Add conditional string encoding based on urllib3 major version

src/requests/compat.py

@@ -10,6 +10,18 @@
 import importlib
 import sys
 
+# -------
+# urllib3
+# -------
+from urllib3 import __version__ as urllib3_version
+
+# Detect which major version of urllib3 is being used.
+try:
+    is_urllib3_2 = int(urllib3_version.split(".")[0]) == 2
+except (TypeError, AttributeError):
+    # If we can't discern a version, prefer old functionality.
+    is_urllib3_2 = False
+
 # -------------------
 # Character Detection
 # -------------------

src/requests/utils.py

@@ -38,6 +38,7 @@
     getproxies,
     getproxies_environment,
     integer_types,
+    is_urllib3_2,
 )
 from .compat import parse_http_list as _parse_list_header
 from .compat import (
@@ -136,7 +137,9 @@ def super_len(o):
     total_length = None
     current_position = 0
 
-    if isinstance(o, str):
+    if is_urllib3_2 and isinstance(o, str):
+        # urllib3 2.x treats all strings as utf-8 instead
+        # of latin-1 (iso-8859-1) like http.client.
         o = o.encode("utf-8")
 
     if hasattr(o, "__len__"):