Issue #16537: Check whether self.extensions is empty in setup.py.

Patch by Jonathan Hosmer.

Misc/ACKS

@@ -582,6 +582,7 @@ Randall Hopper
 Nadav Horesh
 Alon Horev
 Jan Hosang
+Jonathan Hosmer
 Alan Hourihane
 Ken Howard
 Brad Howes

Misc/NEWS

@@ -205,6 +205,9 @@ Tests
 Build
 -----
 
+- Issue #16537: Check whether self.extensions is empty in setup.py. Patch by
+  Jonathan Hosmer.
+
 - The documentation Makefile no longer automatically downloads Sphinx. Users are
   now required to have Sphinx already installed to build the documentation.
 

setup.py

@@ -250,7 +250,9 @@ class PyBuildExt(build_ext):
 
         build_ext.build_extensions(self)
 
-        longest = max([len(e.name) for e in self.extensions])
+        longest = 0
+        if self.extensions:
+            longest = max([len(e.name) for e in self.extensions])
         if self.failed:
             longest = max(longest, max([len(name) for name in self.failed]))