Is it possible to pass functions with arguments to another function in Python?
Say for something like:
def Perform ( function ) :
function
but the functions to be passed will be like:
Action1()
Action2(p)
Action3(p,r)
views:
2291answers:
5
+11
A:
This is what lambda is for:
def Perform(f):
f()
Perform(lambda: Action1())
Perform(lambda: Action2(p))
Perform(lambda: Action3(p, r))
Dave
2009-04-29 18:27:44
-1: lambda -- there's almost always a better way.
S.Lott
2009-04-29 18:38:46
Also out of curiosity, can you please tell me why lambdas are not good for this case?
Joan Venge
2009-04-29 19:19:01
lambdas are one of the best features of good programming languages. unfortunately, Python's implementation is severely limited. in this case, however, they fit perfectly
Javier
2009-04-29 19:23:01
I find that the limited syntax is nearly opaque; they're hard to explain to n00bz. Yes, they do work here, and the confusing features of the syntax are absent. This is -- perhaps -- the only example I've seen of a lambda that's not obscure.
S.Lott
2009-04-29 20:17:19
So that you could retrieve the passed function's result, wouldn't it be better if Perform() called "return f()" rather than just calling f().
mhawke
2009-04-30 01:55:31
+12
A:
Do you mean this?
def perform( fun, *args ):
fun( *args )
def action1( args ):
something
def action2( args ):
something
perform( action1 )
perform( action2, p )
perform( action3, p, r )
S.Lott
2009-04-29 18:28:24
It depends on whether you want the arguments to be evaluated at the call site of Perform or not.
Dave
2009-04-29 18:46:48
+4
A:
You can use the partial function from functools like so.
from functools import partial
def perform(f):
f()
perform(Action1)
perform(partial(Action2, p))
perform(partial(Action3, p, r))
Also works with keywords
perform(partial(Action4, param1=p))
null
2009-04-29 21:23:23
A:
(months later) a tiny real example where lambda is useful, partial not:
say you want various 1-dimensional cross-sections through a 2-dimensional function,
like slices through a row of hills.
quadf( x, f ) takes a 1-d f and calls it for various x.
To call it for vertical cuts at y = -1 0 1 and horizontal cuts at x = -1 0 1,
fx1 = quadf( x, lambda x: f( x, 1 ))
fx0 = quadf( x, lambda x: f( x, 0 ))
fx_1 = quadf( x, lambda x: f( x, -1 ))
fxy = parabola( y, fx_1, fx0, fx1 )
f_1y = quadf( y, lambda y: f( -1, y ))
f0y = quadf( y, lambda y: f( 0, y ))
f1y = quadf( y, lambda y: f( 1, y ))
fyx = parabola( x, f_1y, f0y, f1y )
As far as I know, partial can't do this --
quadf( y, partial( f, x=1 ))
TypeError: f() got multiple values for keyword argument 'x'
(How to add tags numpy, partial, lambda to this ?)
Denis
2009-06-27 15:12:20