Simplify interleave.

cytoolz/itertoolz.pxd

@@ -36,9 +36,8 @@ cdef object c_merge_sorted(object seqs, object key=*)
 
 cdef class interleave:
     cdef list iters
-    cdef list newiters
     cdef Py_ssize_t i
-    cdef Py_ssize_t n
+    cdef Py_ssize_t active
 
 
 cdef class _unique_key:

cytoolz/itertoolz.pyx

@@ -328,54 +328,46 @@ cdef class interleave:
     Returns a lazy iterator
     """
     def __cinit__(self, seqs):
-        self.iters = [iter(seq) for seq in seqs]
-        self.newiters = []
+        self.iters = list(map(iter, seqs))
         self.i = 0
-        self.n = PyList_GET_SIZE(self.iters)
+        self.active = PyList_GET_SIZE(self.iters)
 
     def __iter__(self):
         return self
 
     def __next__(self):
-        # This implementation is similar to what is done in `toolz` in that we
-        # construct a new list of iterators, `self.newiters`, when a value is
-        # successfully retrieved from an iterator from `self.iters`.
+        cdef object itrobj, val
+        cdef list iters
         cdef PyObject *obj
-        cdef object val
+        cdef Py_ssize_t _len
 
-        if self.i == self.n:
-            self.n = PyList_GET_SIZE(self.newiters)
-            self.i = 0
-            if self.n == 0:
-                raise StopIteration
-            self.iters = self.newiters
-            self.newiters = []
-        val = <object>PyList_GET_ITEM(self.iters, self.i)
+        iters = self.iters
+        _len = PyList_GET_SIZE(iters)
+
+        itrobj = <object>PyList_GET_ITEM(iters, self.i)
         self.i += 1
-        obj = PtrIter_Next(val)
+        if self.i == _len:
+            self.i = 0
+        obj = PtrIter_Next(itrobj)
 
-        # TODO: optimization opportunity.  Previously, it was possible to
-        # continue on given exceptions, `self.pass_exceptions`, which is
-        # why this code is structured this way.  Time to clean up?
         while obj is NULL:
+            # Check if error occurred
             obj = PyErr_Occurred()
             if obj is not NULL:
+                # Iterator raised an exception
                 val = <object>obj
                 PyErr_Clear()
                 raise val
 
-            if self.i == self.n:
-                self.n = PyList_GET_SIZE(self.newiters)
-                self.i = 0
-                if self.n == 0:
-                    raise StopIteration
-                self.iters = self.newiters
-                self.newiters = []
-            val = <object>PyList_GET_ITEM(self.iters, self.i)
-            self.i += 1
-            obj = PtrIter_Next(val)
+            self.active = max(self.active - 1, 0)
+            if self.active == 0:
+                raise StopIteration
 
-        PyList_Append(self.newiters, val)
+            itrobj = <object>PyList_GET_ITEM(iters, self.i)
+            self.i += 1
+            if self.i == _len:
+                self.i = 0
+            obj = PtrIter_Next(itrobj)
         val = <object>obj
         Py_XDECREF(obj)
         return val