How to pass one function to another in python

Question

I'm relatively new to python and I was wondering if it's possible to pass one function to another. I have some functions that basically do the same think like:

if(#some condition):
  #do something
else:
  #do something else

What I want to do is something like this:

def generic_func(self, x, y):
  if #somecondition:
   #do function x
  else:
   #do function y

def calls_generic_func(self, key, value):
  lambda x: self.list[-1].set(key,value)
  lambda y: self.d.set(key,value)
  self.generic_func(x,y)

Unfortunately this doesn't seem to work as when I call self.generic_fun(x,y) I get an error that says global name x is not defined. Any ideas?

possible duplicate of Passing functions with arguments to another function in Python? — Paul
– Paul, Commented Nov 1, 2014 at 2:23
In calls_generic_func a lambda expression on a line by itself like that is simply thrown away. It does not define x or y, that's possibly why self.generic_func(x,y) fails. fun = lambda x: x*x is equivalent to def fun(x): (new indented line) return x*x Basically lambda lets you write one line functions inline, because def doesn't let you do that (unlike javascript's function() ) — Paul
– Paul, Commented Nov 1, 2014 at 2:29

falsetru · Accepted Answer · 2014-11-01 02:05:34Z

2

x in the following expression is a parameter, not a function (lambda).

lambda x: self.list[-1].set(key,value)

You need to assign the lambda expression to a variable and pass that.

function1 = lambda x: self.list[-1].set(key,value)
function2 = lambda y: self.d.set(key,value)
self.generic_func(function1, function2)

Or you can pass the lambda expression itself:

self.generic_func(lambda x: self.list[-1].set(key,value),
                  lambda y: self.d.set(key,value))

If you meant the functions do not take any parameter, remove them (x, y).

self.generic_func(lambda: self.list[-1].set(key,value),
                  lambda: self.d.set(key,value))

answered Nov 1, 2014 at 2:05

falsetru

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6 Comments

Paul Over a year ago

Do you think something might be wrong with the lambda expressions, seeing as how the left hand parameters x and y are never used in the right hand side for the result? The syntax is allowed, sure. A function is allowed to ignore its parameters. But functionally it is not a good sign.

falsetru Over a year ago

@Paul, It depends on the situation. For example, if caller calls with event object, you can ignore it. (BTW, I added mention about parameter in the answer)

falsetru Over a year ago

@Paul, In Python arguments should match parameters (except arbitrary parameters, keyword parameters)

user3766476 Over a year ago

So when I do it with a lambda function my set command doesn't seem to work correctly. The only thing I'm changing is making is a lambda expression instead of explicitly doing it. Any ideas why that might be happening?

falsetru Over a year ago

@user3766476, Without knowing what the list self.list contain, I can't answer that. Is there set method in the object contains in the list?

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