[Tutor] lambda

[Ajit Deshpande]

Fantastic explanation everyone. Thanks a lot. Looking forward to using
lambda going forward.

~ Ajit Deshpande


On Sat, Mar 19, 2011 at 6:07 PM, Steven D'Aprano <steve at pearwood.info>wrote:

> Ajit Deshpande wrote:
>
>> I am trying to figure out where lambda functions can be useful. Has anyone
>> used them in real world?
>>
>
> Of course. lambdas are especially useful for callback functions, which are
> especially common when doing GUI programming.
>
>
>
>  From my reading so far, I hear people claim that lambda can be a useful
>> replacement for small functions. Most examples  didn't make much sense to
>> me. Why would anyone use a one liner anonymous function, if you never plan
>> to use it elsewhere?
>>
>
> That's precisely the point -- why would you define a non-anonymous function
> that you only use once?
>
> def spam(x):
>    return x + something
>
> register_handler(spam)  # Provide a callback to some part of your app
> # never use spam again
>
>
> is better written as:
>
> register_handler(lambda x: x+something)
>
>
>
>   You would then be implementing the logic directly in
>> the line, isn't it?. Functions are useful if they plan to get called
>> multiple times within your code.
>>
>
> That's often the case, but not necessarily.
>
>
>
>
>  For example:
>>
>> add_one = lambda x: x + 1
>>
>
> This defines a function "add_one". This is equivalent to writing:
>
> def add_one(x):
>    return x+1
>
>
>  In real world, why would I use a lambda for this. I would simply do:
>>
>> add_one = x + 1
>>
>
> This takes the current value of x, adds one to it, and assigns it to the
> very badly named variable "add_one".
>
>
>
>  Can you provide some useful use cases for lambda functions?
>>
>
> Sorting with comparison or key functions.
> min or max with a key function.
> Callbacks.
> map
> reduce
> Solving numerical equations.
>
> There are probably others, but they're the obvious ones.
>
> Here's an example you can try:
>
> text = """Li Europan lingues es membres del sam familie. Lor separat
> existentie es un myth. Por scientie, musica, sport etc, litot Europa usa li
> sam vocabular. Li lingues differe solmen in li grammatica, li pronunciation
> e li plu commun vocabules. Omnicos directe al desirabilite de un nov lingua
> franca: On refusa continuar payar custosi traductores."""
> words = text.lower().split()
> sorted(words)  # sort in alphabetical order
>
>
> Now suppose you want to sort by the number of vowels. Here's how you can do
> it with an anonymous key function:
>
> sorted(words, key=lambda word: sum(word.count(c) for c in 'aeiou'))
>
>
> --
> Steven
>
>
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