python
diff --git a/Doc/library/urllib.parse.rst b/Doc/library/urllib.parse.rst
@@ -225,6 +225,11 @@ or on combining URL components into a URL string.
    .. versionchanged:: 3.15
       Added the *missing_as_none* parameter.
 
+   .. versionchanged:: 3.16
+      Values for ``url`` and ``scheme`` other than strings, bytes, or ``None``
+      raise :exc:`TypeError` if true or :exc:`DeprecationWarning` if false (to
+      be changed to :exc:`TypeError` in future versions of Python).
+
 .. _WHATWG spec: https://url.spec.whatwg.org/#concept-basic-url-parser
 
 
@@ -320,6 +325,11 @@ or on combining URL components into a URL string.
       query parameter separator. This has been changed to allow only a single
       separator key, with ``&`` as the default separator.
 
+   .. versionchanged:: 3.16
+      Values for ``qs`` and ``separator`` other than strings, bytes, or
+      ``None`` raise :exc:`TypeError` if true or :exc:`DeprecationWarning` if
+      false (to be changed to :exc:`TypeError` in future versions of Python).
+
 
 .. function:: urlunsplit(parts)
               urlunsplit(parts, *, keep_empty)
@@ -379,6 +389,11 @@ or on combining URL components into a URL string.
    .. versionchanged:: 3.15
       Added the *keep_empty* parameter.
 
+   .. versionchanged:: 3.16
+      Items in ``parts`` other than strings, bytes, or ``None`` raise
+      :exc:`TypeError` if true or :exc:`DeprecationWarning` if false (to be
+      changed to :exc:`TypeError` in future versions of Python).
+
 
 .. function:: urljoin(base, url, allow_fragments=True)
 
@@ -422,6 +437,11 @@ or on combining URL components into a URL string.
 
       Behavior updated to match the semantics defined in :rfc:`3986`.
 
+   .. versionchanged:: 3.16
+      Values for ``base`` and ``url`` other than strings, bytes, or ``None``
+      raise :exc:`TypeError` if true or :exc:`DeprecationWarning` if false (to
+      be changed to :exc:`TypeError` in future versions of Python).
+
 
 .. function:: urldefrag(url, *, missing_as_none=False)
 
@@ -452,6 +472,11 @@ or on combining URL components into a URL string.
    .. versionchanged:: 3.15
       Added the *missing_as_none* parameter.
 
+   .. versionchanged:: 3.16
+      Values other than other than strings, bytes, or ``None`` raise
+      :exc:`TypeError` if true or :exc:`DeprecationWarning` if false (to be
+      changed to :exc:`TypeError` in future versions of Python).
+
 .. function:: unwrap(url)
 
    Extract the url from a wrapped URL (that is, a string formatted as

@@ -680,6 +680,14 @@ New deprecations
     open them one by one instead.
     (Contributed by Serhiy Storchaka in :gh:`152638`.)
 
+* :mod:`urllib`:
+
+  * Providing anything but a string, bytes object, or ``None`` to
+    :mod:`urllib.parse` functions expecting strings or bytes now raises
+    :exc:`DeprecationWarning` if the value tests false, or :exc:`TypeError` if
+    it tests true.
+    (Contributed by Jacob Walls in :issue:`19094`.)
+
 .. Add deprecations above alphabetically, not here at the end.
 
 .. include:: ../deprecations/pending-removal-in-3.17.rst

diff --git a/Lib/test/test_urlparse.py b/Lib/test/test_urlparse.py
@@ -1255,6 +1255,12 @@ def test_mixed_types_rejected(self):
         with self.assertRaisesRegex(TypeError, "Cannot mix str"):
             urllib.parse.urljoin(b"http://python.org", "http://python.org")
 
+    def test_non_string_true_values_rejected(self):
+        # True values raise informative TypeErrors
+        msg = "Expected a string, bytes, or None: got <class "
+        with self.assertRaisesRegex(TypeError, msg):
+            urllib.parse.urlsplit(1, b'http')
+
     def _check_result_type(self, str_type, str_args):
         bytes_type = str_type._encoded_counterpart
         self.assertIs(bytes_type._decoded_counterpart, str_type)
@@ -1992,6 +1998,23 @@ def test_to_bytes_deprecation(self):
         self.assertEqual(str(cm.warning),
                          'urllib.parse.to_bytes() is deprecated as of 3.8')
 
+    def test_falsey_deprecation(self):
+        cases = [
+            (urllib.parse.urljoin, ['http://www.python.org', []]),
+            (urllib.parse.urljoin, [[], b'docs']),
+            (urllib.parse.urlparse, [b'www.python.org', {}]),
+            (urllib.parse.urlparse, [{}, '']),
+            (urllib.parse.urlsplit, [0, b'http']),
+            (urllib.parse.urlsplit, [b'http://www.python.org', 0]),
+            (urllib.parse.urldefrag, [{}]),
+            (urllib.parse.urlunparse, [[None, b'www.python.org', (), (), (), ()]]),
+            (urllib.parse.urlunsplit, [['http', 0, '', '', '']]),
+        ]
+        for func, args in cases:
+            with self.subTest(callable=func.__name__, args=args):
+                with self.assertWarnsRegex(DeprecationWarning, "false values"):
+                    func(*args)
+
 
 def str_encode(s):
     if s is None:

diff --git a/Lib/urllib/parse.py b/Lib/urllib/parse.py
@@ -131,6 +131,13 @@ def _coerce_args(*args):
             else:
                 if isinstance(arg, str) != str_input:
                     raise TypeError("Cannot mix str and non-str arguments")
+            if not hasattr(arg, "decode") and str_input is False:
+                raise TypeError(f"Expected a string, bytes, or None: got {type(arg)}")
+        elif arg is not None and not isinstance(arg, str) and not hasattr(arg, "decode"):
+            warnings.warn(
+                f"Providing false values other than empty strings, bytes, or"
+                f"None to urllib.parse is deprecated: got {type(arg)}",
+                DeprecationWarning, stacklevel=3)
     if str_input is None:
         for arg in args:
             if arg is not None:
@@ -697,12 +704,12 @@ def _urlunsplit(scheme, netloc, url, query, fragment):
 def urljoin(base, url, allow_fragments=True):
     """Join a base URL and a possibly relative URL to form an absolute
     interpretation of the latter."""
+    base, url, _coerce_result = _coerce_args(base, url)
     if not base:
-        return url
+        return _coerce_result(url)
     if not url:
-        return base
+        return _coerce_result(base)
 
-    base, url, _coerce_result = _coerce_args(base, url)
     bscheme, bnetloc, bpath, bquery, bfragment = \
             _urlsplit(base, None, allow_fragments)
     scheme, netloc, path, query, fragment = \

diff --git a/Misc/NEWS.d/next/Library/2021-06-11-20-00-16.bpo-19094.rMRoIL.rst b/Misc/NEWS.d/next/Library/2021-06-11-20-00-16.bpo-19094.rMRoIL.rst
@@ -0,0 +1,4 @@
+Providing values other than other than strings, bytes, or ``None`` to
+:mod:`urllib.parse` functions expecting strings or bytes now raises
+:exc:`TypeError` if true or :exc:`DeprecationWarning` if false (to be
+changed to :exc:`TypeError` in future versions of Python).