added AlreadySeen

CHANGELOG.md

 # v2.14.35
 
+* added AlreadySeen

docs/coding/sequences.rst

@@ -54,6 +54,13 @@ elements matching the callable. If there are, raises ValueError.
 .. autofunction:: satella.coding.sequences.choose_one
 
 
+AlreadySeen
+-----------
+
+.. autoclass:: satella.coding.sequences.AlreadySeen
+    :members:
+
+
 filter_out_nones
 ----------------
 

satella/__init__.py

-__version__ = '2.14.35a1'
+__version__ = '2.14.35a2'

satella/coding/sequences/__init__.py

@@ -4,7 +4,7 @@ from .iterators import infinite_counter, take_n, is_instance, skip_first, zip_sh
     stop_after, iter_dict_of_list, shift, other_sequence_no_longer_than, count, even, \
     odd, n_th, smart_enumerate, smart_zip, unique, ConstruableIterator, walk, length, map_list, \
     is_empty, IteratorListAdapter, enumerate2, to_iterator, ListWrapperIterator, try_close, \
-    f_range, iterate_callable
+    f_range, iterate_callable, AlreadySeen
 from .sequences import is_last, add_next, half_cartesian, group_quantity, Multirun, make_list, \
     infinite_iterator, filter_out_false, filter_out_nones, index_of, index_of_max
 
@@ -16,4 +16,4 @@ __all__ = ['choose', 'choose_one', 'infinite_counter', 'take_n', 'is_instance',
            'make_list', 'RollingArithmeticAverage', 'index_of', 'index_of_max',
            'IteratorListAdapter', 'enumerate2', 'infinite_iterator', 'to_iterator',
            'filter_out_false', 'filter_out_nones', 'ListWrapperIterator', 'try_close',
-           'f_range', 'iterate_callable']
+           'f_range', 'iterate_callable', 'AlreadySeen']

satella/coding/sequences/iterators.py

@@ -5,7 +5,7 @@ import warnings
 
 from ..decorators import for_argument, wraps
 from ..recast_exceptions import rethrow_as, silence_excs
-from ..typing import Iteratable, T, U, Predicate, V
+from ..typing import Iteratable, T, U, Predicate, V, K
 
 
 def iterate_callable(clbl: tp.Callable[[int], V], start_from: int = 0,
@@ -183,6 +183,30 @@ class ConstruableIterator:
         return len(self.entries)
 
 
+class AlreadySeen(tp.Generic[K]):
+    """
+    Class to filter out unique objects
+    """
+    __slots__ = ('set',)
+
+    def __init__(self):
+        self.set = set()
+
+    def is_unique(self, key: K) -> bool:
+        """
+        Has the element been spotted first time?
+
+        Add it to the set.
+
+        :param key: element to check
+        :return: whether the element was seen for the first time
+        """
+        try:
+            return key not in self.set
+        finally:
+            self.set.add(key)
+
+
 def unique(lst: Iteratable) -> tp.Iterator[T]:
     """
     Return each element from lst, but return every element only once.

tests/test_coding/test_sequences.py

@@ -6,12 +6,17 @@ from satella.coding.sequences import choose, choose_one, infinite_counter, take_
     iter_dict_of_list, shift, other_sequence_no_longer_than, count, even, odd, Multirun, n_th, \
     unique, length, map_list, smart_zip, is_empty, make_list, RollingArithmeticAverage, \
     enumerate2, infinite_iterator, to_iterator, filter_out_false, filter_out_nones, \
-    index_of, index_of_max, try_close, f_range, iterate_callable
+    index_of, index_of_max, try_close, f_range, iterate_callable, AlreadySeen
 from satella.coding.predicates import x
 
 
 class TestSequences(unittest.TestCase):
 
+    def test_already_seen(self):
+        as_ = AlreadySeen()
+        self.assertTrue(as_.is_unique(1))
+        self.assertFalse(as_.is_unique(1))
+
     def test_iterate_callable(self):
         a = [1, 2, 3]
         b = lambda i: a[i]