diff --git a/Doc/library/urllib.parse.rst b/Doc/library/urllib.parse.rst
index f9936288fd42cdc..025893932e82a16 100644
--- a/Doc/library/urllib.parse.rst
+++ b/Doc/library/urllib.parse.rst
@@ -599,7 +599,7 @@ task isn't already covered by the URL parsing functions above.
 .. function:: urlencode(query, doseq=False, safe='', encoding=None, \
                         errors=None, quote_via=quote_plus)
 
-   Convert a mapping object or a sequence of two-element tuples, which may
+   Convert a mapping object or an iterable of two-element iterables, which may
    contain :class:`str` or :class:`bytes` objects, to a percent-encoded ASCII
    text string.  If the resultant string is to be used as a *data* for POST
    operation with the :func:`~urllib.request.urlopen` function, then
@@ -616,13 +616,14 @@ task isn't already covered by the URL parsing functions above.
    and not encode '/' characters.  For maximum control of what is quoted, use
    ``quote`` and specify a value for *safe*.
 
-   When a sequence of two-element tuples is used as the *query*
-   argument, the first element of each tuple is a key and the second is a
-   value. The value element in itself can be a sequence and in that case, if
-   the optional parameter *doseq* is evaluates to ``True``, individual
-   ``key=value`` pairs separated by ``'&'`` are generated for each element of
-   the value sequence for the key.  The order of parameters in the encoded
-   string will match the order of parameter tuples in the sequence.
+   When an iterable of two-element iterables is used as the *query* argument,
+   the first element of each tuple is a key and the second is a value. The
+   value element is interpreted as a string when the *doseq* parameter
+   evaluates to ``False``. When it evaluates to ``True`` and value is an
+   iterable, then individual ``key=value`` pairs separated by ``'&'`` are
+   generated for each element of the value sequence for the key. The order of
+   parameters in the encoded string will match the order of parameter tuples in
+   the sequence.
 
    The *safe*, *encoding*, and *errors* parameters are passed down to
    *quote_via* (the *encoding* and *errors* parameters are only passed
@@ -640,6 +641,9 @@ task isn't already covered by the URL parsing functions above.
    .. versionadded:: 3.5
       *quote_via* parameter.
 
+   .. versionchanged:: 3.8
+      *doseq=True* iterates on generators and iterators.
+
 
 .. seealso::
 
diff --git a/Lib/test/test_urlparse.py b/Lib/test/test_urlparse.py
index d0365ecab72ccb1..d4969fbaaf4d854 100644
--- a/Lib/test/test_urlparse.py
+++ b/Lib/test/test_urlparse.py
@@ -723,10 +723,6 @@ def test_portseparator(self):
         self.assertEqual(urllib.parse.urlparse(b"http://www.python.org:80"),
                 (b'http',b'www.python.org:80',b'',b'',b'',b''))
 
-    def test_usingsys(self):
-        # Issue 3314: sys module is used in the error
-        self.assertRaises(TypeError, urllib.parse.urlencode, "foo")
-
     def test_anyscheme(self):
         # Issue 7904: s3://foo.com/stuff has netloc "foo.com".
         self.assertEqual(urllib.parse.urlparse("s3://foo.com/stuff"),
@@ -902,6 +898,39 @@ def __str__(self):
         result = urllib.parse.urlencode({'a': Trivial()}, True)
         self.assertEqual(result, 'a=trivial')
 
+    def test_urlencode_generators(self):
+        def gen():
+            yield from range(2)
+
+        result = urllib.parse.urlencode({'a': gen()}, True)
+        self.assertEqual(result, 'a=0&a=1')
+
+    def test_urlencode_iterable_of_iterable_pairs(self):
+        def pair(start):
+            yield ['key', range(start, start+2)]
+
+        def elements():
+            for i in [0, 2]:
+                yield from pair(i)
+
+        result = urllib.parse.urlencode(elements(), doseq=True)
+        self.assertEqual(result, 'key=0&key=1&key=2&key=3')
+
+        result = urllib.parse.urlencode(elements(), doseq=False)
+        # str is called on the range, resulting in values like 'range(0, 2)'
+        self.assertEqual(result, 'key=range%280%2C+2%29&key=range%282%2C+4%29')
+
+    def test_urlencode_two_chars(self):
+        """Do not interpret strings of length 2 as key value pair."""
+        self.assertRaises(TypeError, urllib.parse.urlencode, ['ab'], doseq=True)
+        self.assertRaises(TypeError, urllib.parse.urlencode, ['ab'], doseq=False)
+
+    def test_urlencode_sequence_of_non_pairs(self):
+        self.assertRaises(ValueError, urllib.parse.urlencode, [(1,)], doseq=True)
+        self.assertRaises(ValueError, urllib.parse.urlencode, [(1,)], doseq=False)
+        self.assertRaises(ValueError, urllib.parse.urlencode, [(1, 2, 3)], doseq=True)
+        self.assertRaises(ValueError, urllib.parse.urlencode, [(1, 2, 3)], doseq=False)
+
     def test_urlencode_quote_via(self):
         result = urllib.parse.urlencode({'a': 'some value'})
         self.assertEqual(result, "a=some+value")
diff --git a/Lib/urllib/parse.py b/Lib/urllib/parse.py
index dfba704144e9b4b..b83b790fef08fd8 100644
--- a/Lib/urllib/parse.py
+++ b/Lib/urllib/parse.py
@@ -28,7 +28,6 @@
 """
 
 import re
-import sys
 import collections
 import warnings
 
@@ -879,82 +878,61 @@ def quote_from_bytes(bs, safe='/'):
 
 def urlencode(query, doseq=False, safe='', encoding=None, errors=None,
               quote_via=quote_plus):
-    """Encode a dict or sequence of two-element tuples into a URL query string.
+    """Encode a dict or iterable of two-element iterables into a URL query
+    string.
 
-    If any values in the query arg are sequences and doseq is true, each
-    sequence element is converted to a separate parameter.
+    If any values in the query argument are iterables and doseq is true, each
+    iterable element is converted to a separate parameter.
 
-    If the query arg is a sequence of two-element tuples, the order of the
-    parameters in the output will match the order of parameters in the
-    input.
+    If the query argument is an iterable, the order of the parameters in the
+    output will match the order of parameters in the input.
 
-    The components of a query arg may each be either a string or a bytes type.
+    The components of a query argument may each be either a string or a bytes
+    type.
 
     The safe, encoding, and errors parameters are passed down to the function
     specified by quote_via (encoding and errors only if a component is a str).
     """
-
     if hasattr(query, "items"):
         query = query.items()
-    else:
-        # It's a bother at times that strings and string-like objects are
-        # sequences.
-        try:
-            # non-sequence items should not work with len()
-            # non-empty strings will fail this
-            if len(query) and not isinstance(query[0], tuple):
-                raise TypeError
-            # Zero-length sequences of all types will get here and succeed,
-            # but that's a minor nit.  Since the original implementation
-            # allowed empty dicts that type of behavior probably should be
-            # preserved for consistency
-        except TypeError:
-            ty, va, tb = sys.exc_info()
-            raise TypeError("not a valid non-string sequence "
-                            "or mapping object").with_traceback(tb)
 
     l = []
-    if not doseq:
-        for k, v in query:
-            if isinstance(k, bytes):
-                k = quote_via(k, safe)
-            else:
-                k = quote_via(str(k), safe, encoding, errors)
+    for pair in query:
+        # Evaluate then check, in case pair is an iterator.
+        k, v = pair
+        if isinstance(pair, (str, bytes)):
+            # 'ab' would unpack as k='a' and v='b'.
+            raise TypeError("not a valid non-string sequence or mapping object")
+
+        if isinstance(k, bytes):
+            k = quote_via(k, safe)
+        else:
+            k = quote_via(str(k), safe, encoding, errors)
 
-            if isinstance(v, bytes):
-                v = quote_via(v, safe)
-            else:
-                v = quote_via(str(v), safe, encoding, errors)
+        if isinstance(v, bytes):
+            v = quote_via(v, safe)
             l.append(k + '=' + v)
-    else:
-        for k, v in query:
-            if isinstance(k, bytes):
-                k = quote_via(k, safe)
-            else:
-                k = quote_via(str(k), safe, encoding, errors)
-
-            if isinstance(v, bytes):
-                v = quote_via(v, safe)
-                l.append(k + '=' + v)
-            elif isinstance(v, str):
-                v = quote_via(v, safe, encoding, errors)
+        elif isinstance(v, str):
+            v = quote_via(v, safe, encoding, errors)
+            l.append(k + '=' + v)
+        elif not doseq:
+            v = quote_via(str(v), safe, encoding, errors)
+            l.append(k + '=' + v)
+        else:  # doseq=True
+            try:
+                iter(v)
+            except TypeError:
+                # not a sequence
+                v = quote_via(str(v), safe, encoding, errors)
                 l.append(k + '=' + v)
             else:
-                try:
-                    # Is this a sufficient test for sequence-ness?
-                    x = len(v)
-                except TypeError:
-                    # not a sequence
-                    v = quote_via(str(v), safe, encoding, errors)
-                    l.append(k + '=' + v)
-                else:
-                    # loop over the sequence
-                    for elt in v:
-                        if isinstance(elt, bytes):
-                            elt = quote_via(elt, safe)
-                        else:
-                            elt = quote_via(str(elt), safe, encoding, errors)
-                        l.append(k + '=' + elt)
+                # loop over the sequence
+                for elt in v:
+                    if isinstance(elt, bytes):
+                        elt = quote_via(elt, safe)
+                    else:
+                        elt = quote_via(str(elt), safe, encoding, errors)
+                    l.append(k + '=' + elt)
     return '&'.join(l)
 
 
diff --git a/Misc/NEWS.d/next/Library/2017-11-02-20-47-19.bpo-31706.wA-rWj.rst b/Misc/NEWS.d/next/Library/2017-11-02-20-47-19.bpo-31706.wA-rWj.rst
new file mode 100644
index 000000000000000..115e1eed7b1a596
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2017-11-02-20-47-19.bpo-31706.wA-rWj.rst
@@ -0,0 +1,3 @@
+Made ``urllib.parse.urlencode`` iterate on any iterable object when the
+``doseq`` parameter is ``True``. Each pair in the iterable can now be an
+iterable (while only ``tuple`` was accepted before).