added `IteratorListAdapter`

CHANGELOG.md

@@ -3,3 +3,4 @@
 * added `make_list`
 * fixed typing issue in `choose` and `choose_one`
 * added `RollingArithmeticAverage`
+* added `IteratorListAdapter`

docs/coding/sequences.rst

@@ -11,6 +11,12 @@ Rolling averages
 Standard routines
 =================
 
+IteratorListAdapter
+-------------------
+
+.. autoclass:: satella.coding.sequences.IteratorListAdapter
+    :members:
+
 map_list
 --------
 

satella/__init__.py

-__version__ = '2.11.10_a9'
+__version__ = '2.11.10_a10'

satella/coding/sequences/__init__.py

@@ -2,7 +2,7 @@ from .choose import choose, choose_one
 from .iterators import infinite_counter, take_n, is_instance, skip_first, zip_shifted, \
     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
+    is_empty, IteratorListAdapter
 from .sequences import is_last, add_next, half_cartesian, group_quantity, Multirun, make_list
 from .average import RollingArithmeticAverage
 
@@ -11,4 +11,5 @@ __all__ = ['choose', 'choose_one', 'infinite_counter', 'take_n', 'is_instance',
            'half_cartesian', 'skip_first', 'zip_shifted', 'stop_after', 'group_quantity',
            'iter_dict_of_list', 'shift', 'other_sequence_no_longer_than', 'count', 'n_th',
            'even', 'odd', 'Multirun', 'smart_enumerate', 'unique', 'map_list', 'is_empty',
-           'make_list', 'RollingArithmeticAverage']
+           'make_list', 'RollingArithmeticAverage',
+           'IteratorListAdapter']

satella/coding/sequences/iterators.py

@@ -358,6 +358,58 @@ def n_th(iterator: IteratorOrIterable, n: int = 0) -> T:
         raise IndexError('Iterable was too short')
 
 
+class IteratorListAdapter:
+    """
+    A wrapper around an iterator that enables it to be processed as a list.
+
+    Ie. the generator will now support __contains__, __len__ and __getitem__.
+    If a call to such a method is done, the generator will be unfolded in memory so this
+    might take a ton of memory! You've been warned!
+    
+    :param iterator: 
+    """
+    __slots__ = ('unfolded', 'iterator', 'list', 'pointer')
+
+    def __init__(self, iterator: tp.Iterator):
+        self.iterator = iter(iterator)
+        self.list = None        # type: list
+        self.unfolded = False
+        self.pointer = 0
+
+    def __iter__(self):
+        if self.unfolded:
+            return iter(self.list)
+        else:
+            return self
+
+    @rethrow_as(IndexError, StopIteration)
+    def __next__(self):
+        if self.unfolded:
+            self.pointer += 1
+            return self.list[self.pointer-1]    # throws: IndexError
+        else:
+            return next(self.iterator)
+
+    def __unfold(self):
+        if self.unfolded:
+            return
+        self.list = list(self.iterator)
+        self.unfolded = True
+        self.pointer = 0
+
+    def __getitem__(self, item):
+        self.__unfold()
+        return self.list[item]
+
+    def __contains__(self, item) -> bool:
+        self.__unfold()
+        return item in self.list
+
+    def __len__(self) -> int:
+        self.__unfold()
+        return len(self.list)
+
+
 def is_empty(iterable: IteratorOrIterable) -> bool:
     """
     Checks whether an iterator is empty.

tests/test_coding/test_iterators.py

@@ -2,11 +2,19 @@ import sys
 import unittest
 
 from satella.coding import SelfClosingGenerator, hint_with_length, chain
-from satella.coding.sequences import smart_enumerate, ConstruableIterator, walk
+from satella.coding.sequences import smart_enumerate, ConstruableIterator, walk, \
+    IteratorListAdapter
 
 
 class TestIterators(unittest.TestCase):
 
+    def test_generator_list_adapter(self):
+        gla = IteratorListAdapter(range(10))
+        self.assertEqual(next(gla), 0)
+        self.assertEqual(gla[0], 1)
+        self.assertEqual(len(gla), 9)
+        self.assertEqual(list(gla), list(range(1, 10)))
+
     def test_walk(self):
         a = [[1, 2, 3], 4, 5, 6, [7, 8, 9]]
         b = walk(a, lambda x: x if isinstance(x, list) else None, leaves_only=True)