secondary seeking optimisation (precomputation)

Author: arekbulski

kaitaistruct.py

@@ -65,6 +65,7 @@ class KaitaiStream(object):
     def __init__(self, io):
         self._io = io
         self.align_to_byte()
+        self.precompute_size()
 
     def __enter__(self):
         return self
@@ -95,21 +96,17 @@ def pos(self):
         return self._io.tell()
 
     def size(self):
-        if hasattr(self, 'size_cached'):
-            return self.size_cached
+        # Further optimisation: make `size()` into `size`, requires compiler coop.
+        return self.size_cached
+
+    def precompute_size(self):
         # Python has no internal File object API function to get
-        # current file / StringIO size, thus we use the following
-        # trick.
+        # current file / StringIO size, thus we use the following trick.
         io = self._io
-        # Remember our current position
         cur_pos = io.tell()
-        # Seek to the end of the File object
-        # Remember position, which is equal to the full length
         full_size = io.seek(0, SEEK_END)
-        # Seek back to the current position
         io.seek(cur_pos)
         self.size_cached = full_size
-        return full_size
 
     # ========================================================================
     # Integer numbers