text: import base64
  import calendar
  import datetime
  import re
  import sys
  import unicodedata
  import warnings
  from binascii import Error as BinasciiError
  from email.utils import formatdate
  from urllib.parse import (
      quote, quote_plus, unquote, unquote_plus, urlencode as original_urlencode,
      urlparse,
  )
  
  from django.core.exceptions import TooManyFieldsSent
  from django.utils import six
  from django.utils.datastructures import MultiValueDict
  from django.utils.deprecation import RemovedInDjango21Warning
  from django.utils.encoding import force_bytes, force_str, force_text
  from django.utils.functional import keep_lazy_text
  
  # based on RFC 7232, Appendix C
  ETAG_MATCH = re.compile(r'''
      \A(      # start of string and capture group
      (?:W/)?  # optional weak indicator
      "        # opening quote
      [^"]*    # any sequence of non-quote characters
      "        # end quote
      )\Z      # end of string and capture group
  ''', re.X)
  
  MONTHS = 'jan feb mar apr may jun jul aug sep oct nov dec'.split()
  __D = r'(?P<day>\d{2})'
  __D2 = r'(?P<day>[ \d]\d)'
  __M = r'(?P<mon>\w{3})'
  __Y = r'(?P<year>\d{4})'
  __Y2 = r'(?P<year>\d{2})'
  __T = r'(?P<hour>\d{2}):(?P<min>\d{2}):(?P<sec>\d{2})'
  RFC1123_DATE = re.compile(r'^\w{3}, %s %s %s %s GMT$' % (__D, __M, __Y, __T))
  RFC850_DATE = re.compile(r'^\w{6,9}, %s-%s-%s %s GMT$' % (__D, __M, __Y2, __T))
  ASCTIME_DATE = re.compile(r'^\w{3} %s %s %s %s$' % (__M, __D2, __T, __Y))
  
  RFC3986_GENDELIMS = str(":/?#[]@")
  RFC3986_SUBDELIMS = str("!$&'()*+,;=")
  
  FIELDS_MATCH = re.compile('[&;]')
  
  
  @keep_lazy_text
  def urlquote(url, safe='/'):
      """
      A version of Python's urllib.quote() function that can operate on unicode
      strings. The url is first UTF-8 encoded before quoting. The returned string
      can safely be used as part of an argument to a subsequent iri_to_uri() call
      without double-quoting occurring.
      """
      return force_text(quote(force_str(url), force_str(safe)))
  
  
  @keep_lazy_text
  def urlquote_plus(url, safe=''):
      """
      A version of Python's urllib.quote_plus() function that can operate on
      unicode strings. The url is first UTF-8 encoded before quoting. The
      returned string can safely be used as part of an argument to a subsequent
      iri_to_uri() call without double-quoting occurring.
      """
      return force_text(quote_plus(force_str(url), force_str(safe)))
  
  
  @keep_lazy_text
  def urlunquote(quoted_url):
      """
      A wrapper for Python's urllib.unquote() function that can operate on
      the result of django.utils.http.urlquote().
      """
      return force_text(unquote(force_str(quoted_url)))
  
  
  @keep_lazy_text
  def urlunquote_plus(quoted_url):
      """
      A wrapper for Python's urllib.unquote_plus() function that can operate on
      the result of django.utils.http.urlquote_plus().
      """
      return force_text(unquote_plus(force_str(quoted_url)))
  
  
  def urlencode(query, doseq=0):
      """
      A version of Python's urllib.urlencode() function that can operate on
      unicode strings. The parameters are first cast to UTF-8 encoded strings and
      then encoded as per normal.
      """
      if isinstance(query, MultiValueDict):
          query = query.lists()
      elif hasattr(query, 'items'):
          query = query.items()
      return original_urlencode(
          [(force_str(k),
           [force_str(i) for i in v] if isinstance(v, (list, tuple)) else force_str(v))
              for k, v in query],
          doseq)
  
  
  def cookie_date(epoch_seconds=None):
      """
      Formats the time to ensure compatibility with Netscape's cookie standard.
  
      Accepts a floating point number expressed in seconds since the epoch, in
      UTC - such as that outputted by time.time(). If set to None, defaults to
      the current time.
  
      Outputs a string in the format 'Wdy, DD-Mon-YYYY HH:MM:SS GMT'.
      """
      rfcdate = formatdate(epoch_seconds)
      return '%s-%s-%s GMT' % (rfcdate[:7], rfcdate[8:11], rfcdate[12:25])
  
  
  def http_date(epoch_seconds=None):
      """
      Formats the time to match the RFC1123 date format as specified by HTTP
      RFC7231 section 7.1.1.1.
  
      Accepts a floating point number expressed in seconds since the epoch, in
      UTC - such as that outputted by time.time(). If set to None, defaults to
      the current time.
  
      Outputs a string in the format 'Wdy, DD Mon YYYY HH:MM:SS GMT'.
      """
      return formatdate(epoch_seconds, usegmt=True)
  
  
  def parse_http_date(date):
      """
      Parses a date format as specified by HTTP RFC7231 section 7.1.1.1.
  
      The three formats allowed by the RFC are accepted, even if only the first
      one is still in widespread use.
  
      Returns an integer expressed in seconds since the epoch, in UTC.
      """
      # emails.Util.parsedate does the job for RFC1123 dates; unfortunately
      # RFC7231 makes it mandatory to support RFC850 dates too. So we roll
      # our own RFC-compliant parsing.
      for regex in RFC1123_DATE, RFC850_DATE, ASCTIME_DATE:
          m = regex.match(date)
          if m is not None:
              break
      else:
          raise ValueError("%r is not in a valid HTTP date format" % date)
      try:
          year = int(m.group('year'))
          if year < 100:
              if year < 70:
                  year += 2000
              else:
                  year += 1900
          month = MONTHS.index(m.group('mon').lower()) + 1
          day = int(m.group('day'))
          hour = int(m.group('hour'))
          min = int(m.group('min'))
          sec = int(m.group('sec'))
          result = datetime.datetime(year, month, day, hour, min, sec)
          return calendar.timegm(result.utctimetuple())
      except Exception:
          six.reraise(ValueError, ValueError("%r is not a valid date" % date), sys.exc_info()[2])
  
  
  def parse_http_date_safe(date):
      """
      Same as parse_http_date, but returns None if the input is invalid.
      """
      try:
          return parse_http_date(date)
      except Exception:
          pass
  
  
  # Base 36 functions: useful for generating compact URLs
  
  def base36_to_int(s):
      """
      Converts a base 36 string to an ``int``. Raises ``ValueError` if the
      input won't fit into an int.
      """
      # To prevent overconsumption of server resources, reject any
      # base36 string that is longer than 13 base36 digits (13 digits
      # is sufficient to base36-encode any 64-bit integer)
      if len(s) > 13:
          raise ValueError("Base36 input too large")
      return int(s, 36)
  
  
  def int_to_base36(i):
      """
      Converts an integer to a base36 string
      """
      char_set = '0123456789abcdefghijklmnopqrstuvwxyz'
      if i < 0:
          raise ValueError("Negative base36 conversion input.")
      if i < 36:
          return char_set[i]
      b36 = ''
      while i != 0:
          i, n = divmod(i, 36)
          b36 = char_set[n] + b36
      return b36
  
  
  def urlsafe_base64_encode(s):
      """
      Encodes a bytestring in base64 for use in URLs, stripping any trailing
      equal signs.
      """
      return base64.urlsafe_b64encode(s).rstrip(b'\n=')
  
  
  def urlsafe_base64_decode(s):
      """
      Decodes a base64 encoded string, adding back any trailing equal signs that
      might have been stripped.
      """
      s = force_bytes(s)
      try:
          return base64.urlsafe_b64decode(s.ljust(len(s) + len(s) % 4, b'='))
      except (LookupError, BinasciiError) as e:
          raise ValueError(e)
  
  
  def parse_etags(etag_str):
      """
      Parse a string of ETags given in an If-None-Match or If-Match header as
      defined by RFC 7232. Return a list of quoted ETags, or ['*'] if all ETags
      should be matched.
      """
      if etag_str.strip() == '*':
          return ['*']
      else:
          # Parse each ETag individually, and return any that are valid.
          etag_matches = (ETAG_MATCH.match(etag.strip()) for etag in etag_str.split(','))
          return [match.group(1) for match in etag_matches if match]
  
  
  def quote_etag(etag_str):
      """
      If the provided string is already a quoted ETag, return it. Otherwise, wrap
      the string in quotes, making it a strong ETag.
      """
      if ETAG_MATCH.match(etag_str):
          return etag_str
      else:
          return '"%s"' % etag_str
  
  
  def is_same_domain(host, pattern):
      """
      Return ``True`` if the host is either an exact match or a match
      to the wildcard pattern.
  
      Any pattern beginning with a period matches a domain and all of its
      subdomains. (e.g. ``.example.com`` matches ``example.com`` and
      ``foo.example.com``). Anything else is an exact string match.
      """
      if not pattern:
          return False
  
      pattern = pattern.lower()
      return (
          pattern[0] == '.' and (host.endswith(pattern) or host == pattern[1:]) or
          pattern == host
      )
  
  
  def is_safe_url(url, host=None, allowed_hosts=None, require_https=False):
      """
      Return ``True`` if the url is a safe redirection (i.e. it doesn't point to
      a different host and uses a safe scheme).
  
      Always returns ``False`` on an empty url.
  
      If ``require_https`` is ``True``, only 'https' will be considered a valid
      scheme, as opposed to 'http' and 'https' with the default, ``False``.
      """
      if url is not None:
          url = url.strip()
      if not url:
          return False
      if allowed_hosts is None:
          allowed_hosts = set()
      if host:
          warnings.warn(
              "The host argument is deprecated, use allowed_hosts instead.",
              RemovedInDjango21Warning,
              stacklevel=2,
          )
          # Avoid mutating the passed in allowed_hosts.
          allowed_hosts = allowed_hosts | {host}
      # Chrome treats \ completely as / in paths but it could be part of some
      # basic auth credentials so we need to check both URLs.
      return (_is_safe_url(url, allowed_hosts, require_https=require_https) and
              _is_safe_url(url.replace('\\', '/'), allowed_hosts, require_https=require_https))
  
  
  def _is_safe_url(url, allowed_hosts, require_https=False):
      # Chrome considers any URL with more than two slashes to be absolute, but
      # urlparse is not so flexible. Treat any url with three slashes as unsafe.
      if url.startswith('///'):
          return False
      url_info = urlparse(url)
      # Forbid URLs like http:///example.com - with a scheme, but without a hostname.
      # In that URL, example.com is not the hostname but, a path component. However,
      # Chrome will still consider example.com to be the hostname, so we must not
      # allow this syntax.
      if not url_info.netloc and url_info.scheme:
          return False
      # Forbid URLs that start with control characters. Some browsers (like
      # Chrome) ignore quite a few control characters at the start of a
      # URL and might consider the URL as scheme relative.
      if unicodedata.category(url[0])[0] == 'C':
          return False
      scheme = url_info.scheme
      # Consider URLs without a scheme (e.g. //example.com/p) to be http.
      if not url_info.scheme and url_info.netloc:
          scheme = 'http'
      valid_schemes = ['https'] if require_https else ['http', 'https']
      return ((not url_info.netloc or url_info.netloc in allowed_hosts) and
              (not scheme or scheme in valid_schemes))
  
  
  def limited_parse_qsl(qs, keep_blank_values=False, encoding='utf-8',
                        errors='replace', fields_limit=None):
      """
      Return a list of key/value tuples parsed from query string.
  
      Copied from urlparse with an additional "fields_limit" argument.
      Copyright (C) 2013 Python Software Foundation (see LICENSE.python).
  
      Arguments:
  
      qs: percent-encoded query string to be parsed
  
      keep_blank_values: flag indicating whether blank values in
          percent-encoded queries should be treated as blank strings. A
          true value indicates that blanks should be retained as blank
          strings. The default false value indicates that blank values
          are to be ignored and treated as if they were  not included.
  
      encoding and errors: specify how to decode percent-encoded sequences
          into Unicode characters, as accepted by the bytes.decode() method.
  
      fields_limit: maximum number of fields parsed or an exception
          is raised. None means no limit and is the default.
      """
      if fields_limit:
          pairs = FIELDS_MATCH.split(qs, fields_limit)
          if len(pairs) > fields_limit:
              raise TooManyFieldsSent(
                  'The number of GET/POST parameters exceeded '
                  'settings.DATA_UPLOAD_MAX_NUMBER_FIELDS.'
              )
      else:
          pairs = FIELDS_MATCH.split(qs)
      r = []
      for name_value in pairs:
          if not name_value:
              continue
          nv = name_value.split(str('='), 1)
          if len(nv) != 2:
              # Handle case of a control-name with no equal sign
              if keep_blank_values:
                  nv.append('')
              else:
                  continue
          if len(nv[1]) or keep_blank_values:
              name = nv[0].replace('+', ' ')
              name = unquote(name, encoding=encoding, errors=errors)
              value = nv[1].replace('+', ' ')
              value = unquote(value, encoding=encoding, errors=errors)
              r.append((name, value))
      return r
  