Add unpythonic.it.pad: extend iterable to length n with fillvalue

unpythonic/it.py

@@ -19,7 +19,7 @@
            "unpack",
            "tail", "butlast", "butlastn",
            "first", "second", "nth", "last", "lastn",
-           "scons",
+           "scons", "pad",
            "flatten", "flatten1", "flatten_in",
            "iterate", "iterate1",
            "partition",
@@ -462,6 +462,21 @@ def scons(x, iterable):
     """
     return chain((x,), iterable)
 
+def pad(n, fillvalue, iterable):
+    """Pad iterable with copies of fillvalue so its length is at least ``n``.
+
+    Examples::
+
+        assert tuple(pad(5, None, range(3))) == (0, 1, 2, None, None)
+        assert tuple(pad(5, None, ())) == (None, None, None, None, None)
+        assert tuple(pad(5, None, range(6))) == tuple(range(6))
+    """
+    k = 0  # used if iterable is empty
+    for k, x in enumerate(iterable, start=1):
+        yield x
+    for _ in range(k, n):
+        yield fillvalue
+
 def flatten(iterable, pred=None):
     """Recursively remove nested structure from iterable.
 

unpythonic/test/test_it.py

@@ -10,7 +10,7 @@
                  map_longest, mapr_longest, rmap_longest, \
                  zip_longest, zipr_longest, rzip_longest, \
                  first, second, nth, last, lastn, \
-                 scons, tail, butlast, butlastn, \
+                 scons, pad, tail, butlast, butlastn, \
                  flatmap, \
                  take, drop, split_at, \
                  rev, \
@@ -70,6 +70,10 @@ def noneadd(a, b):
     assert tuple(scons(0, range(1, 5))) == tuple(range(5))
     assert tuple(tail(scons("foo", range(5)))) == tuple(range(5))
 
+    assert tuple(pad(5, None, range(3))) == (0, 1, 2, None, None)
+    assert tuple(pad(5, None, ())) == (None, None, None, None, None)
+    assert tuple(pad(5, None, range(6))) == tuple(range(6))
+
     assert tuple(butlast(range(5))) == (0, 1, 2, 3)
     assert tuple(butlastn(3, range(5))) == (0, 1)