optimise calls to slice()

CHANGES.rst

@@ -9,6 +9,8 @@ Latest
 Features added
 --------------
 
+* Calls to ``slice()`` are translated to a straight C-API call.
+
 * Taking a ``char*`` from a temporary Python string object is safer
   in more cases and can be done inside of non-trivial expressions,
   including arguments of a function call.  A compile time error

Cython/Compiler/Optimize.py

@@ -1327,6 +1327,24 @@ class EarlyReplaceBuiltinCalls(Visitor.EnvTransform):
             return pos_args[0]
         return node
 
+    def _handle_simple_function_slice(self, node, pos_args):
+        arg_count = len(pos_args)
+        start = step = None
+        if arg_count == 1:
+            stop, = pos_args
+        elif arg_count == 2:
+            start, stop = pos_args
+        elif arg_count == 3:
+            start, stop, step = pos_args
+        else:
+            self._error_wrong_arg_count('slice', node, pos_args)
+            return node
+        return ExprNodes.SliceNode(
+            node.pos,
+            start=start or ExprNodes.NoneNode(node.pos),
+            stop=stop,
+            step=step or ExprNodes.NoneNode(node.pos))
+
     class YieldNodeCollector(Visitor.TreeVisitor):
         def __init__(self):
             Visitor.TreeVisitor.__init__(self)

tests/run/builtin_slice.pyx

+# mode: run
+
+def slice1(stop):
+    """
+    >>> list(range(8))
+    [0, 1, 2, 3, 4, 5, 6, 7]
+    >>> list(range(10))[slice1(8)]
+    [0, 1, 2, 3, 4, 5, 6, 7]
+    >>> slice1(1)
+    slice(None, 1, None)
+    >>> slice1(10)
+    slice(None, 10, None)
+    >>> slice1(None)
+    slice(None, None, None)
+    >>> slice1(1) == slice(1)
+    True
+    >>> slice1(None) == slice(None)
+    True
+    """
+    return slice(stop)
+
+
+def slice1_const():
+    """
+    >>> slice1_const() == slice(12)
+    True
+    """
+    return slice(12)
+
+
+def slice2(start, stop):
+    """
+    >>> list(range(2, 8))
+    [2, 3, 4, 5, 6, 7]
+    >>> list(range(10))[slice2(2, 8)]
+    [2, 3, 4, 5, 6, 7]
+    >>> slice2(1, 10)
+    slice(1, 10, None)
+    >>> slice2(None, 10)
+    slice(None, 10, None)
+    >>> slice2(4, None)
+    slice(4, None, None)
+    """
+    return slice(start, stop)
+
+
+def slice2_const():
+    """
+    >>> slice2_const() == slice(None, 12)
+    True
+    """
+    return slice(None, 12)
+
+
+def slice3(start, stop, step):
+    """
+    >>> list(range(2, 8, 3))
+    [2, 5]
+    >>> list(range(10))[slice3(2, 8, 3)]
+    [2, 5]
+    >>> slice3(2, None, 3)
+    slice(2, None, 3)
+    >>> slice3(None, 3, 2)
+    slice(None, 3, 2)
+    """
+    return slice(start, stop, step)
+
+
+def slice3_const():
+    """
+    >>> slice3_const() == slice(12, None, 34)
+    True
+    """
+    return slice(12, None, 34)