Fix #172: Compute ABI correctly for Python < 3.8.

CHANGES.rst

@@ -34,6 +34,8 @@ Released: Not yet.
 
     - Fixed #169: Removed usage of deprecated imp module in favour of importlib.
 
+    - Fixed #172: Compute ABI correctly for Python < 3.8.
+
 In addition to the above, setup.py was replaced by setup.cfg and pyproject.toml.
 
 0.3.4

distlib/wheel.py

@@ -60,10 +60,18 @@ def _derive_abi():
         parts = ['cp', VER_SUFFIX]
         if sysconfig.get_config_var('Py_DEBUG'):
             parts.append('d')
-        if sysconfig.get_config_var('WITH_PYMALLOC'):
-            parts.append('m')
-        if sysconfig.get_config_var('Py_UNICODE_SIZE') == 4:
-            parts.append('u')
+        if IMP_PREFIX == 'cp':
+            vi = sys.version_info[:2]
+            if vi < (3, 8):
+                wpm = sysconfig.get_config_var('WITH_PYMALLOC')
+                if wpm is None:
+                    wpm = True
+                if wpm:
+                    parts.append('m')
+                if vi < (3, 3):
+                    us = sysconfig.get_config_var('Py_UNICODE_SIZE')
+                    if us == 4 or (us is None and sys.maxunicode == 0x10FFFF):
+                        parts.append('u')
         return ''.join(parts)
     ABI = _derive_abi()
     del _derive_abi