New submission from David Turner <[EMAIL PROTECTED]>: This is a patch to Tom Lee's AST optimization branch.
Python bytecode includes at least one operation which is not directly accessible from Python code: LIST_APPEND, which pops a value and a list off the stack and appends the value to the list. This is used in generating code for list comprehensions: [x for x in somelist] generates the following code for the body of the loop: ... LOAD_FAST 1#a local is generated to hold the new list LOAD_FAST 2 #the iteration variable, x LIST_APPEND ... Whereas if you were to try to write the comprehension directly, you would get: LOAD_FAST 1 LOAD_ATTR 0 #an index into the constant table: “append” LOAD_FAST 2 CALL_FUNCTION 1 #remove x and the append function from the top of the stack and push the result of the call POP_TOP This is much slower. In part, it’s the cost of doing the attribute lookup each time, which is why it’s common to see code like a = [] ap = a.append for x in …..: ap(x + …) return a But the function call is naturally slower than the simpler LIST_APPEND operation. The attached patch tries to determine statically if a local is all circumstances holds a list, and if so, generates LIST_APPEND whenever user code would call local.append. It’s not perfect — in particular, I could track local types on a more fine-grained level than per-function. But it’s a start. ---------- files: tlee-ast-optimize-appends.diff keywords: patch messages: 75525 nosy: novalis_dt severity: normal status: open title: Patch: optimize code to use LIST_APPEND instead of calling list.append Added file: http://bugs.python.org/file11946/tlee-ast-optimize-appends.diff _______________________________________ Python tracker <[EMAIL PROTECTED]> <http://bugs.python.org/issue4264> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
