[Tutor] if >= 0

[rahmad akbar]

Alan,

roger that and thanks a bunch. now replying with reply all, i am a super
noob and thanks for the kind adivce


On Tue, Feb 11, 2014 at 10:31 AM, ALAN GAULD <alan.gauld at btinternet.com>wrote:

> CCing the list. Please use Reply All when responding.
>
> > thanks Alan, i understand now zero is False.
>
> That's right. but...
>
> > so if one of the 'if' test is false, that 'for' loop is also halted?
> > and does not proceed to the next element?
>
> This bit  is wrong.
>
>
> The for loop will continue to completion every time.
>
>
> >>> for element in in_file:
> >>>   if  element.find(LOCUS'):
>
> >>>     locus += element
> >>>   elif element.find(...)
>
> What happens is that because the find(LOCUS) is the first test it will
> almost
> always be true. So the locus += element will be executed on almost every
> line
> Because that branch of the if construct is executed no other branch is
> executed.
>
> In an if/elif/else structure only one branch ever gets executed in a given
> iteration of the for loop. elif stands for "else if" so the test in the
> elif statements
> only get executed if all the preceding tests fail. So the order of the
> tests is
> very important. Now in your case the first branch nearly always succeeds
> and so the subsequent branches never get executed.
>
> When you add the >=0 condition you stop the first test from catching
> everything.
>
> So the lines that do not contain LOCUS now get tested for the other values
> and as a result update their respective string variables.
>
> But the for loop continues regardless of which branch is used, it is only
> controlled by the number of lines in the file. It does not care what the
> code
> inside the loop body does (unless it explicitly uses return or break or
> continue).
>
> HTH
>
> Alan g.
>



-- 
many thanks
mat
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