Add exercise on packing/unpacking with functions

stream.py

@@ -0,0 +1,51 @@
+"""Simulation of random streams of data.
+
+This module defines:
+- a generator object `data` modeling an infinite stream of integers
+- a function `make_finite_stream()` that creates finite streams of data
+
+The probability distribution underlying the integers is Gaussian-like with a
+mean of 42 and a standard deviation of 8. The left tail of the distribution is
+cut off meaning that the streams only produce non-negative numbers. Further,
+one in a hundred random numbers has an increased chance to be an outlier.
+"""
+
+import itertools as _itertools
+import random as _random
+
+
+_random.seed(87)
+
+
+def _infinite_stream():
+    """Internal generator function to simulate an infinite stream of data."""
+    while True:
+        number = max(0, int(_random.gauss(42, 8)))
+        if _random.randint(1, 100) == 1:
+            number *= 2
+        yield number
+
+
+def make_finite_stream(min_=5, max_=15):
+    """Simulate a finite stream of data.
+
+    The returned stream is finite, but the number of elements to be produced
+    by it is still random. This default behavior may be turned off by passing
+    in `min_` and `max_` arguments with `min_ == max_`.
+
+    Args:
+        min_ (optional, int): minimum numbers in the stream; defaults to 5
+        max_ (optional, int): maximum numbers in the stream; defaults to 15
+
+    Returns:
+        finite_stream (generator)
+
+    Raises:
+        ValueError: if max_ < min_
+    """
+    stream = _infinite_stream()
+    n = _random.randint(min_, max_)
+    yield from _itertools.islice(stream, n)
+
+
+data = _infinite_stream()