depgen.py: consume iterators at C speed.

mkhelper/depgen.py

@@ -44,7 +44,7 @@
 import os
 import sys
 
-from depgen import map23, open23, zip_longest23
+from depgen import exhaust, map23, open23, zip_longest23
 
 
 class ArgumentParser(argparse.ArgumentParser):
@@ -542,8 +542,7 @@ def debug_callback(line, msg):
         )
 
         if parser:
-            for _ in parser.parse(in_stream, in_stream.name):
-                pass
+            exhaust(parser.parse(in_stream, in_stream.name))
 
         not in_stream_close or in_stream.close()
 

mkhelper/depgen/__init__.py

@@ -51,6 +51,20 @@ def map23(foo, iterable):
         return list(map(foo, iterable))
 
 
+if hasattr(sys, "implementation") and sys.implementation.name == "cpython":
+    # see https://docs.python.org/3/library/itertools.html#itertools-recipes
+    import collections
+
+    def exhaust(it):
+        return collections.deque(it, maxlen=0)
+
+else:
+
+    def exhaust(it):
+        for _ in it:
+            pass
+
+
 def file_in_dir(f, d):
     if d:
         return os.path.abspath(f).startswith(os.path.abspath(d) + os.path.sep)