Issue 7402: Improve reduce() example in the python idioms how-to.

rhettinger · rhettinger · commit 099cfed120d2 · 2010-10-31T22:00:50.000Z
diff --git a/Doc/howto/doanddont.rst b/Doc/howto/doanddont.rst
@@ -244,24 +244,22 @@ Compare::
 More useful functions in :mod:`os.path`: :func:`basename`,  :func:`dirname` and
 :func:`splitext`.
 
-There are also many useful built-in functions people seem not to be aware of for
-some reason: :func:`min` and :func:`max` can find the minimum/maximum of any
-sequence with comparable semantics, for example, yet many people write their own
-:func:`max`/:func:`min`. Another highly useful function is
-:func:`functools.reduce`.  A classical use of :func:`reduce` is something like
-::
-
-   import sys, operator, functools
-   nums = list(map(float, sys.argv[1:]))
-   print(functools.reduce(operator.add, nums) / len(nums))
-
-This cute little script prints the average of all numbers given on the command
-line. The :func:`reduce` adds up all the numbers, and the rest is just some
-pre- and postprocessing.
-
-On the same note, note that :func:`float` and :func:`int` accept arguments of
-type string, and so are suited to parsing --- assuming you are ready to deal
-with the :exc:`ValueError` they raise.
+There are also many useful built-in functions people seem not to be aware of
+for some reason: :func:`min` and :func:`max` can find the minimum/maximum of
+any sequence with comparable semantics, for example, yet many people write
+their own :func:`max`/:func:`min`. Another highly useful function is
+:func:`functools.reduce` which can be used to repeatly apply a binary
+operation to a sequence, reducing it to a single value.  For example, compute
+a factorial with a series of multiply operations::
+
+   >>> n = 4
+   >>> import operator, functools
+   >>> functools.reduce(operator.mul, range(1, n+1))
+   24
+
+When it comes to parsing numbers, note that :func:`float`, :func:`int` and
+:func:`long` all accept string arguments and will reject ill-formed strings
+by raising an :exc:`ValueError`.
 
 
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