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.ga...@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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