take_nth, first, second, nth, last, and rest. Faster isiterable.

TODO

@@ -5,12 +5,6 @@ dicttoolz:
 itertoolz:
     merge_sorted
     interleave
-    take_nth
-    first
-    second
-    nth
-    last
-    rest
     get
     mapcat
     sliding_window

coolz/__init__.pxd

@@ -1,11 +1,12 @@
-from .itertoolz cimport (groupby, frequencies, reduceby, take, drop, concat,
-                         concatv, isdistinct, interpose, unique, isiterable,
-                         remove, iterate, accumulate, count, cons)
+from .itertoolz cimport (groupby, frequencies, reduceby,
+                         first, second, nth, take, drop, rest, last,
+                         concat, concatv, isdistinct, interpose, unique,
+                         isiterable, remove, iterate, accumulate,
+                         count, cons, take_nth)
 
 from .functoolz cimport (memoize, c_memoize, curry, c_compose, c_thread_first,
                          c_thread_last, identity, c_pipe, complement, c_juxt,
                          do)
 
 from .dicttoolz cimport (c_merge, c_merge_with, keymap, valmap, assoc,
                          keyfilter, valfilter)
-

coolz/__init__.py

@@ -1,6 +1,8 @@
-from .itertoolz import (groupby, frequencies, reduceby, take, drop, concat,
-                        concatv, isdistinct, interpose, unique, isiterable,
-                        remove, iterate, accumulate, count, cons)
+from .itertoolz import (groupby, frequencies, reduceby,
+                        first, second, nth, take, drop, rest, last,
+                        concat, concatv, isdistinct, interpose, unique,
+                        isiterable, remove, iterate, accumulate,
+                        count, cons, take_nth)
 
 from .functoolz import (memoize, curry, compose, thread_first,
                         thread_last, identity, pipe, complement, juxt, do)

coolz/itertoolz/__init__.pxd

@@ -1,3 +1,4 @@
 from .core cimport (groupby, remove, concat, concatv, frequencies, interpose,
-                    take, drop, unique, reduceby, isiterable, isdistinct,
-                    cons, iterate, accumulate, count)
+                    first, second, nth, take, drop, rest, last, unique,
+                    reduceby, isiterable, isdistinct, cons, iterate,
+                    accumulate, count, take_nth)

coolz/itertoolz/__init__.py

@@ -1,3 +1,4 @@
 from .core import (groupby, remove, concat, concatv, frequencies, interpose,
-                   take, drop, unique, reduceby, isiterable, isdistinct,
-                   cons, iterate, accumulate, count)
+                   first, second, nth, take, drop, rest, last, unique,
+                   reduceby, isiterable, isdistinct, cons, iterate,
+                   accumulate, count, take_nth)

coolz/itertoolz/core.pxd

@@ -38,6 +38,24 @@ cpdef inline object take(int n, object seq)
 cpdef object drop(int n, object seq)
 
 
+cpdef inline object take_nth(int n, object seq)
+
+
+cpdef object first(object seq)
+
+
+cpdef object second(object seq)
+
+
+cpdef object nth(int n, object seq)
+
+
+cpdef object last(object seq)
+
+
+cpdef object rest(object seq)
+
+
 cpdef inline object cons(object el, object seq)
 
 

coolz/itertoolz/core.pyx

@@ -1,6 +1,7 @@
 from cpython.dict cimport PyDict_Contains, PyDict_GetItem, PyDict_New, PyDict_SetItem
 from cpython.list cimport PyList_New, PyList_Append
 from cpython.ref cimport PyObject
+from cpython.sequence cimport PySequence_Check
 from cpython.set cimport PySet_Add, PySet_Contains
 from itertools import chain, islice
 
@@ -202,7 +203,8 @@ cpdef bint isiterable(object x):
         iter(x)
         return True
     except TypeError:
-        return False
+        pass
+    return False
 
 
 cpdef bint isdistinct(object seq):
@@ -259,6 +261,74 @@ cpdef object drop(int n, object seq):
     return iter_seq
 
 
+cpdef inline object take_nth(int n, object seq):
+    """ Every nth item in seq
+
+    >>> list(take_nth(2, [10, 20, 30, 40, 50]))
+    [10, 30, 50]
+    """
+    return islice(seq, 0, None, n)
+
+
+cpdef object first(object seq):
+    """ The first element in a sequence
+
+    >>> first('ABC')
+    'A'
+    """
+    return next(iter(seq))
+
+
+cpdef object second(object seq):
+    """ The second element in a sequence
+
+    >>> second('ABC')
+    'B'
+    """
+    seq = iter(seq)
+    next(seq)
+    return next(seq)
+
+
+cpdef object nth(int n, object seq):
+    """ The nth element in a sequence
+
+    >>> nth(1, 'ABC')
+    'B'
+    """
+    if PySequence_Check(seq):
+        return seq[n]
+    seq = iter(seq)
+    while n > 0:
+        n -= 1
+        next(seq)
+    return next(seq)
+
+
+cpdef object last(object seq):
+    """ The last element in a sequence
+
+    >>> last('ABC')
+    'C'
+    """
+    cdef object val
+    if PySequence_Check(seq):
+        return seq[-1]
+    seq = iter(seq)
+    try:
+        while True:
+            val = next(seq)
+    except StopIteration:
+        pass
+    return val
+
+
+cpdef object rest(object seq):
+    seq = iter(seq)
+    next(seq)
+    return seq
+
+
 cpdef inline object cons(object el, object seq):
     """ Add el to beginning of (possibly infinite) sequence seq.
 

coolz/itertoolz/tests/test_core.py

@@ -4,11 +4,12 @@
 from coolz.itertoolz.core import (remove, groupby,
                                   concat, concatv, unique,
                                   identity, isiterable,
-                                  isdistinct,
-                                  take, drop, interpose,
-                                  cons, frequencies,
+                                  isdistinct, first, second,
+                                  nth, take, drop, interpose,
+                                  rest, last, cons, frequencies,
                                   reduceby, iterate, accumulate,
-                                  count)
+                                  count,
+                                  take_nth)
 
 from toolz.compatibility import range, filter
 from operator import add, mul
@@ -88,45 +89,35 @@ def test_isdistinct():
     assert isdistinct(iter([1, 2, 1])) is False
 
 
-'''
 def test_nth():
     assert nth(2, 'ABCDE') == 'C'
     assert nth(2, iter('ABCDE')) == 'C'
     assert nth(1, (3, 2, 1)) == 2
     assert nth(0, {'foo': 'bar'}) == 'foo'
     assert raises(StopIteration, lambda: nth(10, {10: 'foo'}))
-'''
 
 
-'''
 def test_first():
     assert first('ABCDE') == 'A'
     assert first((3, 2, 1)) == 3
     assert isinstance(first({0: 'zero', 1: 'one'}), int)
-'''
 
 
-'''
 def test_second():
     assert second('ABCDE') == 'B'
     assert second((3, 2, 1)) == 2
     assert isinstance(second({0: 'zero', 1: 'one'}), int)
-'''
 
 
-'''
 def test_last():
     assert last('ABCDE') == 'E'
     assert last((3, 2, 1)) == 1
     assert isinstance(last({0: 'zero', 1: 'one'}), int)
-'''
 
 
-'''
 def test_rest():
     assert list(rest('ABCDE')) == list('BCDE')
     assert list(rest((3, 2, 1))) == list((2, 1))
-'''
 
 
 def test_take():
@@ -139,10 +130,8 @@ def test_drop():
     assert list(drop(1, (3, 2, 1))) == list((2, 1))
 
 
-'''
 def test_take_nth():
     assert list(take_nth(2, 'ABCDE')) == list('ACE')
-'''
 
 
 '''
@@ -193,7 +182,7 @@ def test_concatv():
 
 
 def test_interpose():
-    # assert "a" == first(rest(interpose("a", range(1000000000))))
+    assert "a" == first(rest(interpose("a", range(1000000000))))
     assert "tXaXrXzXaXn" == "".join(interpose("X", "tarzan"))
     assert list(interpose(0, itertools.repeat(1, 4))) == [1, 0, 1, 0, 1, 0, 1]
     assert list(interpose('.', ['a', 'b', 'c'])) == ['a', '.', 'b', '.', 'c']