add DelayedJoin

sisyphus/delayed_ops.py

@@ -180,3 +180,18 @@ def __init__(self, iterable, index_start=0, index_end=-1, step=1):
     def get(self):
         return try_get(self.iterable)[try_get(self.index_start):try_get(self.index_end):try_get(self.step)]
 
+
+class DelayedJoin(DelayedBase):
+
+    def __init__(self, iterable, separator):
+        """
+
+        :param Iterable[DelayedBase|str] iterable:
+        :param str separator:
+        """
+        self.iterable = iterable
+        self.separator = separator
+
+    def get(self):
+        return self.separator.join([try_get(obj) for obj in self.iterable])
+

tests/delayed_ops_unittest.py

@@ -68,6 +68,10 @@ def test_string(self):
         self.check_only_get_eq(a[:-1], 'fooba')
         self.check_only_get_eq(a[1:-1], 'ooba')
 
+    def test_join(self):
+        delayed_join = DelayedJoin([tk.Path("/random/path"), "/foo/bar"], ";")
+        self.check_only_get_eq(delayed_join, "/random/path;/foo/bar")
+
     def test_assertions(self):
         a = Delayed('foo')
         self.assertRaises(AssertionError, lambda: a.function(lambda a, b: a + b, 'bar'))