This method should be a function in context.py

1 files changed, 31 insertions, 0 deletions

diff --git a/coverage/context.py b/coverage/context.py
index 25be98c5..22c0e531 100644
--- a/coverage/context.py
+++ b/coverage/context.py
@@ -3,6 +3,37 @@
 
 """Determine contexts for coverage.py"""
 
+
+def combine_context_switchers(context_switchers):
+    """Create a single context switcher from multiple switchers.
+
+    `context_switchers` is a list of functions that take a frame as an
+    argument and return a string to use as the new context label.
+
+    Returns a function that composites `context_switchers` functions, or None
+    if `context_switchers` is an empty list.
+
+    When invoked, the combined switcher calls `context_switchers` one-by-one
+    until a string is returned.  The combined switcher returns None if all
+    `context_switchers` return None.
+    """
+    if not context_switchers:
+        return None
+
+    if len(context_switchers) == 1:
+        return context_switchers[0]
+
+    def should_start_context(frame):
+        """The combiner for multiple context switchers."""
+        for switcher in context_switchers:
+            new_context = switcher(frame)
+            if new_context is not None:
+                return new_context
+        return None
+
+    return should_start_context
+
+
 def should_start_context_test_function(frame):
     """Is this frame calling a test_* function?"""
     if frame.f_code.co_name.startswith("test"):