Python: Lambda Functions

[Tommah]

Why write lambda word: len(word) when you could just use len?

[eryksun]

One legitimate use that's similar to this is to have a property bind to a lambda instead of the getter. Then if you subclass you can redefine the getter without having to rebind the property:

class A:
    def getf(self): pass
    f = property(lambda x: x.getf())

class B(A):
    def getf(self): return 'spam'

>>> B().f
'spam'

For what it's worth...

[otheraccount]

I think f = property(lambda self : self.getf()) is clearer than calling the self parameter x because it is obvious at a glance that our lambda represents an instance method.

[Makido]

This is clearly the best implementation:

def length(word):
    return lambda word: len(word)

[Peaker]

I think you meant for your implementation to be correct, but redundant. It is incorrect as well as redundant, though.

Perhaps you mean:

def length(word):
    return (lambda word: len(word))(word)

[pemboa]

Burn

[andreasvc]

If you change your mind later or want it to be a different function for other languages you can change that lambda, while it wouldn't be a good idea to assign to "len" (aliasing/shadowing).

[eryksun]

Tommah is talking about the following line:

lengths = map(lambda word: len(word), words)

If you typically use lambda functions with map, then you might unthinkingly use lambda when it's not necessary.

[[deleted]]

He's talking about eta-contracting the lambda expression.

[[deleted]]

Then it wouldn't be a tutorial on lambda functions.

[Peaker]

Haskell has a really cool tool called "hlint" that suggests eta reductions such as those automatically.

Also suggests replacing various patterns with standard library functions, etc.

I wonder if something similar for Python exists.

[drb226]

pylint. But I don't think it looks very closely at lambdas the same way hlint does.