You are ArchitecturalBuilder, a System Two patch synthesizer in Active Focus mode. Output exact SEARCH/REPLACE blocks (<<<<<<< SEARCH ... ======= ... >>>>>>> REPLACE), one per hunk, no line numbers, no prose, no markdown fences. Emit the blocks FIRST, before any other text, so a truncated output still carries the patch. Prefix each block with its repo-relative target file path on its own line. Copy every SEARCH block byte-for-byte from the shown CODE CONTEXT (exact indentation and punctuation); never reconstruct code from memory. Stop immediately after the last >>>>>>> REPLACE line; no trailing commentary.
BUDGET: fit the ENTIRE response in 700 tokens; if several hunks are needed, output the most critical first.

ISSUE:
Getting http://.example.com raises UnicodeError
Attempting to get e.g. `http://.example.com` results in a `UnicodeError`. It seems like the intention so far has been to raise `InvalidUrl` instead (see e.g. [this line](https://github.com/psf/requests/blob/ca6f9af5dba09591007b15a7368bc0f006b7cc50/requests/models.py#L401)).

I see there was some hesitation in fixing a similar issue (#4168) and would like to add that even catching the error just to rethrow as a requests exception would be beneficial.

## Expected Result

Based on PR #774: `InvalidUrl: URL has an invalid label.`

## Actual Result

`UnicodeError: encoding with 'idna' codec failed (UnicodeError: label empty or too long)`

## Reproduction Steps

```python3
import requests
requests.get("http://.example.com")
```

## System Information

    $ python -m requests.help

```
{
  "chardet": {
    "version": "3.0.4"
  },
  "cryptography": {
    "version": "2.8"
  },
  "idna": {
    "version": "2.8"
  },
  "implementation": {
    "name": "CPython",
    "version": "3.8.0"
  },
  "platform": {
    "release": "5.3.0-40-generic",
    "system": "Linux"
  },
  "pyOpenSSL": {
    "openssl_version": "1010104f",
    "version": "19.1.0"
  },
  "requests": {
    "version": "2.23.0"
  },
  "system_ssl": {
    "version": "1010103f"
  },
  "urllib3": {
    "version": "1.25.8"
  },
  "using_pyopenssl": true
}
```

CODE CONTEXT:
TOP-1 FULL FILE requests/help.py:
"""Module containing bug report helper(s)."""
from __future__ import print_function

import json
import platform
import sys
import ssl

import idna
import urllib3

from . import __version__ as requests_version

try:
    import charset_normalizer
except ImportError:
    charset_normalizer = None

try:
    import chardet
except ImportError:
    chardet = None

try:
    from urllib3.contrib import pyopenssl
except ImportError:
    pyopenssl = None
    OpenSSL = None
    cryptography = None
else:
    import OpenSSL
    import cryptography


def _implementation():
    """Return a dict with the Python implementation and version.

    Provide both the name and the version of the Python implementation
    currently running. For example, on CPython 2.7.5 it will return
    {'name': 'CPython', 'version': '2.7.5'}.

    This function works best on CPython and PyPy: in particular, it probably
    doesn't work for Jython or IronPython. Future investigation should be done
    to work out the correct shape of the code for those platforms.
    """
    implementation = platform.python_implementation()

    if implementation == 'CPython':
        implementation_version = platform.python_version()
    elif implementation == 'PyPy':
        implementation_version = '%s.%s.%s' % (sys.pypy_version_info.major,
                                               sys.pypy_version_info.minor,
                                               sys.pypy_version_info.micro)
        if sys.pypy_version_info.releaselevel != 'final':
            implementation_version = ''.join([
                implementation_version, sys.pypy_version_info.releaselevel
            ])
    elif implementation == 'Jython':
        implementation_version = platform.python_version()  # Complete Guess
    elif implementation == 'IronPython':
        implementation_version = platform.python_version()  # Complete Guess
    else:
        implementation_version = 'Unknown'

    return {'name': implementation, 'version': implementation_version}


def info():
    """Generate information for a bug report."""
    try:
        platform_info = {
            'system': platform.system(),
            'release': platform.release(),
        }
    except IOError:
        platform_info = {
            'system': 'Unknown',
            'release': 'Unknown',
        }

    implementation_info = _implementation()
    urllib3_info = {'version': urllib3.__version__}
    charset_normalizer_info = {'version': None}
    chardet_info = {'version': None}
    if charset_normalizer:
        charset_normalizer_info = {'version': charset_normalizer.__version__}
    if chardet:
        chardet_info = {'version': chardet.__version__}

    pyopenssl_info = {
        'version': None,
        'openssl_version': '',
    }
    if OpenSSL:
        pyopenssl_info = {
            'version': OpenSSL.__version__,
            'openssl_version': '%x' % OpenSSL.SSL.OPENSSL_VERSION_NUMBER,
        }
    cryptography_info = {
        'version': getattr(cryptography, '__version__', ''),
    }
    idna_info = {
        'version': getattr(idna, '__version__', ''),
    }

    system_ssl = ssl.OPENSSL_VERSION_NUMBER
    system_ssl_info = {
        'version': '%x' % system_ssl if system_ssl is not None else ''
    }

    return {
        'platform': platform_info,
        'implementation': implementation_info,
        'system_ssl': system_ssl_info,
        'using_pyopenssl': pyopenssl is not None,
        'using_charset_normalizer': chardet is None,
        'pyOpenSSL': pyopenssl_info,
        'urllib3': urllib3_info,
        'chardet': chardet_info,
        'charset_normalizer': charset_normalizer_info,
        'cryptography': cryptography_info,
        'idna': idna_info,
        'requests': {
            'version': requests_version,
        },
    }


def main():
    """Pretty-print the bug information as JSON."""
    print(json.dumps(info(), sort_keys=True, indent=2))


if __name__ == '__main__':
    main()


requests/help.py:
"""Module containing bug report helper(s)."""
from __future__ import print_function

import json
import platform
import sys
import ssl

import idna
import urllib3

from . import __version__ as requests_version

try:
    import charset_normalizer
except ImportError:
    charset_normalizer = None

try:
    import chardet
except ImportError:
    chardet = None

try:
    from urllib3.contrib import pyopenssl
except ImportError:
    pyopenssl = None
    OpenSSL = None
    cryptography = None
else:
    import OpenSSL
    import cryptography


def _implementation():
    """Return a dict with the Python implementation and version.

    Provide both the name and the version of the Python implementation
    currently running. For example, on CPython 2.7.5 it will return
    {'name': 'CPython', 'version': '2.7.5'}.

    This function works best on CPython and PyPy: in particular, it probably
    doesn't work for Jython or IronPython. Future investigation should be done
    to work out the correct shape of the code for those platforms.
    """
    implementation = platform.python_implementation()

    if implementation == 'CPython':
        implementation_version = platform.python_version()
    elif implementation == 'PyPy':
        implementation_version = '%s.%s.%s' % (sys.pypy_version_info.major,
                                               sys.pypy_version_info.minor,
                                               sys.pypy_version_info.micro)
        if sys.pypy_version_info.releaselevel != 'final':
            implementation_version = ''.join([
                implementation_version, sys.pypy_version_info.releaselevel
            ])
    elif implementation == 'Jython':
        implementation_version = platform.python_version()  # Complete Guess
    elif implementation == 'IronPython':
        implementation_version = platform.python_version()  # Complete Guess
    else:
        implementation_version = 'Unknown'

    return {'name': implementation, 'version': implementation_version}


def info():
    """Generate information for a bug report."""
    try:
        platform_info = {
            'system': platform.system(),
            'release': platform.release(),
        }
    except IOError:
        platform_info = {
            'system': 'Unknown',
            'release': 'Unknown',
        }

    implementation_info = _implementation()
    urllib3_info = {'version': urllib3.__version__}
    charset_normalizer_info = {'version': None}
    chardet_info = {'version': None}
    if charset_normalizer:
        charset_normalizer_info = {'version': charset_normalizer.__version__}
    if chardet:
        chardet_info = {'version': chardet.__version__}

    pyopenssl_info = {
        'version': None,
        'openssl_version': '',
    }
    if OpenSSL:
        pyopenssl_info = {
            'version': OpenSSL.__version__,
            'openssl_version': '%x' % OpenSSL.SSL.OPENSSL_VERSION_NUMBER,
        }
    cryptography_info = {
        'version': getattr(cryptography, '__version__', ''),
    }
    idna_info = {
        'version': getattr(idna, '__version__', ''),
    }

    system_ssl = ssl.OPENSSL_VERSION_NUMBER
    system_ssl_info = {
        'version': '%x' % system_ssl if system_ssl is not None else ''
    }

    return {
        'platform': platform_info,
        'implementation': implementation_info,
        'system_ssl': system_ssl_info,
        'using_pyopenssl': pyopenssl is not None,
        'using_charset_normalizer': chardet is None,
        'pyOpenSSL': pyopenssl_info,
        'urllib3': urllib3_info,
        'chardet': chardet_info,
        'charset_normalizer': charset_normalizer_info,
        'cryptography': cryptography_info,
        'idna': idna_info,
        'requests': {
            'version': requests_version,
        },
    }


def main():
    """Pretty-print the bug information as JSON."""
    print(json.dumps(info(), sort_keys=True, indent=2))


if __name__ == '__main__':
    main()


requests/__init__.py:
# -*- coding: utf-8 -*-

#   __
#  /__)  _  _     _   _ _/   _
# / (   (- (/ (/ (- _)  /  _)
#          /

"""
Requests HTTP Library
~~~~~~~~~~~~~~~~~~~~~

Requests is an HTTP library, written in Python, for human beings.
Basic GET usage:

   >>> import requests
   >>> r = requests.get('https://www.python.org')
   >>> r.status_code
   200
   >>> b'Python is a programming language' in r.content
   True

... or POST:

   >>> payload = dict(key1='value1', key2='value2')
   >>> r = requests.post('https://httpbin.org/post', data=payload)
   >>> print(r.text)
   {
     ...
     "form": {
       "key1": "value1",
       "key2": "value2"
     },
     ...
   }

The other HTTP methods are supported - see `requests.api`. Full documentation
is at <https://requests.readthedocs.io>.

:copyright: (c) 2017 by Kenneth Reitz.
:license: Apache 2.0, see LICENSE for more details.
"""

import urllib3
import warnings
from .exceptions import RequestsDependencyWarning

try:
    from charset_normalizer import __version__ as charset_normalizer_version
except ImportError:
    charset_normalizer_version = None

try:
    from chardet import __version__ as chardet_version
except ImportError:
    chardet_version = None

def check_compatibility(urllib3_version, chardet_version, charset_normalizer_version):
    urllib3_version = urllib3_version.split('.')
    assert urllib3_version != ['dev']  # Verify urllib3 isn't installed from git.

    # Sometimes, urllib3 only reports its version as 16.1.
    if len(urllib3_version) == 2:
        urllib3_version.append('0')

    # Check urllib3 for compatibility.
    major, minor, patch = urllib3_version  # noqa: F811
    major, minor, patch = int(major), int(minor), int(patch)
    # urllib3 >= 1.21.1, <= 1.26
    assert major == 1
    assert minor >= 21
    assert minor <= 26

    # Check charset_normalizer for compatibility.
    if chardet_version:
        major, minor, patch = chardet_version.split('.')[:3]
        major, minor, patch = int(major), int(minor), int(patch)
        # chardet_version >= 3.0.2, < 5.0.0
        assert (3, 0, 2) <= (major, minor, patch) < (5, 0, 0)
    elif charset_normalizer_version:
        major, minor, patch = charset_normalizer_version.split('.')[:3]
        major, minor, patch = int(major), int(minor), int(patch)
        # charset_normalizer >= 2.0.0 < 3.0.0
        assert (2, 0, 0) <= (major, minor, patch) < (3, 0, 0)
    else:
        raise Exception("You need either charset_normalizer or chardet installed")

def _check_cryptography(cryptography_version):
    # cryptography < 1.3.4
    try:
        cryptography_version = list(map(int, cryptography_version.split('.')))
    except ValueError:
        return

    if cryptography_version < [1, 3, 4]:
        warning = 'Old version of cryptography ({}) may cause slowdown.'.format(cryptography_version)
        warnings.warn(warning, RequestsDependencyWarning)

# Check imported dependencies for compatibility.
try:
    check_compatibility(urllib3.__version__, chardet_version, charset_normalizer_version)
except (AssertionError, ValueError):
    warnings.warn("urllib3 ({}) or chardet ({})/charset_normalizer ({}) doesn't match a supported "
                  "version!".format(urllib3.__version__, chardet_version, charset_normalizer_version),
                  RequestsDependencyWarning)

# Attempt to enable urllib3's fallback for SNI support
# if the standard library doesn't support SNI or the
# 'ssl' library isn't available.
try:
    try:
        import ssl
    except ImportError:
        ssl = None

    if not getattr(ssl, "HAS_SNI", False):
        from urllib3.contrib import pyopenssl
        pyopenssl.inject_into_urllib3()

        # Check cryptography version
        from cryptography import __version__ as cryptography_version
        _check_cryptography(cryptography_version)
except ImportError:
    pass

# urllib3's DependencyWarnings should be silenced.
from urllib3.exceptions import DependencyWarning
warnings.simplefilter('ignore', DependencyWarning)

from .__version__ import __title__, __description__, __url__, __version__
from .__version__ import __build__, __author__, __author_email__, __license__
from .__version__ import __copyright__, __cake__

from . import utils
from . import packages
from .models import Request, Response, PreparedRequest
from .api import request, get, head, post, patch, put, delete, options
from .sessions import session, Session
from .status_codes import codes
from .exceptions import (
    RequestException, Timeout, URLRequired,
    TooManyRedirects, HTTPError, ConnectionError,
    FileModeWarning, ConnectTimeout, ReadTimeout, JSONDecodeError
)

# Set default logging handler to avoid "No handler found" warnings.
import logging
from logging import NullHandler

logging.getLogger(__name__).addHandler(NullHandler())

# FileModeWarnings go off per the default.
warnings.simplefilter('default', FileModeWarning, append=True)


requests/exceptions.py:
# -*- coding: utf-8 -*-

"""
requests.exceptions
~~~~~~~~~~~~~~~~~~~

This module contains the set of Requests' exceptions.
"""
from urllib3.exceptions import HTTPError as BaseHTTPError

from .compat import JSONDecodeError as CompatJSONDecodeError


class RequestException(IOError):
    """There was an ambiguous exception that occurred while handling your
    request.
    """

    def __init__(self, *args, **kwargs):
        """Initialize RequestException with `request` and `response` objects."""
        response = kwargs.pop('response', None)
        self.response = response
        self.request = kwargs.pop('request', None)
        if (response is not None and not self.request and
                hasattr(response, 'request')):
            self.request = self.response.request
        super(RequestException, self).__init__(*args, **kwargs)


class InvalidJSONError(RequestException):
    """A JSON error occurred."""


class JSONDecodeError(InvalidJSONError, CompatJSONDecodeError):
    """Couldn't decode the text into json"""


class HTTPError(RequestException):
    """An HTTP error occurred."""


class ConnectionError(RequestException):
    """A Connection error occurred."""


class ProxyError(ConnectionError):
    """A proxy error occurred."""


class SSLError(ConnectionError):
    """An SSL error occurred."""


class Timeout(RequestException):
    """The request timed out.

    Catching this error will catch both
    :exc:`~requests.exceptions.ConnectTimeout` and
    :exc:`~requests.exceptions.ReadTimeout` errors.
    """


class ConnectTimeout(ConnectionError, Timeout):
    """The request timed out while trying to connect to the remote server.

    Requests that produced this error are safe to retry.
    """


class ReadTimeout(Timeout):
    """The server did not send any data in the allotted amount of time."""


class URLRequired(RequestException):
    """A valid URL is required to make a request."""


class TooManyRedirects(RequestException):
    """Too many redirects."""


class MissingSchema(RequestException, ValueError):
    """The URL schema (e.g. http or https) is missing."""


class InvalidSchema(RequestException, ValueError):
    """See defaults.py for valid schemas."""


class InvalidURL(RequestException, ValueError):
    """The URL provided was somehow invalid."""


class InvalidHeader(RequestException, ValueError):
    """The header value provided was somehow invalid."""


class InvalidProxyURL(InvalidURL):
    """The proxy URL provided is invalid."""


class ChunkedEncodingError(RequestException):
    """The server declared chunked encoding but sent an invalid chunk."""


class ContentDecodingError(RequestException, BaseHTTPError):
    """Failed to decode response content."""


class StreamConsumedError(RequestException, TypeError):
    """The content for this response was already consumed."""


class RetryError(RequestException):
    """Custom retries logic failed"""


class UnrewindableBodyError(RequestException):
    """Requests encountered an error when trying to rewind a body."""

# Warnings


class RequestsWarning(Warning):
    """Base warning for Requests."""


class FileModeWarning(RequestsWarning, DeprecationWarning):
    """A file was opened in text mode, but Requests determined its binary length."""


class RequestsDependencyWarning(RequestsWarning):
    """An imported dependency doesn't match the expected version range."""


requests/utils.py:
# -*- coding: utf-8 -*-

"""
requests.utils
~~~~~~~~~~~~~~

This module provides utility functions that are used within Requests
that are also useful for external consumption.
"""

import codecs
import contextlib
import io
import os
import re
import socket
import struct
import sys
import tempfile
import warnings
import zipfile
from collections import OrderedDict
from urllib3.util import make_headers

from .__version__ import __version__
from . import certs
# to_native_string is unused here, but imported here for backwards compatibility
from ._internal_utils import to_native_string
from .compat import parse_http_list as _parse_list_header
from .compat import (
    quote, urlparse, bytes, str, unquote, getproxies,
    proxy_bypass, urlunparse, basestring, integer_types, is_py3,
    proxy_bypass_environment, getproxies_environment, Mapping)
from .cookies import cookiejar_from_dict
from .structures import CaseInsensitiveDict
from .exceptions import (
    InvalidURL, InvalidHeader, FileModeWarning, UnrewindableBodyError)

NETRC_FILES = ('.netrc', '_netrc')

DEFAULT_CA_BUNDLE_PATH = certs.where()

DEFAULT_PORTS = {'http': 80, 'https': 443}

# Ensure that ', ' is used to preserve previous delimiter behavior.
DEFAULT_ACCEPT_ENCODING = ", ".join(
    re.split(r",\s*", make_headers(accept_encoding=True)["accept-encoding"])
)


if sys.platform == 'win32':
    # provide a proxy_bypass version on Windows without DNS lookups

    def proxy_bypass_registry(host):
        try:
            if is_py3:
                import winreg
            else:
                import _winreg as winreg
        except ImportError:
            return False

        try:
            internetSettings = winreg.OpenKey(winreg.HKEY_CURRENT_USER,
                r'Software\Microsoft\Windows\CurrentVersion\Internet Settings')
            # ProxyEnable could be REG_SZ or REG_DWORD, normalizing it
            proxyEnable = int(winreg.QueryValueEx(internetSettings,
                                              'ProxyEnable')[0])
            # ProxyOverride is almost always a string
            proxyOverride = winreg.QueryValueEx(internetSettings,
                                                'ProxyOverride')[0]
        except OSError:
            return False
        if not proxyEnable or not proxyOverride:
            return False

        # make a check value list from the registry entry: replace the
        # '<local>' string by the localhost entry and the corresponding
        # canonical entry.
        proxyOverride = proxyOverride.split(';')
        # now check if we match one of the registry values.
        for test in proxyOverride:
            if test == '<local>':
                if '.' not in host:
                    return True
            test = test.replace(".", r"\.")     # mask dots
            test = test.replace("*", r".*")     # change glob sequence
            test = test.replace("?", r".")      # change glob char
            if re.match(test, host, re.I):
                return True
        return False

    def proxy_bypass(host):  # noqa
        """Return True, if the host should be bypassed.

        Checks proxy settings gathered from the environment, if specified,
        or the registry.
        """
        if getproxies_environment():
            return proxy_bypass_environment(host)
        else:
            return proxy_bypass_registry(host)


def dict_to_sequence(d):
    """Returns an internal sequence dictionary update."""

    if hasattr(d, 'items'):
        d = d.items()

    return d


def super_len(o):
    total_length = None
    current_position = 0

    if hasattr(o, '__len__'):
        total_length = len(o)

    elif hasattr(o, 'len'):
        total_length = o.len

    elif hasattr(o, 'fileno'):
        try:
            fileno = o.fileno()
        except (io.UnsupportedOperation, AttributeError):
            # AttributeError is a surprising exception, seeing as how we've just checked
            # that `hasattr(o, 'fileno')`.  It happens for objects obtained via
            # `Tarfile.extractfile()`, per issue 5229.
            pass
        else:
            total_length = os.fstat(fileno).st_size

            # Having used fstat to determine the file length, we need to
            # confirm that this file was opened up in binary mode.
            if 'b' not in o.mode:
                warnings.warn((
                    "Requests has determined the content-length for this "
                    "request using the binary size of the file: however, the "
                    "file has been opened in text mode (i.e. without the 'b' "
                    "flag in the mode). This may lead to an incorrect "
                    "content-length. In Requests 3.0, support will be removed "
                    "for files in text mode."),
                    FileModeWarning
                )

    if hasattr(o, 'tell'):
        try:
            current_position = o.tell()
        except (OSError, IOError):
            # This can happen in some weird situations, such as when the file
            # is actually a special file descriptor like stdin. In this
            # instance, we don't know what the length is, so set it to zero and
            # let requests chunk it instead.
            if total_length is not None:
                current_position = total_length
        else:
            if hasattr(o, 'seek') and total_length is None:
                # StringIO and BytesIO have seek but no usable fileno
                try:
                    # seek to end of file
                    o.seek(0, 2)
                    total_length = o.tell()

                    # seek back to current position to support
                    # partially read file-like objects
                    o.seek(current_position or 0)
                except (OSError, IOError):
                    total_length = 0

    if total_length is None:
        total_length = 0

    return max(0, total_length - current_position)


def get_netrc_auth(url, raise_errors=False):
    """Returns the Requests tuple auth for a given url from netrc."""

    netrc_file = os.environ.get('NETRC')
    if netrc_file is not None:
        netrc_locations = (netrc_file,)
    else:
        netrc_locations = ('~/{}'.format(f) for f in NETRC_FILES)

    try:
        from netrc import netrc, NetrcParseError

        netrc_path = None

        for f in netrc_locations:
            try:
                loc = os.path.expanduser(f)
            except KeyError:
                # os.path.expanduser can fail when $HOME is undefined and
                # getpwuid fails. See https://bugs.python.org/issue20164 &
                # https://github.com/psf/requests/issues/1846
                return

            if os.path.exists(loc):
                netrc_path = loc
                break

        # Abort early if there isn't one.
        if netrc_path is None:
            return

        ri = urlparse(url)

        # Strip port numbers from netloc. This weird `if...encode`` dance is
        # used for Python 3.2, which doesn't support unicode literals.
        splitstr = b':'
        if isinstance(url, str):
            splitstr = splitstr.decode('ascii')
        host = ri.netloc.split(splitstr)[0]

        try:
            _netrc = netrc(netrc_path).authenticators(host)
            if _netrc:
                # Return with login / password
                login_i = (0 if _netrc[0] else 1)
                return (_netrc[login_i], _netrc[2])
        except (NetrcParseError, IOError):
            # If there was a parsing error or a permissions issue reading the file,
            # we'll just skip netrc auth unless explicitly asked to raise errors.
            if raise_errors:
                raise

    # App Engine hackiness.
    except (ImportError, AttributeError):
        pass


def guess_filename(obj):
    """Tries to guess the filename of the given object."""
    name = getattr(obj, 'name', None)
    if (name and isinstance(name, bas

requests/sessions.py:
# -*- coding: utf-8 -*-

"""
requests.sessions
~~~~~~~~~~~~~~~~~

This module provides a Session object to manage and persist settings across
requests (cookies, auth, proxies).
"""
import os
import sys
import time
from datetime import timedelta
from collections import OrderedDict

from .auth import _basic_auth_str
from .compat import cookielib, is_py3, urljoin, urlparse, Mapping
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, DEFAULT_PORTS
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, resolve_proxies
)

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 sys.platform == 'win32':
    try:  # Python 3.4+
        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 should_strip_auth(self, old_url, new_url):
        """Decide whether Authorization header should be removed when redirecting"""
        old_parsed = urlparse(old_url)
        new_parsed = urlparse(new_url)
        if old_parsed.hostname != new_parsed.hostname:
            return True
        # Special case: allow http -> https redirect when using the standard
        # ports. This isn't specified by RFC 7235, but is kept to avoid
        # breaking backwards compatibility with older versions of requests
        # that allowed any redirects on the same host.
        if (old_parsed.scheme == 'http' and old_parsed.port in (80, None)
                and new_parsed.scheme == 'https' and new_parsed.port in (443, None)):
            return False

        # Handle default port usage corresponding to scheme.
        changed_port = old_parsed.port != new_parsed.port
        changed_scheme = old_parsed.scheme != new_parsed.scheme
        default_port = (DEFAULT_PORTS.get(old_parsed.scheme, None), None)
        if (not changed_scheme and old_parsed.port in default_port
                and new_parsed.port in default_port):
            return False

        # Standard case: root URI must match
        return changed_port or changed_scheme

    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)
        previous_fragment = urlparse(req.url).fragment
        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 {} redirects.'.format(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 = ':'.join([to_native_string(parsed_rurl.scheme), url])

            # Normalize url case and attach previous fragment if needed (RFC 7231 7.1.2)
            parsed = urlparse(url)
            if parsed.fragment == '' and previous_fragment:
                parsed = parsed._replace(fragment=previous_fragment)
            elif parsed.fragment:
                previous_fragment = parsed.fragment
            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/psf/requests/issues/1084
            if resp.status_code not in (codes.temporary_redirect, codes.permanent_redirect):
                # https://github.com/psf/requests/issues/3490
                purged_hea

ROUND: 1