Python feature request : operator for function composition

Kay Schluehr kay.schluehr at gmx.net
Sun Feb 3 06:09:26 CET 2008


As you know, there is no operator for function composition in Python.
When you have two functions F and G and  want to express the
composition F o G you have to create a new closure

lambda *args, **kwd: F (G (*args, **kwd))

or you write a composition in functional style

compose( F, G )

None of these solutions is particular terse.

Proposal
-------------
I want to propose overloading the logical __and__ operator i.e. '&'
for functions s.t. F & G means "compose(F,G)". This suggestion is non-
conflicting since & is not used as an operator in combination with
function objects yet: given a function object F and an arbitrary
object X the combination F & X raises a TypeError when evaluated.

Alternatives
-----------------
One could use other unused operators like F << G or F * G to write
terse function composition expressions. I' m not sure which one is
best and would use the proposed & if no one presents arguments against
it.



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