Update docs.

[python_utils.git] / iter_utils.py

diff --git a/iter_utils.py b/iter_utils.py
index 977cf1df2b7e103f140757a71316339522d6c3ff..69f58226aada7b718f6e938e2d635a74fea5ba53 100644 (file)
--- a/iter_utils.py
+++ b/iter_utils.py
@@ -1,5 +1,16 @@
 #!/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
@@ -7,8 +18,8 @@ from typing import Any, List, Optional
 
 class PeekingIterator(Iterator):
     """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).
+    Returns None when there is no next item (i.e. when
+    __next__() will produce a StopIteration exception).
 
     >>> p = PeekingIterator(iter(range(3)))
     >>> p.__next__()
@@ -27,6 +38,7 @@ class PeekingIterator(Iterator):
     Traceback (most recent call last):
       ...
     StopIteration
+
     """
 
     def __init__(self, source_iter: Iterator):
@@ -54,16 +66,60 @@ 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 that until sample_size elements have been seen the sample will
-    be less than sample_size elements in length.
+    .. note::
+        Until sample_size elements have been seen the sample will be
+        less than sample_size elements in length.
 
-    Note that if sample_size is > len(source_iter) then it will produce
-    a copy of source_iter.
+    .. note::
+        If sample_size is > len(source_iter) then it will produce a
+        copy of source_iter.
 
     >>> import collections
     >>> import random