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Task/Left-factorials/Python/left-factorials.py

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+from itertools import islice
+
+def lfact():
+    yield 0
+    fact, summ, n = 1, 0, 1
+    while 1:
+        fact, summ, n = fact*n, summ + fact, n + 1
+        yield summ
+
+print('first 11:\n  %r' % [lf for i, lf in zip(range(11), lfact())])
+print('20 through 110 (inclusive) by tens:')
+for lf in islice(lfact(), 20, 111, 10):
+    print(lf)
+print('Digits in 1,000 through 10,000 (inclusive) by thousands:\n  %r'
+      % [len(str(lf)) for lf in islice(lfact(), 1000, 10001, 1000)] )