Python Syntax White Spaces

Question

Evening,

This is not necessarily pythonic, I know that going into it. However, I can not get this to trigger properly at all.

What I'm trying to do is match two letters to items in "registers" which is getting done correctly, however I'm then trying to see if there is a white space after those two letters. The white space is what's not getting picked up correctly. I'm sure that I'm just botching up the sytax. Any help would be greatly appreciated.

registers = ['R0','R1','R2','R3','R4','R5','R6','R7']
whiteSpace = ['\t', ' ']
if (item[idx +2] + item[idx +3]) in registers and (item[idx +4] in whiteSpace):

you should probably look at pyparsing ... assuming you are trying to make some kind of grammar — Joran Beasley
– Joran Beasley, Commented Oct 2, 2012 at 4:22
No errors. My test cases are just not working correctly. Also to note I can't use any string helper classes or regest for this. — Miscue
– Miscue, Commented Oct 2, 2012 at 4:32
Nothing is obviously wrong there. We would need to see your particular item and idx values where it fails. — Vaughn Cato
– Vaughn Cato, Commented Oct 2, 2012 at 4:36
idx is just an integer at this point. My test cases are "R3 " and R4 " — Miscue
– Miscue, Commented Oct 2, 2012 at 4:38
You realize that "R3 " and "R4 " won't work unless idx is -2, right? — Mark Reed
– Mark Reed, Commented Oct 2, 2012 at 4:39

Matthew Trevor · Accepted Answer · 2012-10-02 05:10:40Z

1

It's hard to tell what you're doing wrong without seeing an example of what item is or why you're stepping through it with an index pointer. If it's just a string, as you say, you can reduce the test to the following:

if item[:2] in registers and item[-1] in whiteSpace:

You'll need to guarantee that item is 3 chars long, or put another guard in the condition.

As an aside, I like to use named slices for this sort of thing to make the intent more obvious:

code = slice(0, 2)
spacer = slice(-1)

if item[code] in registers and item[spacer] in whiteSpace:

edited Oct 2, 2012 at 5:10

answered Oct 2, 2012 at 5:04

Matthew Trevor

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