Fix flaky Python generator

The existing code checked if a directory existed and if it did, it would
not attempt to create it. However, this proved to be flaky on Mac and Linux.
The check would frequently report the directory as not existing, but the
attempt to create the directory would cause an exception.

src/generator/template.py

@@ -56,16 +56,16 @@ author = "Mike Hamburg" # FUTURE
 for name in args.files:
     _,_,name_suffix = name.rpartition(".")
     template0 = open(name,"r").read()
-    
+
     data = per_map[args.per][args.item]
 
     template = template0
-    
+
     outname = args.o
     guard = args.guard
     if guard is None: guard = outname
     header_guard = "__" + guard.replace(".","_").replace("/","_").upper() + "__"
-    
+
     # Extract doxygenation
     m = re.match(r"^\s*/\*\*([^*]|\*[^/])+\*/[ \t]*\n",template)
     if m:
@@ -73,12 +73,12 @@ for name in args.files:
         doc = re.sub("\\s*\*/","",doc)
         template = template[m.end():]
     else: doc = ""
-    
+
     ns_doc = dedent(doc).strip().rstrip()
     ns_doc = redoc(guard, fillin(ns_doc,data), author)
     ns_code = fillin(template,data)
     ret = ns_doc + "\n"
-    
+
     if outname.endswith(".h") or outname.endswith(".hxx"):
         ns_code = dedent("""\n
             #ifndef %(header_guard)s
@@ -87,11 +87,11 @@ for name in args.files:
             #endif /* %(header_guard)s */
             """) % { "header_guard" : header_guard, "code": ns_code }
     ret += ns_code[1:-1]
-    
-    if not os.path.exists(os.path.dirname(outname)):
+
+    try:
         os.makedirs(os.path.dirname(outname))
+    except OSError as e:
+        if e.errno != 17:  # errno.EEXIST
+            raise
     with open(outname,"w") as f:
         f.write(ret + "\n")
-
-
-