[Tutor] map() and lambda to change class instance attribute (fwd)

[Joe Healy]

Alan Gauld wrote:

>>now I always used map() to perform a looped call on a function that
>>would change the attribute value, as shown in Mark Lutz & David
>>Ascher's Learning Python:
>>
>># Perform attribute value change on a single instance
>>def iterateInstances( oInstance ):
>>      oInstance.value = myValue
>>
>># Loop over list of instances
>>map( iterateInstances, aListOfInstances )
>>    
>>
>
>How bizarre. I'm astonished that Lutz/Ascher even show that as a means
>of changing an attribute. As Danny said, it's definitely an abuse of
>map,
>and there is no advantage whatsoever, as far as I can see. In fact I
>suspect that it's actually slower than an explicit loop (because of
>the extra list building).
>  
>
I have just been looking at
http://www.python.org/moin/PythonSpeed/PerformanceTips#loops
and whilst the examples do not show anything like this, they describe
the map function as a for moved into C code.
Could be confusing. Does not mention anything about return a list.


>  
>
>>However I was looking into lambdas in hope to eliminate the need to
>>define a function.
>>    
>>
>
>And a loop also avoids the need for a function, and therefore for
>a function call, which is another reason the map should be slower.
>
>Its completely weird that a text book should even suggest that map
>be used for this!
>
>Alan G
>Author of the Learn to Program web tutor
>http://www.freenetpages.co.uk/hp/alan.gauld
>
>_______________________________________________
>Tutor maillist  -  Tutor at python.org
>http://mail.python.org/mailman/listinfo/tutor
>  
>


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