`take`: function to select a few items from an iterable

To avoid processing all the items in an iterable, the `take` function
is added in this commit. It realised a limited number (specified at
call time) of items from the iterable given.

1 files changed, 13 insertions, 3 deletions

diff --git a/tests/qc/test_error_collection.py b/tests/qc/test_error_collection.py
index c45803a..f1bd8b9 100644
--- a/tests/qc/test_error_collection.py
+++ b/tests/qc/test_error_collection.py
@@ -1,6 +1,6 @@
 import pytest
 
-from quality_control.parsing import FileType, parse_errors
+from quality_control.parsing import take, FileType, parse_errors
 
 @pytest.mark.slow
 @pytest.mark.parametrize(
@@ -14,8 +14,7 @@ from quality_control.parsing import FileType, parse_errors
       FileType.STANDARD_ERROR, 0),
      ("tests/test_data/standarderror.tsv", FileType.STANDARD_ERROR, 0),
      ("tests/test_data/duplicated_headers_no_data_errors.tsv",
-      FileType.AVERAGE),
-     ))
+      FileType.AVERAGE, 0)))
 def test_parse_errors(filepath, filetype, strains, seek_pos):
     """
     Check that only errors are returned, and that certain properties hold for
@@ -28,3 +27,14 @@ def test_parse_errors(filepath, filetype, strains, seek_pos):
         assert "position" in error
         assert "error" in error and isinstance(error["error"], str)
         assert "message" in error
+
+
+@pytest.mark.parametrize(
+    "sample,num,expected",
+    ((range(0,25), 5, [0, 1, 2, 3, 4]),
+     ([0, 1, 2, 3], 200, [0, 1, 2, 3]),
+     (("he", "is", "a", "lovely", "boy"), 3, ["he", "is", "a"])))
+def test_take(sample, num, expected):
+    taken = take(sample, num)
+    assert len(taken) <= num
+    assert taken == expected