update from Atlas repo

iterables/fibo_by_hand.py

@@ -0,0 +1,51 @@
+"""
+Fibonacci generator implemented "by hand" without generator objects
+
+    >>> from itertools import islice
+    >>> list(islice(Fibonacci(), 15))
+    [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377]
+
+"""
+
+
+# BEGIN FIBO_BY_HAND
+class Fibonacci:
+
+    def __iter__(self):
+        return FibonacciGenerator()
+
+
+class FibonacciGenerator:
+
+    def __init__(self):
+        self.a = 0
+        self.b = 1
+
+    def __next__(self):
+        result = self.a
+        self.a, self.b = self.b, self.a + self.b
+        return result
+
+    def __iter__(self):
+        return self
+# END FIBO_BY_HAND
+
+# for comparison, this is the usual implementation of a Fibonacci
+# generator in Python:
+
+
+def fibonacci():
+    a, b = 0, 1
+    while True:
+        yield a
+        a, b = b, a + b
+
+
+if __name__ == '__main__':
+
+    for x, y in zip(Fibonacci(), fibonacci()):
+        assert x == y, '%s != %s' % (x, y)
+        print(x)
+        if x > 10**10:
+            break
+    print('etc...')