style: kill ersatz if-else ternary operators Although Python supports `X = Y if COND else Z`, this was only introduced in Python 2.5. Since we have to support Python 2.4, it was a very common thing to write instead `X = COND and Y or Z`, which is a bit obscure at a glance. It requires some intricate knowledge of Python to understand how to parse these one-liners. We change instead all of these one-liners to 4-liners. This was executed with the following perlism: find -name "*.py" -exec perl -pi -e 's,(\s*)([\.\w]+) = \(?(\S+)\s+and\s+(\S*)\)?\s+or\s+(\S*)$,$1if $3:\n$1 $2 = $4\n$1else:\n$1 $2 = $5,' {} \; I tweaked the following cases from the automatic Perl output: prev = (parents and parents[0]) or nullid port = (use_ssl and 443 or 80) cwd = (pats and repo.getcwd()) or '' rename = fctx and webutil.renamelink(fctx) or [] ctx = fctx and fctx or ctx self.base = (mapfile and os.path.dirname(mapfile)) or '' I also added some newlines wherever they seemd appropriate for readability There are probably a few ersatz ternary operators still in the code somewhere, lurking away from the power of a simple regex.

--- a/mercurial/dagutil.py	Fri Mar 13 14:20:13 2015 -0400
+++ b/mercurial/dagutil.py	Fri Mar 13 17:00:06 2015 -0400
@@ -88,7 +88,10 @@
     '''generic implementations for DAGs'''
 
     def ancestorset(self, starts, stops=None):
-        stops = stops and set(stops) or set()
+        if stops:
+            stops = set(stops)
+        else:
+            stops = set()
         seen = set()
         pending = list(starts)
         while pending:
@@ -179,7 +182,10 @@
     def ancestorset(self, starts, stops=None):
         rlog = self._revlog
         idx = rlog.index
-        stops = stops and set(stops) or set()
+        if stops:
+            stops = set(stops)
+        else:
+            stops = set()
         seen = set()
         pending = list(starts)
         while pending: