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Asked — Edited
Resolved Resolved by ptp!

Strange Issue With File.Appendstring


I have a very strange issue with File.AppendString.

I have a very simple python script to write a text in a file:


file = "C:\Users\FredWin\Documents\ARC\Scripts\ten.txt"

File.AppendString(file, "text")
but it returns me


Caractères non conformes dans le chemin d'accès.
Done (00:00:00.0224805)
(trad:"Illegal characters in the path").

What is very strange is that some really simple file names are problematic and others are not.

For example "nine.txt" or "ten.txt" return the error, but not "eight.txt" or "eleven.txt".
Another example: if I use files such as "10.txt", "20.txt" or "30.txt", I have the error, but if I use "40.txt", "50.txt" and above, I have not.

I am really puzzled and I fail to see any logic in it.

Any idea what happens?

Edit: it seems to be specific to Python, I have not the same issue with EZ-scripts...

Related Hardware EZ-B v4
Related Control Script


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#1   — Edited
The problem you are experiencing is related to the escaping character "\" and is common to Javascript, Python, Java, C#, C++, C, Objective-C, Swift, and probably many other languages the exception so far is VBScript and EZ-Script.

So when you want to use a specific character in a string you use the escape char \ some examples:


Horizontal Tab is replaced with \t
Vertical Tab is replaced with \v
Nul char is replaced with \0
Backspace is replaced with \b
Form feed is replaced with \f
Newline is replaced with \n
Carriage return is replaced with \r
Single quote is replaced with \'
Double quote is replaced with \"
Backslash is replaced with \\
Python handles the escaped strings, doing the transformation, string is sent to ARC File class, then to windows file systems APIS, generating the error you are observing.

escape the slash e.g. "C:\\Users\\FredWin\\Documents\\ARC\\Scripts\\ten.txt"

Python has a few solutions to solve and simplify some problems, but, you are mixing implementations e.g. Python with Arc's File object and simple things like using the universal path concept e.g. "c:/Users/FredWin/Documents/Arc/Scripts/ten.txt" may not work outside of the Python standard library.
Thanks @ptp. It works!

It is really strange, though, that it works systematically for some files (ex: "eight.txt") and for other it systematically doesn't (ex: "ten.txt"), with the exact same syntax...
The magic of informatics, I guess:D
There is no magic:)

"c:\SomeFolder\eight.txt"  => \e is not a valid escaped character is ignored and the final strings is: "c:\SomeFolder\eight.txt"
"c:\SomeFolder\ten.txt"  => \t is a TAB (value 9 in ASCII table) is translated and the final string is "c:\SomeFolder(TAB)ten.txt"
OK, I see the logic with the escaped characters.
But just out of curiosity, why is it not working for "3.txt", "30.txt", "4.txt" and "5.txt", but it works for "40.txt" and "50.txt" ?
#5   — Edited
Short answer:
\3 = ASCII char 3
\30 = ASCII char 24
\40 = ASCII char 32 = Space
\50 = ASCII char 40 = (
The first printable char in ASCII is the space, decimal value 32 or octal value 040 so:
\0 to \39  will be translated to a non printable character and will be invalidated by the filesystem API calls.

Food for the brain:

String literals e.g. \000 and \0x \t etc:

ASCII table in decimal, octal and hex:

Octal numeral system:

Decimal (10) base to Octal (8) base:

Octal base (2 ^3) to Decimal (10 ^ 1) base:
OK, I get it!
Thanks again for your help. I learned a lot, as usual:)