# String Format byte order **URL:** \ **Category:** Ignition\ **Created:** [January 21, 2022, 10:14pm UTC](https://forum.inductiveautomation.com/t/string-format-byte-order/55276 "2022-01-21T22:14:03Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![paul1](https://avatars.discourse-cdn.com/v4/letter/p/3d9bf3/32.png) [@paul1](https://forum.inductiveautomation.com/u/paul1)\ **Post date:** [January 21, 2022, 10:14pm UTC](https://forum.inductiveautomation.com/t/string-format-byte-order/55276/1 "2022-01-21T22:14:03Z")
I have a string array in Omron NJ memory that is bound to CJ memory type “D” and manipulated by a vijeo designer HMI to display a recipe name. This is edited by the HMI and stored in the PLC array for manipulation. I am trying to replicate the HMI function in Ignition to allow editing the string text . The data is string characters are displaying byte swapped where " Recipe 123" is displaying as “eRicep1 32” How do I swap each pair of characters to read/write correctly? ---
**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\ **Post date:** [January 21, 2022, 10:24pm UTC](https://forum.inductiveautomation.com/t/string-format-byte-order/55276/2 "2022-01-21T22:24:32Z")
I would use a derived tag, with a character-swapping runScript() expression in both directions. ---
**Author:** ![paul1](https://avatars.discourse-cdn.com/v4/letter/p/3d9bf3/32.png) [@paul1](https://forum.inductiveautomation.com/u/paul1)\ **Post date:** [January 22, 2022, 1:48am UTC](https://forum.inductiveautomation.com/t/string-format-byte-order/55276/3 "2022-01-22T01:48:50Z")
Thanks, I was hoping there was an automatic function for this. I’ll need to practice my script writing, Cheers ---
**Author:** ![pascal.fragnoud](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pascal.fragnoud/32/24728_2.png) [@pascal.fragnoud](https://forum.inductiveautomation.com/u/pascal.fragnoud)\ **Post date:** [January 24, 2022, 3:44pm UTC](https://forum.inductiveautomation.com/t/string-format-byte-order/55276/4 "2022-01-24T15:44:12Z")
Just so you don’t scratch your head for too long on this: ```python s = "eRicep1 32" s = ''.join(c for pair in zip(s[1::2], s[::2]) for c in pair) ``` `s[1::2]` and `s[::2]` will produce strings with even or odd characters ([1::2] = start from 1, stop at the end, step 2), `zip` will take one character from each, then it’s simply a matter of putting things in the right order. So, with `"eRicep1 32"`, `s[1::2]` will be `"Rcp 2"` and `s[::2]` `"eie13"` `zip("Rcp 2", "eie13")` produces the pairs `[('R', 'e'), ('c', 'i'), ('p', 'e'), (' ', '1'), ('2', '3')]` and iterating through those pairs and picking single extracts them from the tuples to produce the list `['R', 'e', 'c', 'i', 'p', 'e', ' ', '1', '2', '3']` All that’s left to do is join them on nothing with `''.join()` There might be libraries with builtins for this, but, well… ---
**Author:** ![paul1](https://avatars.discourse-cdn.com/v4/letter/p/3d9bf3/32.png) [@paul1](https://forum.inductiveautomation.com/u/paul1)\ **Post date:** [January 25, 2022, 1:20am UTC](https://forum.inductiveautomation.com/t/string-format-byte-order/55276/6 "2022-01-25T01:20:41Z")
Thanks Pascal, Managed to script a solution which works fine. See below **Script** Swap def ByteSwap(text): ## Swap each pair of characters to match byte order of string characters result ="" #clear result if (len(text)%2) ==1: # test if odd number of bytes text=text+" " #Add extra character for x in range (1,len(text),2): #loop through each second byte of entire string result = result+(text) #add second character result =result+(text[x-1]) #add first character return result #output final concatenated byte swapped string **Derived Tag Read expression** runScript(“Swap.ByteSwap”,0,{source}) **Derived Tag Write expression** runScript(“Swap.ByteSwap”,0,{value}) Thanks **Paul Reynolds** **Electrotech Controls Ltd** Automation & Controls Manager **P** 06 835 2260 **F** 06 835 2253 **M** 021 431 153 **E** [paul@electrotech.co.nz](mailto:paul@electrotech.co.nz) **W** [www.techgroup.co.nz](http://www.techgroup.co.nz/) 12 Sheffield Place, PO Box 3016, Napier 4142, New Zealand ![image001.jpg](https://us1.discourse-cdn.com/inductiveautomation/original/3X/a/a/aa645ef5c59caf22a3fcd1291c0dbe775b95dd91.jpeg) A member of the Tech Group of Companies Ltd ![image002.jpg](https://us1.discourse-cdn.com/inductiveautomation/original/3X/f/0/f003192a1f3cbff81737c51a6c1ed5f5dd97394e.jpeg) ---
**Author:** ![paul1](https://avatars.discourse-cdn.com/v4/letter/p/3d9bf3/32.png) [@paul1](https://forum.inductiveautomation.com/u/paul1)\ **Post date:** [January 25, 2022, 1:23am UTC](https://forum.inductiveautomation.com/t/string-format-byte-order/55276/7 "2022-01-25T01:23:40Z")
Thanks Pascal, Managed to script a solution which works fine. See below Script Swap ```python def ByteSwap(text): ## Swap each pair of characters to match byte order of string characters result ="" #clear result if (len(text)%2) ==1: # test if odd number of bytes text=text+" " #Add extra character for x in range (1,len(text),2): #loop through each second byte of entire string result = result+(text[x]) #add second character result =result+(text[x-1]) #add first character return result #output final concatenated byte swapped string ``` Derived Tag Read expression `runScript("Swap.ByteSwap",0,{source})` Derived Tag Write expression `runScript("Swap.ByteSwap",0,{value})` Cheers ---
**Author:** ![pascal.fragnoud](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pascal.fragnoud/32/24728_2.png) [@pascal.fragnoud](https://forum.inductiveautomation.com/u/pascal.fragnoud)\ **Post date:** [January 25, 2022, 9:08am UTC](https://forum.inductiveautomation.com/t/string-format-byte-order/55276/8 "2022-01-25T09:08:17Z")
It’s a good thing you found a solution by yourself, but I’d suggest you use the snippet I posted above. It’s a more pythonic way of doing things, using very pythonic things (zip, generators, comprehensions…) ```python def swap_bytes(s): return ''.join(c for pair in zip(s[1::2], s[::2]) for c in pair) ``` If it’s a bit too obscure as it is, I’ll deconstruct and explain it in more details. On the other hand, there is the `struct` library that could allow you to do this, but frankly I’m not familiar with it and couldn’t help figure out how to use it.