python/build/verify: move code to feed_file()

python/build/verify.py

 import hashlib
 
+def feed_file(h, f):
+    """Feed data read from an open file into the hashlib instance."""
+
+    while True:
+        data = f.read(65536)
+        if len(data) == 0:
+            # end of file
+            break
+        h.update(data)
+
+def feed_file_path(h, path):
+    """Feed data read from a file (to be opened by this function) into the hashlib instance."""
+
+    with open(path, 'rb') as f:
+        feed_file(h, f)
+
 def file_md5(path):
     """Calculate the MD5 checksum of a file and return it in hexadecimal notation."""
 
-    with open(path, 'rb') as f:
-        m = hashlib.md5()
-        while True:
-            data = f.read(65536)
-            if len(data) == 0:
-                # end of file
-                return m.hexdigest()
-            m.update(data)
+    h = hashlib.md5()
+    feed_file_path(h, path)
+    return h.hexdigest()