Small changes to map() and filter():

(1) If a sequence S is shorter than len(S) indicated, don't fail --
just use the shorter size.  (I.e, len(S) is just a hint.)

(2) Implement the special case map(None, S) as list(S) -- it's faster.

diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index 775c318becae69217d677efc68a9c5e1297ded33..63531db2ea6fdad47d4df53f04d15112d21047cf 100644 (file)
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -190,8 +190,6 @@ builtin_filter(self, args)
                int ok;
 
                if ((item = (*sqf->sq_item)(seq, i)) == NULL) {
-                       if (i < len)
-                               goto Fail_1;
                        if (PyErr_ExceptionMatches(PyExc_IndexError)) {
                                PyErr_Clear();
                                break;
@@ -784,6 +782,11 @@ builtin_map(self, args)
        func = PyTuple_GetItem(args, 0);
        n--;
 
+       if (func == Py_None && n == 1) {
+               /* map(None, S) is the same as list(S). */
+               return PySequence_List(PyTuple_GetItem(args, 1));
+       }
+
        if ((seqs = PyMem_NEW(sequence, n)) == NULL) {
                PyErr_NoMemory();
                goto Fail_2;
@@ -820,7 +823,6 @@ builtin_map(self, args)
        if ((result = (PyObject *) PyList_New(len)) == NULL)
                goto Fail_2;
 
-       /* XXX Special case map(None, single_list) could be more efficient */
        for (i = 0; ; ++i) {
                PyObject *alist, *item=NULL, *value;
                int any = 0;
@@ -840,8 +842,6 @@ builtin_map(self, args)
                        else {
                                item = (*sqp->sqf->sq_item)(sqp->seq, i);
                                if (item == NULL) {
-                                       if (i < sqp->len)
-                                               goto Fail_0;
                                        if (PyErr_ExceptionMatches(
                                                PyExc_IndexError))
                                        {
@@ -897,6 +897,9 @@ builtin_map(self, args)
                }
        }
 
+       if (i < len && PyList_SetSlice(result, i, len, NULL) < 0)
+               goto Fail_1;
+
        PyMem_DEL(seqs);
        return result;