIX]
+    major = VER_SUFFIX[0]
+    for minor in range(sys.version_info[1] - 1, - 1, -1):
+        versions.append(''.join([major, str(minor)]))
+
+    abis = []
+    for suffix, _, _ in imp.get_suffixes():
+        if suffix.startswith('.abi'):
+            abis.append(suffix.split('.', 2)[1])
+    abis.sort()
+    if ABI != 'none':
+        abis.insert(0, ABI)
+    abis.append('none')
+    result = []
+
+    arches = [ARCH]
+    if sys.platform == 'darwin':
+        m = re.match(r'(\w+)_(\d+)_(\d+)_(\w+)$', ARCH)
+        if m:
+            name, major, minor, arch = m.groups()
+            minor = int(minor)
+            matches = [arch]
+            if arch in ('i386', 'ppc'):
+                matches.append('fat')
+            if arch in ('i386', 'ppc', 'x86_64'):
+                matches.append('fat3')
+            if arch in ('ppc64', 'x86_64'):
+                matches.append('fat64')
+            if arch in ('i386', 'x86_64'):
+                matches.append('intel')
+            if arch in ('i386', 'x86_64', 'intel', 'ppc', 'ppc64'):
+                matches.append('universal')
+            while minor >= 0:
+                for match in matches:
+                    s = '%s_%s_%s_%s' % (name, major, minor, match)
+                    if s != ARCH:   # already there
+                        arches.append(s)
+                minor -= 1
+
+    # Most specific - our Python version, ABI and arch
+    for abi in abis:
+        for arch in arches:
+            result.append((''.join((IMP_PREFIX, versions[0])), abi, arch))
+
+    # where no ABI / arch dependency, but IMP_PREFIX dependency
+    for i, version in enumerate(versions):
+        result.append((''.join((IMP_PREFIX, version)), 'none', 'any'))
+        if i == 0:
+            result.append((''.join((IMP_PREFIX, version[0])), 'none', 'any'))
+
+    # no IMP_PREFIX, ABI or arch dependency
+    for i, version in enumerate(versions):
+        result.append((''.join(('py', version)), 'none', 'any'))
+        if i == 0:
+            result.append((''.join(('py', version[0])), 'none', 'any'))
+    return set(result)
+
+
+COMPATIBLE_TAGS = compatible_tags()
+
+del compatible_tags
+
+
+def is_compatible(wheel, tags=None):
+    if not isinstance(wheel, Wheel):
+        wheel = Wheel(wheel)    # assume it's a filename
+    result = False
+    if tags is None:
+        tags = COMPATIBLE_TAGS
+    for ver, abi, arch in tags:
+        if ver in wheel.pyver and abi in wheel.abi and arch in wheel.arch:
+            result = True
+            break
+    return result