Bash-like pipes in Python

[Steven D'Aprano]

There's a powerful technique used in shell-scripting languages like bash:
pipes. The output of one function is piped in to become the input to the
next function.

According to Martin Fowler, this was also used extensively in Smalltalk:

http://martinfowler.com/articles/collection-pipeline/

and can also be done in Ruby, using method chaining.

Here is a way to do functional-programming-like pipelines to collect and
transform values from an iterable:

https://code.activestate.com/recipes/580625-collection-pipeline-in-python/

For instance, we can take a string, extract all the digits, convert them to
ints, and finally multiply the digits to give a final result:

py> from operator import mul
py> "abcd12345xyz" | Filter(str.isdigit) | Map(int) | Reduce(mul)
120


(For the definitions of Filter, Map and Reduce, see the code at the
ActiveState recipe, linked above). In my opinion, this is much nicer
looking that the standard Python `filter`, `map` and `reduce`:

py> reduce(mul, map(int, filter(str.isdigit, "abcd12345xyz")))
120

as this requires the operations to be written in the opposite order to the
order that they are applied.



-- 
Steven