diff --git a/news/40711960-12d9-4e58-8322-21e5975a804e.trivial.rst b/news/40711960-12d9-4e58-8322-21e5975a804e.trivial.rst
new file mode 100644
index 000000000..e69de29bb
diff --git a/setup.py b/setup.py
index 66820387b..a413c5f67 100644
--- a/setup.py
+++ b/setup.py
@@ -1,6 +1,3 @@
-# The following comment should be removed at some point in the future.
-# mypy: disallow-untyped-defs=False
-
 import os
 import sys
 
@@ -8,6 +5,7 @@ from setuptools import find_packages, setup
 
 
 def read(rel_path):
+    # type: (str) -> str
     here = os.path.abspath(os.path.dirname(__file__))
     # intentionally *not* adding an encoding option to open, See:
     #   https://github.com/pypa/virtualenv/issues/201#issuecomment-3145690
@@ -16,6 +14,7 @@ def read(rel_path):
 
 
 def get_version(rel_path):
+    # type: (str) -> str
     for line in read(rel_path).splitlines():
         if line.startswith('__version__'):
             # __version__ = "0.9"
diff --git a/src/pip/_internal/cli/parser.py b/src/pip/_internal/cli/parser.py
index 8fd3d2d6b..16523c5a1 100644
--- a/src/pip/_internal/cli/parser.py
+++ b/src/pip/_internal/cli/parser.py
@@ -1,15 +1,12 @@
 """Base option parser setup"""
 
-# The following comment should be removed at some point in the future.
-# mypy: disallow-untyped-defs=False
-
 import logging
 import optparse
 import shutil
 import sys
 import textwrap
 from contextlib import suppress
-from typing import Any
+from typing import Any, Dict, Iterator, List, Tuple
 
 from pip._internal.cli.status_codes import UNKNOWN_ERROR
 from pip._internal.configuration import Configuration, ConfigurationError
@@ -22,6 +19,7 @@ class PrettyHelpFormatter(optparse.IndentedHelpFormatter):
     """A prettier/less verbose help formatter for optparse."""
 
     def __init__(self, *args, **kwargs):
+        # type: (*Any, **Any) -> None
         # help position must be aligned with __init__.parseopts.description
         kwargs["max_help_position"] = 30
         kwargs["indent_increment"] = 1
@@ -29,9 +27,11 @@ class PrettyHelpFormatter(optparse.IndentedHelpFormatter):
         super().__init__(*args, **kwargs)
 
     def format_option_strings(self, option):
+        # type: (optparse.Option) -> str
         return self._format_option_strings(option)
 
     def _format_option_strings(self, option, mvarfmt=" <{}>", optsep=", "):
+        # type: (optparse.Option, str, str) -> str
         """
         Return a comma-separated list of option strings and metavars.
 
@@ -49,17 +49,20 @@ class PrettyHelpFormatter(optparse.IndentedHelpFormatter):
             opts.insert(1, optsep)
 
         if option.takes_value():
+            assert option.dest is not None
             metavar = option.metavar or option.dest.lower()
             opts.append(mvarfmt.format(metavar.lower()))
 
         return "".join(opts)
 
     def format_heading(self, heading):
+        # type: (str) -> str
         if heading == "Options":
             return ""
         return heading + ":\n"
 
     def format_usage(self, usage):
+        # type: (str) -> str
         """
         Ensure there is only one newline between usage and the first heading
         if there is no description.
@@ -68,6 +71,7 @@ class PrettyHelpFormatter(optparse.IndentedHelpFormatter):
         return msg
 
     def format_description(self, description):
+        # type: (str) -> str
         # leave full control over description to us
         if description:
             if hasattr(self.parser, "main"):
@@ -86,6 +90,7 @@ class PrettyHelpFormatter(optparse.IndentedHelpFormatter):
             return ""
 
     def format_epilog(self, epilog):
+        # type: (str) -> str
         # leave full control over epilog to us
         if epilog:
             return epilog
@@ -93,6 +98,7 @@ class PrettyHelpFormatter(optparse.IndentedHelpFormatter):
             return ""
 
     def indent_lines(self, text, indent):
+        # type: (str, str) -> str
         new_lines = [indent + line for line in text.split("\n")]
         return "\n".join(new_lines)
 
@@ -107,9 +113,12 @@ class UpdatingDefaultsHelpFormatter(PrettyHelpFormatter):
     """
 
     def expand_default(self, option):
+        # type: (optparse.Option) -> str
         default_values = None
         if self.parser is not None:
+            assert isinstance(self.parser, ConfigOptionParser)
             self.parser._update_defaults(self.parser.defaults)
+            assert option.dest is not None
             default_values = self.parser.defaults.get(option.dest)
         help_text = super().expand_default(option)
 
@@ -129,6 +138,7 @@ class UpdatingDefaultsHelpFormatter(PrettyHelpFormatter):
 
 class CustomOptionParser(optparse.OptionParser):
     def insert_option_group(self, idx, *args, **kwargs):
+        # type: (int, Any, Any) -> optparse.OptionGroup
         """Insert an OptionGroup at a given position."""
         group = self.add_option_group(*args, **kwargs)
 
@@ -139,6 +149,7 @@ class CustomOptionParser(optparse.OptionParser):
 
     @property
     def option_list_all(self):
+        # type: () -> List[optparse.Option]
         """Get a list of all options, including those in option groups."""
         res = self.option_list[:]
         for i in self.option_groups:
@@ -166,6 +177,7 @@ class ConfigOptionParser(CustomOptionParser):
         super().__init__(*args, **kwargs)
 
     def check_default(self, option, key, val):
+        # type: (optparse.Option, str, Any) -> Any
         try:
             return option.check_value(key, val)
         except optparse.OptionValueError as exc:
@@ -173,11 +185,14 @@ class ConfigOptionParser(CustomOptionParser):
             sys.exit(3)
 
     def _get_ordered_configuration_items(self):
+        # type: () -> Iterator[Tuple[str, Any]]
         # Configuration gives keys in an unordered manner. Order them.
         override_order = ["global", self.name, ":env:"]
 
         # Pool the options into different groups
-        section_items = {name: [] for name in override_order}
+        section_items = {
+            name: [] for name in override_order
+        }  # type: Dict[str, List[Tuple[str, Any]]]
         for section_key, val in self.config.items():
             # ignore empty values
             if not val:
@@ -197,6 +212,7 @@ class ConfigOptionParser(CustomOptionParser):
                 yield key, val
 
     def _update_defaults(self, defaults):
+        # type: (Dict[str, Any]) -> Dict[str, Any]
         """Updates the given defaults with values from the config files and
         the environ. Does a little special handling for certain types of
         options (lists)."""
@@ -215,6 +231,8 @@ class ConfigOptionParser(CustomOptionParser):
             if option is None:
                 continue
 
+            assert option.dest is not None
+
             if option.action in ("store_true", "store_false"):
                 try:
                     val = strtobool(val)
@@ -240,6 +258,7 @@ class ConfigOptionParser(CustomOptionParser):
                 val = val.split()
                 val = [self.check_default(option, key, v) for v in val]
             elif option.action == "callback":
+                assert option.callback is not None
                 late_eval.add(option.dest)
                 opt_str = option.get_opt_string()
                 val = option.convert_value(opt_str, val)
@@ -258,6 +277,7 @@ class ConfigOptionParser(CustomOptionParser):
         return defaults
 
     def get_default_values(self):
+        # type: () -> optparse.Values
         """Overriding to make updating the defaults after instantiation of
         the option parser possible, _update_defaults() does the dirty work."""
         if not self.process_default_values:
@@ -272,6 +292,7 @@ class ConfigOptionParser(CustomOptionParser):
 
         defaults = self._update_defaults(self.defaults.copy())  # ours
         for option in self._get_all_options():
+            assert option.dest is not None
             default = defaults.get(option.dest)
             if isinstance(default, str):
                 opt_str = option.get_opt_string()
@@ -279,5 +300,6 @@ class ConfigOptionParser(CustomOptionParser):
         return optparse.Values(defaults)
 
     def error(self, msg):
+        # type: (str) -> None
         self.print_usage(sys.stderr)
         self.exit(UNKNOWN_ERROR, f"{msg}\n")
diff --git a/src/pip/_internal/network/auth.py b/src/pip/_internal/network/auth.py
index cad22a02c..bd54a5cba 100644
--- a/src/pip/_internal/network/auth.py
+++ b/src/pip/_internal/network/auth.py
@@ -37,7 +37,7 @@ except Exception as exc:
 
 
 def get_keyring_auth(url, username):
-    # type: (str, str) -> Optional[AuthInfo]
+    # type: (Optional[str], Optional[str]) -> Optional[AuthInfo]
     """Return the tuple auth for a given url from keyring."""
     global keyring
     if not url or not keyring:
diff --git a/src/pip/_internal/network/session.py b/src/pip/_internal/network/session.py
index 423922a00..b42d06bc3 100644
--- a/src/pip/_internal/network/session.py
+++ b/src/pip/_internal/network/session.py
@@ -2,8 +2,15 @@
 network request configuration and behavior.
 """
 
-# The following comment should be removed at some point in the future.
-# mypy: disallow-untyped-defs=False
+# When mypy runs on Windows the call to distro.linux_distribution() is skipped
+# resulting in the failure:
+#
+#     error: unused 'type: ignore' comment
+#
+# If the upstream module adds typing, this comment should be removed. See
+# https://github.com/nir0s/distro/pull/269
+#
+# mypy: warn-unused-ignores=False
 
 import email.utils
 import ipaddress
@@ -15,13 +22,14 @@ import platform
 import sys
 import urllib.parse
 import warnings
-from typing import Any, Iterator, List, Optional, Sequence, Tuple, Union
+from typing import Any, Dict, Iterator, List, Mapping, Optional, Sequence, Tuple, Union
 
 from pip._vendor import requests, urllib3
 from pip._vendor.cachecontrol import CacheControlAdapter
 from pip._vendor.requests.adapters import BaseAdapter, HTTPAdapter
-from pip._vendor.requests.models import Response
+from pip._vendor.requests.models import PreparedRequest, Response
 from pip._vendor.requests.structures import CaseInsensitiveDict
+from pip._vendor.urllib3.connectionpool import ConnectionPool
 from pip._vendor.urllib3.exceptions import InsecureRequestWarning
 
 from pip import __version__
@@ -89,6 +97,7 @@ def looks_like_ci():
 
 
 def user_agent():
+    # type: () -> str
     """
     Return a string representing the user agent.
     """
@@ -98,15 +107,14 @@ def user_agent():
         "implementation": {
             "name": platform.python_implementation(),
         },
-    }
+    }  # type: Dict[str, Any]
 
     if data["implementation"]["name"] == 'CPython':
         data["implementation"]["version"] = platform.python_version()
     elif data["implementation"]["name"] == 'PyPy':
-        if sys.pypy_version_info.releaselevel == 'final':
-            pypy_version_info = sys.pypy_version_info[:3]
-        else:
-            pypy_version_info = sys.pypy_version_info
+        pypy_version_info = sys.pypy_version_info  # type: ignore
+        if pypy_version_info.releaselevel == 'final':
+            pypy_version_info = pypy_version_info[:3]
         data["implementation"]["version"] = ".".join(
             [str(x) for x in pypy_version_info]
         )
@@ -119,9 +127,12 @@ def user_agent():
 
     if sys.platform.startswith("linux"):
         from pip._vendor import distro
+
+        # https://github.com/nir0s/distro/pull/269
+        linux_distribution = distro.linux_distribution()  # type: ignore
         distro_infos = dict(filter(
             lambda x: x[1],
-            zip(["name", "version", "id"], distro.linux_distribution()),
+            zip(["name", "version", "id"], linux_distribution),
         ))
         libc = dict(filter(
             lambda x: x[1],
@@ -170,8 +181,16 @@ def user_agent():
 
 class LocalFSAdapter(BaseAdapter):
 
-    def send(self, request, stream=None, timeout=None, verify=None, cert=None,
-             proxies=None):
+    def send(
+        self,
+        request,  # type: PreparedRequest
+        stream=False,  # type: bool
+        timeout=None,  # type: Optional[Union[float, Tuple[float, float]]]
+        verify=True,  # type: Union[bool, str]
+        cert=None,  # type: Optional[Union[str, Tuple[str, str]]]
+        proxies=None,  # type:Optional[Mapping[str, str]]
+    ):
+        # type: (...) -> Response
         pathname = url_to_path(request.url)
 
         resp = Response()
@@ -198,18 +217,33 @@ class LocalFSAdapter(BaseAdapter):
         return resp
 
     def close(self):
+        # type: () -> None
         pass
 
 
 class InsecureHTTPAdapter(HTTPAdapter):
 
-    def cert_verify(self, conn, url, verify, cert):
+    def cert_verify(
+        self,
+        conn,  # type: ConnectionPool
+        url,  # type: str
+        verify,  # type: Union[bool, str]
+        cert,  # type: Optional[Union[str, Tuple[str, str]]]
+    ):
+        # type: (...) -> None
         super().cert_verify(conn=conn, url=url, verify=False, cert=cert)
 
 
 class InsecureCacheControlAdapter(CacheControlAdapter):
 
-    def cert_verify(self, conn, url, verify, cert):
+    def cert_verify(
+        self,
+        conn,  # type: ConnectionPool
+        url,  # type: str
+        verify,  # type: Union[bool, str]
+        cert,  # type: Optional[Union[str, Tuple[str, str]]]
+    ):
+        # type: (...) -> None
         super().cert_verify(conn=conn, url=url, verify=False, cert=cert)
 
 
@@ -407,6 +441,7 @@ class PipSession(requests.Session):
         return False
 
     def request(self, method, url, *args, **kwargs):
+        # type: (str, str, *Any, **Any) -> Response
         # Allow setting a default timeout on a session
         kwargs.setdefault("timeout", self.timeout)
 
diff --git a/src/pip/_internal/resolution/legacy/resolver.py b/src/pip/_internal/resolution/legacy/resolver.py
index c37b396e2..17de7f09a 100644
--- a/src/pip/_internal/resolution/legacy/resolver.py
+++ b/src/pip/_internal/resolution/legacy/resolver.py
@@ -12,13 +12,12 @@ for sub-dependencies
 
 # The following comment should be removed at some point in the future.
 # mypy: strict-optional=False
-# mypy: disallow-untyped-defs=False
 
 import logging
 import sys
 from collections import defaultdict
 from itertools import chain
-from typing import DefaultDict, List, Optional, Set, Tuple
+from typing import DefaultDict, Iterable, List, Optional, Set, Tuple
 
 from pip._vendor.packaging import specifiers
 from pip._vendor.pkg_resources import Distribution
@@ -388,6 +387,7 @@ class Resolver(BaseResolver):
         more_reqs = []  # type: List[InstallRequirement]
 
         def add_req(subreq, extras_requested):
+            # type: (Distribution, Iterable[str]) -> None
             sub_install_req = self._make_install_req(
                 str(subreq),
                 req_to_install,
@@ -447,6 +447,7 @@ class Resolver(BaseResolver):
         ordered_reqs = set()  # type: Set[InstallRequirement]
 
         def schedule(req):
+            # type: (InstallRequirement) -> None
             if req.satisfied_by or req in ordered_reqs:
                 return
             if req.constraint:
diff --git a/src/pip/_internal/utils/compat.py b/src/pip/_internal/utils/compat.py
index 069e3091d..0cb1c4697 100644
--- a/src/pip/_internal/utils/compat.py
+++ b/src/pip/_internal/utils/compat.py
@@ -1,9 +1,6 @@
 """Stuff that differs in different Python versions and platform
 distributions."""
 
-# The following comment should be removed at some point in the future.
-# mypy: disallow-untyped-defs=False
-
 import logging
 import os
 import sys
diff --git a/src/pip/_internal/utils/deprecation.py b/src/pip/_internal/utils/deprecation.py
index 3d52e179a..b62b3fb65 100644
--- a/src/pip/_internal/utils/deprecation.py
+++ b/src/pip/_internal/utils/deprecation.py
@@ -2,12 +2,9 @@
 A module that implements tooling to enable easy warnings about deprecations.
 """
 
-# The following comment should be removed at some point in the future.
-# mypy: disallow-untyped-defs=False
-
 import logging
 import warnings
-from typing import Any, Optional
+from typing import Any, Optional, TextIO, Type, Union
 
 from pip._vendor.packaging.version import parse
 
@@ -24,7 +21,15 @@ _original_showwarning = None  # type: Any
 
 
 # Warnings <-> Logging Integration
-def _showwarning(message, category, filename, lineno, file=None, line=None):
+def _showwarning(
+    message,  # type: Union[Warning, str]
+    category,  # type: Type[Warning]
+    filename,  # type: str
+    lineno,  # type: int
+    file=None,  # type: Optional[TextIO]
+    line=None,  # type: Optional[str]
+):
+    # type: (...) -> None
     if file is not None:
         if _original_showwarning is not None:
             _original_showwarning(message, category, filename, lineno, file, line)
diff --git a/src/pip/_internal/utils/logging.py b/src/pip/_internal/utils/logging.py
index ce78416ec..70b86cc0e 100644
--- a/src/pip/_internal/utils/logging.py
+++ b/src/pip/_internal/utils/logging.py
@@ -1,6 +1,3 @@
-# The following comment should be removed at some point in the future.
-# mypy: disallow-untyped-defs=False
-
 import contextlib
 import errno
 import logging
@@ -8,7 +5,7 @@ import logging.handlers
 import os
 import sys
 from logging import Filter, getLogger
-from typing import Any
+from typing import IO, Any, Callable, Iterator, Optional, TextIO, Type, cast
 
 from pip._internal.utils.compat import WINDOWS
 from pip._internal.utils.deprecation import DEPRECATION_MSG_PREFIX
@@ -46,15 +43,17 @@ if WINDOWS:
     # https://bugs.python.org/issue19612
     # https://bugs.python.org/issue30418
     def _is_broken_pipe_error(exc_class, exc):
+        # type: (Type[BaseException], BaseException) -> bool
         """See the docstring for non-Windows below."""
         return (exc_class is BrokenPipeError) or (
-            exc_class is OSError and exc.errno in (errno.EINVAL, errno.EPIPE)
+            isinstance(exc, OSError) and exc.errno in (errno.EINVAL, errno.EPIPE)
         )
 
 
 else:
     # Then we are in the non-Windows case.
     def _is_broken_pipe_error(exc_class, exc):
+        # type: (Type[BaseException], BaseException) -> bool
         """
         Return whether an exception is a broken pipe error.
 
@@ -67,6 +66,7 @@ else:
 
 @contextlib.contextmanager
 def indent_log(num=2):
+    # type: (int) -> Iterator[None]
     """
     A context manager which will cause the log output to be indented for any
     log messages emitted inside it.
@@ -81,6 +81,7 @@ def indent_log(num=2):
 
 
 def get_indentation():
+    # type: () -> int
     return getattr(_log_state, "indentation", 0)
 
 
@@ -104,6 +105,7 @@ class IndentingFormatter(logging.Formatter):
         super().__init__(*args, **kwargs)
 
     def get_message_start(self, formatted, levelno):
+        # type: (str, int) -> str
         """
         Return the start of the formatted log message (not counting the
         prefix to add to each line).
@@ -120,6 +122,7 @@ class IndentingFormatter(logging.Formatter):
         return "ERROR: "
 
     def format(self, record):
+        # type: (logging.LogRecord) -> str
         """
         Calls the standard formatter, but will indent all of the log message
         lines by our current indentation level.
@@ -137,7 +140,9 @@ class IndentingFormatter(logging.Formatter):
 
 
 def _color_wrap(*colors):
+    # type: (*str) -> Callable[[str], str]
     def wrapped(inp):
+        # type: (str) -> str
         return "".join(list(colors) + [inp, colorama.Style.RESET_ALL])
 
     return wrapped
@@ -156,6 +161,7 @@ class ColorizedStreamHandler(logging.StreamHandler):
         COLORS = []
 
     def __init__(self, stream=None, no_color=None):
+        # type: (Optional[TextIO], bool) -> None
         super().__init__(stream)
         self._no_color = no_color
 
@@ -163,16 +169,19 @@ class ColorizedStreamHandler(logging.StreamHandler):
             self.stream = colorama.AnsiToWin32(self.stream)
 
     def _using_stdout(self):
+        # type: () -> bool
         """
         Return whether the handler is using sys.stdout.
         """
         if WINDOWS and colorama:
             # Then self.stream is an AnsiToWin32 object.
-            return self.stream.wrapped is sys.stdout
+            stream = cast(colorama.AnsiToWin32, self.stream)
+            return stream.wrapped is sys.stdout
 
         return self.stream is sys.stdout
 
     def should_color(self):
+        # type: () -> bool
         # Don't colorize things if we do not have colorama or if told not to
         if not colorama or self._no_color:
             return False
@@ -195,6 +204,7 @@ class ColorizedStreamHandler(logging.StreamHandler):
         return False
 
     def format(self, record):
+        # type: (logging.LogRecord) -> str
         msg = logging.StreamHandler.format(self, record)
 
         if self.should_color():
@@ -207,12 +217,18 @@ class ColorizedStreamHandler(logging.StreamHandler):
 
     # The logging module says handleError() can be customized.
     def handleError(self, record):
+        # type: (logging.LogRecord) -> None
         exc_class, exc = sys.exc_info()[:2]
         # If a broken pipe occurred while calling write() or flush() on the
         # stdout stream in logging's Handler.emit(), then raise our special
         # exception so we can handle it in main() instead of logging the
         # broken pipe error and continuing.
-        if exc_class and self._using_stdout() and _is_broken_pipe_error(exc_class, exc):
+        if (
+            exc_class
+            and exc
+            and self._using_stdout()
+            and _is_broken_pipe_error(exc_class, exc)
+        ):
             raise BrokenStdoutLoggingError()
 
         return super().handleError(record)
@@ -220,15 +236,18 @@ class ColorizedStreamHandler(logging.StreamHandler):
 
 class BetterRotatingFileHandler(logging.handlers.RotatingFileHandler):
     def _open(self):
+        # type: () -> IO[Any]
         ensure_dir(os.path.dirname(self.baseFilename))
         return logging.handlers.RotatingFileHandler._open(self)
 
 
 class MaxLevelFilter(Filter):
     def __init__(self, level):
+        # type: (int) -> None
         self.level = level
 
     def filter(self, record):
+        # type: (logging.LogRecord) -> bool
         return record.levelno < self.level
 
 
@@ -239,12 +258,14 @@ class ExcludeLoggerFilter(Filter):
     """
 
     def filter(self, record):
+        # type: (logging.LogRecord) -> bool
         # The base Filter class allows only records from a logger (or its
         # children).
         return not super().filter(record)
 
 
 def setup_logging(verbosity, no_color, user_log_file):
+    # type: (int, bool, Optional[str]) -> int
     """Configures and sets up all of the logging
 
     Returns the requested logging level, as its integer value.
diff --git a/src/pip/_internal/utils/misc.py b/src/pip/_internal/utils/misc.py
index 4b1fecc93..e41a138a3 100644
--- a/src/pip/_internal/utils/misc.py
+++ b/src/pip/_internal/utils/misc.py
@@ -1,6 +1,5 @@
 # The following comment should be removed at some point in the future.
 # mypy: strict-optional=False
-# mypy: disallow-untyped-defs=False
 
 import contextlib
 import errno
@@ -16,16 +15,21 @@ import sys
 import urllib.parse
 from io import StringIO
 from itertools import filterfalse, tee, zip_longest
+from types import TracebackType
 from typing import (
     Any,
     AnyStr,
+    BinaryIO,
     Callable,
     Container,
+    ContextManager,
     Iterable,
     Iterator,
     List,
     Optional,
+    TextIO,
     Tuple,
+    Type,
     TypeVar,
     cast,
 )
@@ -64,8 +68,10 @@ __all__ = [
 
 logger = logging.getLogger(__name__)
 
-VersionInfo = Tuple[int, int, int]
 T = TypeVar("T")
+ExcInfo = Tuple[Type[BaseException], BaseException, TracebackType]
+VersionInfo = Tuple[int, int, int]
+NetlocTuple = Tuple[str, Tuple[Optional[str], Optional[str]]]
 
 
 def get_pip_version():
@@ -132,6 +138,7 @@ def rmtree(dir, ignore_errors=False):
 
 
 def rmtree_errorhandler(func, path, exc_info):
+    # type: (Callable[..., Any], str, ExcInfo) -> None
     """On Windows, the files in .svn are read-only, so when rmtree() tries to
     remove them, an exception is thrown.  We catch that here, remove the
     read-only attribute, and hopefully continue without problems."""
@@ -279,6 +286,7 @@ def is_installable_dir(path):
 
 
 def read_chunks(file, size=io.DEFAULT_BUFFER_SIZE):
+    # type: (BinaryIO, int) -> Iterator[bytes]
     """Yield pieces of data from a file-like object until EOF."""
     while True:
         chunk = file.read(size)
@@ -491,19 +499,24 @@ def write_output(msg, *args):
 
 
 class StreamWrapper(StringIO):
+    orig_stream = None  # type: TextIO
+
     @classmethod
     def from_stream(cls, orig_stream):
+        # type: (TextIO) -> StreamWrapper
         cls.orig_stream = orig_stream
         return cls()
 
     # compileall.compile_dir() needs stdout.encoding to print to stdout
+    # https://github.com/python/mypy/issues/4125
     @property
-    def encoding(self):
+    def encoding(self):  # type: ignore
         return self.orig_stream.encoding
 
 
 @contextlib.contextmanager
 def captured_output(stream_name):
+    # type: (str) -> Iterator[StreamWrapper]
     """Return a context manager used by captured_stdout/stdin/stderr
     that temporarily replaces the sys stream *stream_name* with a StringIO.
 
@@ -518,6 +531,7 @@ def captured_output(stream_name):
 
 
 def captured_stdout():
+    # type: () -> ContextManager[StreamWrapper]
     """Capture the output of sys.stdout:
 
        with captured_stdout() as stdout:
@@ -530,6 +544,7 @@ def captured_stdout():
 
 
 def captured_stderr():
+    # type: () -> ContextManager[StreamWrapper]
     """
     See captured_stdout().
     """
@@ -538,6 +553,7 @@ def captured_stderr():
 
 # Simulates an enum
 def enum(*sequential, **named):
+    # type: (*Any, **Any) -> Type[Any]
     enums = dict(zip(sequential, range(len(sequential))), **named)
     reverse = {value: key for key, value in enums.items()}
     enums["reverse_mapping"] = reverse
@@ -579,6 +595,7 @@ def parse_netloc(netloc):
 
 
 def split_auth_from_netloc(netloc):
+    # type: (str) -> NetlocTuple
     """
     Parse out and remove the auth information from a netloc.
 
@@ -591,17 +608,20 @@ def split_auth_from_netloc(netloc):
     # behaves if more than one @ is present (which can be checked using
     # the password attribute of urlsplit()'s return value).
     auth, netloc = netloc.rsplit("@", 1)
+    pw = None  # type: Optional[str]
     if ":" in auth:
         # Split from the left because that's how urllib.parse.urlsplit()
         # behaves if more than one : is present (which again can be checked
         # using the password attribute of the return value)
-        user_pass = auth.split(":", 1)
+        user, pw = auth.split(":", 1)
     else:
-        user_pass = auth, None
+        user, pw = auth, None
 
-    user_pass = tuple(None if x is None else urllib.parse.unquote(x) for x in user_pass)
+    user = urllib.parse.unquote(user)
+    if pw is not None:
+        pw = urllib.parse.unquote(pw)
 
-    return netloc, user_pass
+    return netloc, (user, pw)
 
 
 def redact_netloc(netloc):
@@ -628,6 +648,7 @@ def redact_netloc(netloc):
 
 
 def _transform_url(url, transform_netloc):
+    # type: (str, Callable[[str], Tuple[Any, ...]]) -> Tuple[str, NetlocTuple]
     """Transform and replace netloc in a url.
 
     transform_netloc is a function taking the netloc and returning a
@@ -642,14 +663,16 @@ def _transform_url(url, transform_netloc):
     # stripped url
     url_pieces = (purl.scheme, netloc_tuple[0], purl.path, purl.query, purl.fragment)
     surl = urllib.parse.urlunsplit(url_pieces)
-    return surl, netloc_tuple
+    return surl, cast("NetlocTuple", netloc_tuple)
 
 
 def _get_netloc(netloc):
+    # type: (str) -> NetlocTuple
     return split_auth_from_netloc(netloc)
 
 
 def _redact_netloc(netloc):
+    # type: (str) -> Tuple[str,]
     return (redact_netloc(netloc),)
 
 
@@ -765,6 +788,7 @@ def hash_file(path, blocksize=1 << 20):
 
 
 def is_wheel_installed():
+    # type: () -> bool
     """
     Return whether the wheel package is installed.
     """
diff --git a/src/pip/_internal/utils/models.py b/src/pip/_internal/utils/models.py
index daf065825..0e02bc7a5 100644
--- a/src/pip/_internal/utils/models.py
+++ b/src/pip/_internal/utils/models.py
@@ -1,9 +1,8 @@
 """Utilities for defining models
 """
-# The following comment should be removed at some point in the future.
-# mypy: disallow-untyped-defs=False
 
 import operator
+from typing import Any, Callable, Type
 
 
 class KeyBasedCompareMixin:
@@ -12,28 +11,36 @@ class KeyBasedCompareMixin:
     __slots__ = ["_compare_key", "_defining_class"]
 
     def __init__(self, key, defining_class):
+        # type: (Any, Type[KeyBasedCompareMixin]) -> None
         self._compare_key = key
         self._defining_class = defining_class
 
     def __hash__(self):
+        # type: () -> int
         return hash(self._compare_key)
 
     def __lt__(self, other):
+        # type: (Any) -> bool
         return self._compare(other, operator.__lt__)
 
     def __le__(self, other):
+        # type: (Any) -> bool
         return self._compare(other, operator.__le__)
 
     def __gt__(self, other):
+        # type: (Any) -> bool
         return self._compare(other, operator.__gt__)
 
     def __ge__(self, other):
+        # type: (Any) -> bool
         return self._compare(other, operator.__ge__)
 
     def __eq__(self, other):
+        # type: (Any) -> bool
         return self._compare(other, operator.__eq__)
 
     def _compare(self, other, method):
+        # type: (Any, Callable[[Any, Any], bool]) -> bool
         if not isinstance(other, self._defining_class):
             return NotImplemented
 
diff --git a/tools/tox_pip.py b/tools/tox_pip.py
index 5996dade6..fe7621342 100644
--- a/tools/tox_pip.py
+++ b/tools/tox_pip.py
@@ -1,17 +1,16 @@
-# The following comment should be removed at some point in the future.
-# mypy: disallow-untyped-defs=False
-
 import os
 import shutil
 import subprocess
 import sys
 from glob import glob
+from typing import List
 
 VIRTUAL_ENV = os.environ['VIRTUAL_ENV']
 TOX_PIP_DIR = os.path.join(VIRTUAL_ENV, 'pip')
 
 
 def pip(args):
+    # type: (List[str]) -> None
     # First things first, get a recent (stable) version of pip.
     if not os.path.exists(TOX_PIP_DIR):
         subprocess.check_call([sys.executable, '-m', 'pip',
@@ -20,8 +19,8 @@ def pip(args):
                                'pip'])
         shutil.rmtree(glob(os.path.join(TOX_PIP_DIR, 'pip-*.dist-info'))[0])
     # And use that version.
-    pypath = os.environ.get('PYTHONPATH')
-    pypath = pypath.split(os.pathsep) if pypath is not None else []
+    pypath_env = os.environ.get('PYTHONPATH')
+    pypath = pypath_env.split(os.pathsep) if pypath_env is not None else []
     pypath.insert(0, TOX_PIP_DIR)
     os.environ['PYTHONPATH'] = os.pathsep.join(pypath)
     subprocess.check_call([sys.executable, '-m', 'pip'] + args)