[Tutor] "if clause" in list comprehensions.

[Emile van Sebille]

On 10/19/2009 12:20 PM Alan Gauld said...
> 
> "Sander Sweers" <sander.sweers at gmail.com> wrote
> 
>>> mylist = ['John', 'Canada', 25, 32, 'right']
>>> a = [item.upper() for item in mylist if type(item) == type('good')]
>>
>> Usually it is recommended to use hasattr() instead of type()
>>    hasattr(s, 'upper')
> 
> Nope, they do  completely different things
> I think you might be thinking of isinstance() which can be used instead 
> of type(). I see you use hasattr as a means of testing for a method but 
> that is still different from testing type - the method names might be 
> the same but the functions be completely different in effect!
> 
>>> returned this: ['JOHN', 'CANADA', 'RIGHT']
>>> I was expecting this: ['JOHN', 'CANADA', 25, 32, 'RIGHT']
>>> So, actually the "if" acted like a filter.
> 
> It is intended to be used as a filter.
> 
>>> In order to use a list comprehension I created this function instead.
>>> def upperfy(item)
>>>    try:
>>>        item = item.upper()
>>>    except AttributeError:
>>>        pass
>>>    return item
> 
>> I would move return item under the except and remove the pass, other
>> might disagree on this.
> 
> I would :-)
> Doing that would result in None being returned for each successful 
> conversion. The OPs code is correct (even if unnecessary)
> 
>>> a = [upperfy(item) for item in mylist]
> 
> a = [item.upper() if type(item) == str else item for item in mylist]
> 
> should do it I think.

or even

   a = [ str(item).upper() for item in mylist ]

Emile


> 
> HTH,
> 
>