add textiter module with head and tail functions

Author: chrissimpkins

lib/fdiff/textiter.py

@@ -0,0 +1,12 @@
+from collections import deque
+from itertools import islice
+
+
+def head(iterable, n):
+    """Returns the first n indices of `iterable` as an iterable."""
+    return islice(iterable, n)
+
+
+def tail(iterable, n):
+    """Returns the last n indices of `iterable` as an iterable."""
+    return iter(deque(iterable, maxlen=n))

tests/test_textiter.py

@@ -0,0 +1,42 @@
+
+
+import pytest
+
+from fdiff.textiter import head, tail
+
+text_list = [
+    "line 1",
+    "line 2",
+    "line 3",
+    "line 4",
+    "line 5"
+]
+
+
+def test_head():
+    head_res = head(text_list, 2)
+    assert len(list(head_res)) == 2
+    for x, line in enumerate(head_res):
+        assert line == text_list[x]
+
+
+def test_head_request_more_than_available():
+    head_res = head(text_list, 6)
+    assert len(list(head_res)) == 5
+    for x, line in enumerate(head_res):
+        assert line == text_list[x]
+
+
+def test_tail():
+    tail_res = tail(text_list, 2)
+    assert len(list(tail_res)) == 2
+    offset = 3
+    for x, line in enumerate(tail_res):
+        assert line == text_list[offset + x]
+
+
+def test_tail_request_more_than_available():
+    tail_res = tail(text_list, 6)
+    assert len(list(tail_res)) == 5
+    for x, line in enumerate(tail_res):
+        assert line == text_list[x]