Change measured_files to a set

3 files changed, 8 insertions, 12 deletions

diff --git a/coverage/control.py b/coverage/control.py
index 0918a34e..f7d97cf6 100644
--- a/coverage/control.py
+++ b/coverage/control.py
@@ -683,15 +683,11 @@ class Coverage(object):
         if not morfs:
             morfs = self._data.measured_files()
 
-        # Be sure we have a list.
-        if not isinstance(morfs, (list, tuple)):
+        # Be sure we have a collection.
+        if not isinstance(morfs, (list, tuple, set)):
             morfs = [morfs]
 
-        file_reporters = []
-        for morf in morfs:
-            file_reporter = self._get_file_reporter(morf)
-            file_reporters.append(file_reporter)
-
+        file_reporters = [self._get_file_reporter(morf) for morf in morfs]
         return file_reporters
 
     def report(
diff --git a/coverage/data.py b/coverage/data.py
index f03e90ca..3250196d 100644
--- a/coverage/data.py
+++ b/coverage/data.py
@@ -252,8 +252,8 @@ class CoverageJsonData(object):
         return self._runs
 
     def measured_files(self):
-        """A list of all files that had been measured."""
-        return list(self._arcs or self._lines or {})
+        """A set of all files that had been measured."""
+        return set(self._arcs or self._lines or {})
 
     def __nonzero__(self):
         return bool(self._lines or self._arcs)
diff --git a/coverage/sqldata.py b/coverage/sqldata.py
index 6dde9c2e..b9488557 100644
--- a/coverage/sqldata.py
+++ b/coverage/sqldata.py
@@ -304,7 +304,7 @@ class CoverageSqliteData(SimpleRepr):
         aliases = aliases or PathAliases()
 
         # See what we had already measured, for accurate conflict reporting.
-        this_measured = set(self.measured_files())
+        this_measured = self.measured_files()
 
         # lines
         if other_data._has_lines:
@@ -381,8 +381,8 @@ class CoverageSqliteData(SimpleRepr):
         return bool(self._has_arcs)
 
     def measured_files(self):
-        """A list of all files that had been measured."""
-        return list(self._file_map)
+        """A set of all files that had been measured."""
+        return set(self._file_map)
 
     def file_tracer(self, filename):
         """Get the plugin name of the file tracer for a file.