X-Git-Url: https://wannabe.guru.org/gitweb/?a=blobdiff_plain;f=iter_utils.py;h=69f58226aada7b718f6e938e2d635a74fea5ba53;hb=562a15c6397610cf93646d9530005eb4a0d6e6f8;hp=00c4221b26201d7c0a3a1b5bfee938d00371d914;hpb=1172b6778a036431b542fdc89bbfdd13e13b5e8d;p=python_utils.git

diff --git a/iter_utils.py b/iter_utils.py
index 00c4221..69f5822 100644
--- a/iter_utils.py
+++ b/iter_utils.py
@@ -1,12 +1,25 @@
 #!/usr/bin/env python3
 
+# © Copyright 2021-2022, Scott Gasch
+
+"""A collection if :class:`Iterator` subclasses that can be composed
+with another iterator and provide extra functionality.  e.g.
+
+    + :class:`PeekingIterator`
+    + :class:`PushbackIterator`
+    + :class:`SamplingIterator`
+
+"""
+
 import random
 from collections.abc import Iterator
 from typing import Any, List, Optional
 
 
 class PeekingIterator(Iterator):
-    """An iterator that lets you peek at the next item on deck.
+    """An iterator that lets you peek() at the next item on deck.
+    Returns None when there is no next item (i.e. when
+    __next__() will produce a StopIteration exception).
 
     >>> p = PeekingIterator(iter(range(3)))
     >>> p.__next__()
@@ -25,6 +38,7 @@ class PeekingIterator(Iterator):
     Traceback (most recent call last):
       ...
     StopIteration
+
     """
 
     def __init__(self, source_iter: Iterator):
@@ -52,11 +66,61 @@ class PeekingIterator(Iterator):
             return None
 
 
+class PushbackIterator(Iterator):
+    """An iterator that allows you to push items back
+    onto the front of the sequence.  e.g.
+
+    >>> i = PushbackIterator(iter(range(3)))
+    >>> i.__next__()
+    0
+    >>> i.push_back(99)
+    >>> i.push_back(98)
+    >>> i.__next__()
+    98
+    >>> i.__next__()
+    99
+    >>> i.__next__()
+    1
+    >>> i.__next__()
+    2
+    >>> i.push_back(100)
+    >>> i.__next__()
+    100
+    >>> i.__next__()
+    Traceback (most recent call last):
+      ...
+    StopIteration
+    """
+
+    def __init__(self, source_iter: Iterator):
+        self.source_iter = source_iter
+        self.pushed_back: List[Any] = []
+
+    def __iter__(self) -> Iterator:
+        return self
+
+    def __next__(self) -> Any:
+        if len(self.pushed_back) > 0:
+            return self.pushed_back.pop()
+        return self.source_iter.__next__()
+
+    def push_back(self, item: Any):
+        self.pushed_back.append(item)
+
+
 class SamplingIterator(Iterator):
     """An iterator that simply echoes what source_iter produces but also
     collects a random sample (of size sample_size) of the stream that can
     be queried at any time.
 
+    .. note::
+        Until sample_size elements have been seen the sample will be
+        less than sample_size elements in length.
+
+    .. note::
+        If sample_size is > len(source_iter) then it will produce a
+        copy of source_iter.
+
     >>> import collections
     >>> import random
 
@@ -89,7 +153,7 @@ class SamplingIterator(Iterator):
         return self
 
     def __next__(self) -> Any:
-        item = self.source_iter.__next__()  # or raise
+        item = self.source_iter.__next__()
         self.stream_length_so_far += 1
 
         # Filling the resovoir