#!/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__()
Traceback (most recent call last):
...
StopIteration
+
"""
def __init__(self, source_iter: 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
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