Add "extend" function to iterative.

Author: domdfcoding

domdf_python_tools/iterative.py

@@ -33,7 +33,20 @@
 import itertools
 import textwrap
 from operator import itemgetter
-from typing import Any, Callable, Generator, Iterable, Iterator, List, Optional, Sequence, Tuple, Type, Union
+from typing import (
+		Any,
+		Callable,
+		Generator,
+		Iterable,
+		Iterator,
+		List,
+		Optional,
+		Sequence,
+		Tuple,
+		Type,
+		TypeVar,
+		Union
+		)
 
 # 3rd party
 from natsort import natsorted, ns  # type: ignore
@@ -53,8 +66,11 @@
 		"natmax",
 		"groupfloats",
 		"ranges_from_iterable",
+		"extend",
 		]
 
+_T = TypeVar("_T")
+
 
 def chunks(l: Sequence[Any], n: int) -> Generator[Any, None, None]:
 	"""
@@ -322,3 +338,22 @@ def ranges_from_iterable(iterable: Iterable[float], step: float = 1) -> Iterable
 
 	for group in groupfloats(iterable, step):
 		yield group[0], group[-1]
+
+
+def extend(sequence: Iterable[_T], minsize: int) -> List[_T]:
+	"""
+	Extend ``sequence`` by repetition until it is at least as long as ``minsize``.
+
+	.. versionadded:: 2.3.0
+
+	:param sequence:
+	:param minsize:
+	"""
+
+	output = list(sequence)
+	cycle = itertools.cycle(output)
+
+	while len(output) < minsize:
+		output.append(next(cycle))
+
+	return output

tests/test_iterative.py

@@ -21,6 +21,7 @@
 		Len,
 		chunks,
 		double_chain,
+		extend,
 		flatten,
 		groupfloats,
 		make_tree,
@@ -220,3 +221,23 @@ def test_ranges_from_iterable():
 
 	expects = [(1, 5), (7, 10)]
 	assert list(ranges_from_iterable([1, 2, 3, 4, 5, 7, 8, 9, 10])) == expects
+
+
+def _extend_param(sequence, expects):
+	return pytest.param(sequence, expects, id=sequence)
+
+
+@pytest.mark.parametrize(
+		"sequence, expects",
+		[
+				_extend_param('a', "aaaa"),
+				_extend_param("ab", "abab"),
+				_extend_param("abc", "abca"),
+				_extend_param("abcd", "abcd"),
+				_extend_param("abcde", "abcde"),
+				pytest.param(('a', 'b', 'c', 'd', 'e'), "abcde", id="tuple"),
+				pytest.param(['a', 'b', 'c', 'd', 'e'], "abcde", id="list"),
+				]
+		)
+def test_extend(sequence, expects):
+	assert ''.join(extend(sequence, 4)) == expects