How to write lambda with no return and no arguments

Asked Feb 26 '19 at 12:15

Active Feb 26 '19 at 12:22

Viewed 4,259 times

I want to pass a function/lambda to a method and then call it in python 2.7:

def foo(f):
    f()

I tried many ways but didnt find the correct syntax. For example this

foo(lambda: print("hallo"))

results in

    foo(lambda: print("hallo"))
                    ^
SyntaxError: invalid syntax

I know that this works:

foo(lambda x: None)

But I dont know how to make the lambda actually do something and at the same time return None

Related: A suitable 'do nothing' lambda expression in python?, though the lambdas in the answer just do nothing :(

edited Feb 26 '19 at 12:17

asked Feb 26 '19 at 12:15

which version of python are you on? this works fine on python 3.6 – Nullman Feb 26 '19 at 12:16
@Nullman 2.7 sorry, will add that to the question – 463035818_is_not_an_ai Feb 26 '19 at 12:17
3

`print` is a statement in python 2 and thus can't be used in a lambda. – Aran-Fey Feb 26 '19 at 12:17
@Aran-Fey I want to lambda to execute a statement, this is not possible? – 463035818_is_not_an_ai Feb 26 '19 at 12:17
@Aran-Fey anyhow `print` was just an example, consider setting the value of a global variable as a different example – 463035818_is_not_an_ai Feb 26 '19 at 12:18
You can't do that in a lambda, no. (Well, you *can*, but you really shouldn't.) – Aran-Fey Feb 26 '19 at 12:19
@Aran-Fey when I shouldnt then what should i do instead? – 463035818_is_not_an_ai Feb 26 '19 at 12:20
Use a real function instead of a lambda. – Aran-Fey Feb 26 '19 at 12:20
@Aran-Fey [this](https://stackoverflow.com/a/21035557/4117728) answer claims that a lambda **is** just a function, so i though i was on the right track. My goal is just to write it inline together with the call to `foo` instead of having to define a function. Anyhow, with the dupe my problem is solved, I will try to be more pythonic later :P – 463035818_is_not_an_ai Feb 26 '19 at 12:23

0 Answers0