1 files changed, 737 insertions, 0 deletions
diff --git a/venv/lib/python3.7/site-packages/pip-10.0.1-py3.7.egg/pip/_vendor/requests/sessions.py b/venv/lib/python3.7/site-packages/pip-10.0.1-py3.7.egg/pip/_vendor/requests/sessions.py
new file mode 100644
index 0000000..d8eafa8
--- /dev/null
+++ b/venv/lib/python3.7/site-packages/pip-10.0.1-py3.7.egg/pip/_vendor/requests/sessions.py
@@ -0,0 +1,737 @@
+# -*- coding: utf-8 -*-
+"""
+requests.session
+~~~~~~~~~~~~~~~~
+This module provides a Session object to manage and persist settings across
+requests (cookies, auth, proxies).
+"""
+import os
+import platform
+import time
+from collections import Mapping
+from datetime import timedelta
+from .auth import _basic_auth_str
+from .compat import cookielib, is_py3, OrderedDict, urljoin, urlparse
+from .cookies import (
+    cookiejar_from_dict, extract_cookies_to_jar, RequestsCookieJar, merge_cookies)
+from .models import Request, PreparedRequest, DEFAULT_REDIRECT_LIMIT
+from .hooks import default_hooks, dispatch_hook
+from ._internal_utils import to_native_string
+from .utils import to_key_val_list, default_headers
+from .exceptions import (
+    TooManyRedirects, InvalidSchema, ChunkedEncodingError, ContentDecodingError)
+from .structures import CaseInsensitiveDict
+from .adapters import HTTPAdapter
+from .utils import (
+    requote_uri, get_environ_proxies, get_netrc_auth, should_bypass_proxies,
+    get_auth_from_url, rewind_body
+)
+from .status_codes import codes
+# formerly defined here, reexposed here for backward compatibility
+from .models import REDIRECT_STATI
+# Preferred clock, based on which one is more accurate on a given system.
+if platform.system() == 'Windows':
+    try:  # Python 3.3+
+        preferred_clock = time.perf_counter
+    except AttributeError:  # Earlier than Python 3.
+        preferred_clock = time.clock
+else:
+    preferred_clock = time.time
+def merge_setting(request_setting, session_setting, dict_class=OrderedDict):
+    """Determines appropriate setting for a given request, taking into account
+    the explicit setting on that request, and the setting in the session. If a
+    setting is a dictionary, they will be merged together using `dict_class`
+    """
+    if session_setting is None:
+        return request_setting
+    if request_setting is None:
+        return session_setting
+    # Bypass if not a dictionary (e.g. verify)
+    if not (
+            isinstance(session_setting, Mapping) and
+            isinstance(request_setting, Mapping)
+    ):
+        return request_setting
+    merged_setting = dict_class(to_key_val_list(session_setting))
+    merged_setting.update(to_key_val_list(request_setting))
+    # Remove keys that are set to None. Extract keys first to avoid altering
+    # the dictionary during iteration.
+    none_keys = [k for (k, v) in merged_setting.items() if v is None]
+    for key in none_keys:
+        del merged_setting[key]
+    return merged_setting
+def merge_hooks(request_hooks, session_hooks, dict_class=OrderedDict):
+    """Properly merges both requests and session hooks.
+    This is necessary because when request_hooks == {'response': []}, the
+    merge breaks Session hooks entirely.
+    """
+    if session_hooks is None or session_hooks.get('response') == []:
+        return request_hooks
+    if request_hooks is None or request_hooks.get('response') == []:
+        return session_hooks
+    return merge_setting(request_hooks, session_hooks, dict_class)
+class SessionRedirectMixin(object):
+    def get_redirect_target(self, resp):
+        """Receives a Response. Returns a redirect URI or ``None``"""
+        # Due to the nature of how requests processes redirects this method will
+        # be called at least once upon the original response and at least twice
+        # on each subsequent redirect response (if any).
+        # If a custom mixin is used to handle this logic, it may be advantageous
+        # to cache the redirect location onto the response object as a private
+        # attribute.
+        if resp.is_redirect:
+            location = resp.headers['location']
+            # Currently the underlying http module on py3 decode headers
+            # in latin1, but empirical evidence suggests that latin1 is very
+            # rarely used with non-ASCII characters in HTTP headers.
+            # It is more likely to get UTF8 header rather than latin1.
+            # This causes incorrect handling of UTF8 encoded location headers.
+            # To solve this, we re-encode the location in latin1.
+            if is_py3:
+                location = location.encode('latin1')
+            return to_native_string(location, 'utf8')
+        return None
+    def resolve_redirects(self, resp, req, stream=False, timeout=None,
+                          verify=True, cert=None, proxies=None, yield_requests=False, **adapter_kwargs):
+        """Receives a Response. Returns a generator of Responses or Requests."""
+        hist = []  # keep track of history
+        url = self.get_redirect_target(resp)
+        while url:
+            prepared_request = req.copy()
+            # Update history and keep track of redirects.
+            # resp.history must ignore the original request in this loop
+            hist.append(resp)
+            resp.history = hist[1:]
+            try:
+                resp.content  # Consume socket so it can be released
+            except (ChunkedEncodingError, ContentDecodingError, RuntimeError):
+                resp.raw.read(decode_content=False)
+            if len(resp.history) >= self.max_redirects:
+                raise TooManyRedirects('Exceeded %s redirects.' % self.max_redirects, response=resp)
+            # Release the connection back into the pool.
+            resp.close()
+            # Handle redirection without scheme (see: RFC 1808 Section 4)
+            if url.startswith('//'):
+                parsed_rurl = urlparse(resp.url)
+                url = '%s:%s' % (to_native_string(parsed_rurl.scheme), url)
+            # The scheme should be lower case...
+            parsed = urlparse(url)
+            url = parsed.geturl()
+            # Facilitate relative 'location' headers, as allowed by RFC 7231.
+            # (e.g. '/path/to/resource' instead of 'http://domain.tld/path/to/resource')
+            # Compliant with RFC3986, we percent encode the url.
+            if not parsed.netloc:
+                url = urljoin(resp.url, requote_uri(url))
+            else:
+                url = requote_uri(url)
+            prepared_request.url = to_native_string(url)
+            self.rebuild_method(prepared_request, resp)
+            # https://github.com/requests/requests/issues/1084
+            if resp.status_code not in (codes.temporary_redirect, codes.permanent_redirect):
+                # https://github.com/requests/requests/issues/3490
+                purged_headers = ('Content-Length', 'Content-Type', 'Transfer-Encoding')
+                for header in purged_headers:
+                    prepared_request.headers.pop(header, None)
+                prepared_request.body = None
+            headers = prepared_request.headers
+            try:
+                del headers['Cookie']
+            except KeyError:
+                pass
+            # Extract any cookies sent on the response to the cookiejar
+            # in the new request. Because we've mutated our copied prepared
+            # request, use the old one that we haven't yet touched.
+            extract_cookies_to_jar(prepared_request._cookies, req, resp.raw)
+            merge_cookies(prepared_request._cookies, self.cookies)
+            prepared_request.prepare_cookies(prepared_request._cookies)
+            # Rebuild auth and proxy information.
+            proxies = self.rebuild_proxies(prepared_request, proxies)
+            self.rebuild_auth(prepared_request, resp)
+            # A failed tell() sets `_body_position` to `object()`. This non-None
+            # value ensures `rewindable` will be True, allowing us to raise an
+            # UnrewindableBodyError, instead of hanging the connection.
+            rewindable = (
+                prepared_request._body_position is not None and
+                ('Content-Length' in headers or 'Transfer-Encoding' in headers)
+            )
+            # Attempt to rewind consumed file-like object.
+            if rewindable:
+                rewind_body(prepared_request)
+            # Override the original request.
+            req = prepared_request
+            if yield_requests:
+                yield req
+            else:
+                resp = self.send(
+                    req,
+                    stream=stream,
+                    timeout=timeout,
+                    verify=verify,
+                    cert=cert,
+                    proxies=proxies,
+                    allow_redirects=False,
+                    **adapter_kwargs
+                )
+                extract_cookies_to_jar(self.cookies, prepared_request, resp.raw)
+                # extract redirect url, if any, for the next loop
+                url = self.get_redirect_target(resp)
+                yield resp
+    def rebuild_auth(self, prepared_request, response):
+        """When being redirected we may want to strip authentication from the
+        request to avoid leaking credentials. This method intelligently removes
+        and reapplies authentication where possible to avoid credential loss.
+        """
+        headers = prepared_request.headers
+        url = prepared_request.url
+        if 'Authorization' in headers:
+            # If we get redirected to a new host, we should strip out any
+            # authentication headers.
+            original_parsed = urlparse(response.request.url)
+            redirect_parsed = urlparse(url)
+            if (original_parsed.hostname != redirect_parsed.hostname):
+                del headers['Authorization']
+        # .netrc might have more auth for us on our new host.
+        new_auth = get_netrc_auth(url) if self.trust_env else None
+        if new_auth is not None:
+            prepared_request.prepare_auth(new_auth)
+        return
+    def rebuild_proxies(self, prepared_request, proxies):
+        """This method re-evaluates the proxy configuration by considering the
+        environment variables. If we are redirected to a URL covered by
+        NO_PROXY, we strip the proxy configuration. Otherwise, we set missing
+        proxy keys for this URL (in case they were stripped by a previous
+        redirect).
+        This method also replaces the Proxy-Authorization header where
+        necessary.
+        :rtype: dict
+        """
+        proxies = proxies if proxies is not None else {}
+        headers = prepared_request.headers
+        url = prepared_request.url
+        scheme = urlparse(url).scheme
+        new_proxies = proxies.copy()
+        no_proxy = proxies.get('no_proxy')
+        bypass_proxy = should_bypass_proxies(url, no_proxy=no_proxy)
+        if self.trust_env and not bypass_proxy:
+            environ_proxies = get_environ_proxies(url, no_proxy=no_proxy)
+            proxy = environ_proxies.get(scheme, environ_proxies.get('all'))
+            if proxy:
+                new_proxies.setdefault(scheme, proxy)
+        if 'Proxy-Authorization' in headers:
+            del headers['Proxy-Authorization']
+        try:
+            username, password = get_auth_from_url(new_proxies[scheme])
+        except KeyError:
+            username, password = None, None
+        if username and password:
+            headers['Proxy-Authorization'] = _basic_auth_str(username, password)
+        return new_proxies
+    def rebuild_method(self, prepared_request, response):
+        """When being redirected we may want to change the method of the request
+        based on certain specs or browser behavior.
+        """
+        method = prepared_request.method
+        # http://tools.ietf.org/html/rfc7231#section-6.4.4
+        if response.status_code == codes.see_other and method != 'HEAD':
+            method = 'GET'
+        # Do what the browsers do, despite standards...
+        # First, turn 302s into GETs.
+        if response.status_code == codes.found and method != 'HEAD':
+            method = 'GET'
+        # Second, if a POST is responded to with a 301, turn it into a GET.
+        # This bizarre behaviour is explained in Issue 1704.
+        if response.status_code == codes.moved and method == 'POST':
+            method = 'GET'
+        prepared_request.method = method
+class Session(SessionRedirectMixin):
+    """A Requests session.
+    Provides cookie persistence, connection-pooling, and configuration.
+    Basic Usage::
+      >>> import requests
+      >>> s = requests.Session()
+      >>> s.get('http://httpbin.org/get')
+      <Response [200]>
+    Or as a context manager::
+      >>> with requests.Session() as s:
+      >>>     s.get('http://httpbin.org/get')
+      <Response [200]>
+    """
+    __attrs__ = [
+        'headers', 'cookies', 'auth', 'proxies', 'hooks', 'params', 'verify',
+        'cert', 'prefetch', 'adapters', 'stream', 'trust_env',
+        'max_redirects',
+    ]
+    def __init__(self):
+        #: A case-insensitive dictionary of headers to be sent on each
+        #: :class:`Request <Request>` sent from this
+        #: :class:`Session <Session>`.
+        self.headers = default_headers()
+        #: Default Authentication tuple or object to attach to
+        #: :class:`Request <Request>`.
+        self.auth = None
+        #: Dictionary mapping protocol or protocol and host to the URL of the proxy
+        #: (e.g. {'http': 'foo.bar:3128', 'http://host.name': 'foo.bar:4012'}) to
+        #: be used on each :class:`Request <Request>`.
+        self.proxies = {}
+        #: Event-handling hooks.
+        self.hooks = default_hooks()
+        #: Dictionary of querystring data to attach to each
+        #: :class:`Request <Request>`. The dictionary values may be lists for
+        #: representing multivalued query parameters.
+        self.params = {}
+        #: Stream response content default.
+        self.stream = False
+        #: SSL Verification default.
+        self.verify = True
+        #: SSL client certificate default, if String, path to ssl client
+        #: cert file (.pem). If Tuple, ('cert', 'key') pair.
+        self.cert = None
+        #: Maximum number of redirects allowed. If the request exceeds this
+        #: limit, a :class:`TooManyRedirects` exception is raised.
+        #: This defaults to requests.models.DEFAULT_REDIRECT_LIMIT, which is
+        #: 30.
+        self.max_redirects = DEFAULT_REDIRECT_LIMIT
+        #: Trust environment settings for proxy configuration, default
+        #: authentication and similar.
+        self.trust_env = True
+        #: A CookieJar containing all currently outstanding cookies set on this
+        #: session. By default it is a
+        #: :class:`RequestsCookieJar <requests.cookies.RequestsCookieJar>`, but
+        #: may be any other ``cookielib.CookieJar`` compatible object.
+        self.cookies = cookiejar_from_dict({})
+        # Default connection adapters.
+        self.adapters = OrderedDict()
+        self.mount('https://', HTTPAdapter())
+        self.mount('http://', HTTPAdapter())
+    def __enter__(self):
+        return self
+    def __exit__(self, *args):
+        self.close()
+    def prepare_request(self, request):
+        """Constructs a :class:`PreparedRequest <PreparedRequest>` for
+        transmission and returns it. The :class:`PreparedRequest` has settings
+        merged from the :class:`Request <Request>` instance and those of the
+        :class:`Session`.
+        :param request: :class:`Request` instance to prepare with this
+            session's settings.
+        :rtype: requests.PreparedRequest
+        """
+        cookies = request.cookies or {}
+        # Bootstrap CookieJar.
+        if not isinstance(cookies, cookielib.CookieJar):
+            cookies = cookiejar_from_dict(cookies)
+        # Merge with session cookies
+        merged_cookies = merge_cookies(
+            merge_cookies(RequestsCookieJar(), self.cookies), cookies)
+        # Set environment's basic authentication if not explicitly set.
+        auth = request.auth
+        if self.trust_env and not auth and not self.auth:
+            auth = get_netrc_auth(request.url)
+        p = PreparedRequest()
+        p.prepare(
+            method=request.method.upper(),
+            url=request.url,
+            files=request.files,
+            data=request.data,
+            json=request.json,
+            headers=merge_setting(request.headers, self.headers, dict_class=CaseInsensitiveDict),
+            params=merge_setting(request.params, self.params),
+            auth=merge_setting(auth, self.auth),
+            cookies=merged_cookies,
+            hooks=merge_hooks(request.hooks, self.hooks),
+        )
+        return p
+    def request(self, method, url,
+            params=None, data=None, headers=None, cookies=None, files=None,
+            auth=None, timeout=None, allow_redirects=True, proxies=None,
+            hooks=None, stream=None, verify=None, cert=None, json=None):
+        """Constructs a :class:`Request <Request>`, prepares it and sends it.
+        Returns :class:`Response <Response>` object.
+        :param method: method for the new :class:`Request` object.
+        :param url: URL for the new :class:`Request` object.
+        :param params: (optional) Dictionary or bytes to be sent in the query
+            string for the :class:`Request`.
+        :param data: (optional) Dictionary, bytes, or file-like object to send
+            in the body of the :class:`Request`.
+        :param json: (optional) json to send in the body of the
+            :class:`Request`.
+        :param headers: (optional) Dictionary of HTTP Headers to send with the
+            :class:`Request`.
+        :param cookies: (optional) Dict or CookieJar object to send with the
+            :class:`Request`.
+        :param files: (optional) Dictionary of ``'filename': file-like-objects``
+            for multipart encoding upload.
+        :param auth: (optional) Auth tuple or callable to enable
+            Basic/Digest/Custom HTTP Auth.
+        :param timeout: (optional) How long to wait for the server to send
+            data before giving up, as a float, or a :ref:`(connect timeout,
+            read timeout) <timeouts>` tuple.
+        :type timeout: float or tuple
+        :param allow_redirects: (optional) Set to True by default.
+        :type allow_redirects: bool
+        :param proxies: (optional) Dictionary mapping protocol or protocol and
+            hostname to the URL of the proxy.
+        :param stream: (optional) whether to immediately download the response
+            content. Defaults to ``False``.
+        :param verify: (optional) Either a boolean, in which case it controls whether we verify
+            the server's TLS certificate, or a string, in which case it must be a path
+            to a CA bundle to use. Defaults to ``True``.
+        :param cert: (optional) if String, path to ssl client cert file (.pem).
+            If Tuple, ('cert', 'key') pair.
+        :rtype: requests.Response
+        """
+        # Create the Request.
+        req = Request(
+            method=method.upper(),
+            url=url,
+            headers=headers,
+            files=files,
+            data=data or {},
+            json=json,
+            params=params or {},
+            auth=auth,
+            cookies=cookies,
+            hooks=hooks,
+        )
+        prep = self.prepare_request(req)
+        proxies = proxies or {}
+        settings = self.merge_environment_settings(
+            prep.url, proxies, stream, verify, cert
+        )
+        # Send the request.
+        send_kwargs = {
+            'timeout': timeout,
+            'allow_redirects': allow_redirects,
+        }
+        send_kwargs.update(settings)
+        resp = self.send(prep, **send_kwargs)
+        return resp
+    def get(self, url, **kwargs):
+        r"""Sends a GET request. Returns :class:`Response` object.
+        :param url: URL for the new :class:`Request` object.
+        :param \*\*kwargs: Optional arguments that ``request`` takes.
+        :rtype: requests.Response
+        """
+        kwargs.setdefault('allow_redirects', True)
+        return self.request('GET', url, **kwargs)
+    def options(self, url, **kwargs):
+        r"""Sends a OPTIONS request. Returns :class:`Response` object.
+        :param url: URL for the new :class:`Request` object.
+        :param \*\*kwargs: Optional arguments that ``request`` takes.
+        :rtype: requests.Response
+        """
+        kwargs.setdefault('allow_redirects', True)
+        return self.request('OPTIONS', url, **kwargs)
+    def head(self, url, **kwargs):
+        r"""Sends a HEAD request. Returns :class:`Response` object.
+        :param url: URL for the new :class:`Request` object.
+        :param \*\*kwargs: Optional arguments that ``request`` takes.
+        :rtype: requests.Response
+        """
+        kwargs.setdefault('allow_redirects', False)
+        return self.request('HEAD', url, **kwargs)
+    def post(self, url, data=None, json=None, **kwargs):
+        r"""Sends a POST request. Returns :class:`Response` object.
+        :param url: URL for the new :class:`Request` object.
+        :param data: (optional) Dictionary, bytes, or file-like object to send in the body of the :class:`Request`.
+        :param json: (optional) json to send in the body of the :class:`Request`.
+        :param \*\*kwargs: Optional arguments that ``request`` takes.
+        :rtype: requests.Response
+        """
+        return self.request('POST', url, data=data, json=json, **kwargs)
+    def put(self, url, data=None, **kwargs):
+        r"""Sends a PUT request. Returns :class:`Response` object.
+        :param url: URL for the new :class:`Request` object.
+        :param data: (optional) Dictionary, bytes, or file-like object to send in the body of the :class:`Request`.
+        :param \*\*kwargs: Optional arguments that ``request`` takes.
+        :rtype: requests.Response
+        """
+        return self.request('PUT', url, data=data, **kwargs)
+    def patch(self, url, data=None, **kwargs):
+        r"""Sends a PATCH request. Returns :class:`Response` object.
+        :param url: URL for the new :class:`Request` object.
+        :param data: (optional) Dictionary, bytes, or file-like object to send in the body of the :class:`Request`.
+        :param \*\*kwargs: Optional arguments that ``request`` takes.
+        :rtype: requests.Response
+        """
+        return self.request('PATCH', url, data=data, **kwargs)
+    def delete(self, url, **kwargs):
+        r"""Sends a DELETE request. Returns :class:`Response` object.
+        :param url: URL for the new :class:`Request` object.
+        :param \*\*kwargs: Optional arguments that ``request`` takes.
+        :rtype: requests.Response
+        """
+        return self.request('DELETE', url, **kwargs)
+    def send(self, request, **kwargs):
+        """Send a given PreparedRequest.
+        :rtype: requests.Response
+        """
+        # Set defaults that the hooks can utilize to ensure they always have
+        # the correct parameters to reproduce the previous request.
+        kwargs.setdefault('stream', self.stream)
+        kwargs.setdefault('verify', self.verify)
+        kwargs.setdefault('cert', self.cert)
+        kwargs.setdefault('proxies', self.proxies)
+        # It's possible that users might accidentally send a Request object.
+        # Guard against that specific failure case.
+        if isinstance(request, Request):
+            raise ValueError('You can only send PreparedRequests.')
+        # Set up variables needed for resolve_redirects and dispatching of hooks
+        allow_redirects = kwargs.pop('allow_redirects', True)
+        stream = kwargs.get('stream')
+        hooks = request.hooks
+        # Get the appropriate adapter to use
+        adapter = self.get_adapter(url=request.url)
+        # Start time (approximately) of the request
+        start = preferred_clock()
+        # Send the request
+        r = adapter.send(request, **kwargs)
+        # Total elapsed time of the request (approximately)
+        elapsed = preferred_clock() - start
+        r.elapsed = timedelta(seconds=elapsed)
+        # Response manipulation hooks
+        r = dispatch_hook('response', hooks, r, **kwargs)
+        # Persist cookies
+        if r.history:
+            # If the hooks create history then we want those cookies too
+            for resp in r.history:
+                extract_cookies_to_jar(self.cookies, resp.request, resp.raw)
+        extract_cookies_to_jar(self.cookies, request, r.raw)
+        # Redirect resolving generator.
+        gen = self.resolve_redirects(r, request, **kwargs)
+        # Resolve redirects if allowed.
+        history = [resp for resp in gen] if allow_redirects else []
+        # Shuffle things around if there's history.
+        if history:
+            # Insert the first (original) request at the start
+            history.insert(0, r)
+            # Get the last request made
+            r = history.pop()
+            r.history = history
+        # If redirects aren't being followed, store the response on the Request for Response.next().
+        if not allow_redirects:
+            try:
+                r._next = next(self.resolve_redirects(r, request, yield_requests=True, **kwargs))
+            except StopIteration:
+                pass
+        if not stream:
+            r.content
+        return r
+    def merge_environment_settings(self, url, proxies, stream, verify, cert):
+        """
+        Check the environment and merge it with some settings.
+        :rtype: dict
+        """
+        # Gather clues from the surrounding environment.
+        if self.trust_env:
+            # Set environment's proxies.
+            no_proxy = proxies.get('no_proxy') if proxies is not None else None
+            env_proxies = get_environ_proxies(url, no_proxy=no_proxy)
+            for (k, v) in env_proxies.items():
+                proxies.setdefault(k, v)
+            # Look for requests environment configuration and be compatible
+            # with cURL.
+            if verify is True or verify is None:
+                verify = (os.environ.get('REQUESTS_CA_BUNDLE') or
+                          os.environ.get('CURL_CA_BUNDLE'))
+        # Merge all the kwargs.
+        proxies = merge_setting(proxies, self.proxies)
+        stream = merge_setting(stream, self.stream)
+        verify = merge_setting(verify, self.verify)
+        cert = merge_setting(cert, self.cert)
+        return {'verify': verify, 'proxies': proxies, 'stream': stream,
+                'cert': cert}
+    def get_adapter(self, url):
+        """
+        Returns the appropriate connection adapter for the given URL.
+        :rtype: requests.adapters.BaseAdapter
+        """
+        for (prefix, adapter) in self.adapters.items():
+            if url.lower().startswith(prefix):
+                return adapter
+        # Nothing matches :-/
+        raise InvalidSchema("No connection adapters were found for '%s'" % url)
+    def close(self):
+        """Closes all adapters and as such the session"""
+        for v in self.adapters.values():
+            v.close()
+    def mount(self, prefix, adapter):
+        """Registers a connection adapter to a prefix.
+        Adapters are sorted in descending order by prefix length.
+        """
+        self.adapters[prefix] = adapter
+        keys_to_move = [k for k in self.adapters if len(k) < len(prefix)]
+        for key in keys_to_move:
+            self.adapters[key] = self.adapters.pop(key)
+    def __getstate__(self):
+        state = dict((attr, getattr(self, attr, None)) for attr in self.__attrs__)
+        return state
+    def __setstate__(self, state):
+        for attr, value in state.items():
+            setattr(self, attr, value)
+def session():
+    """
+    Returns a :class:`Session` for context-management.
+    :rtype: Session
+    """
+    return Session()