unusual string notation

[krismc]

I've got a little routine that attempts to strip the 'Traceback (most recent call last):' & other verbage from an except Exception as e: report and store just the line nos cascade & error in a file. To my great consternation this routine occasionally crashes when trying to cleanup some reports.

Today's offender has some sort of backslash apostrophe notation I'm unfamiliar with. Indeed if I try to set a variable equal to the list on the cmd line, with a view to trying the routine 1 line at a time to see where it crashes, I get an error straight up

>>> a=[\'Traceback (most recent call last):\', \'  File "<stdin>", line 447, in <module>\', \'  File "<stdin>", line 295, in _send\', \'  File "<stdin>", line 80, in _getss\', \'  File "<stdin>", line 10, in _prnt\', \'KeyError: verbose\', \'\']
Traceback (most recent call last):
  File "<stdin>", line 1
SyntaxError: invalid syntax

Anybody know what's the deal with this notation & why it only appears occasionally in except Exception as e reports?

[peterhinch]

The problem is that the ' character is escaped by being prepended with a \. Compare

>>> a=[\'Traceback (most recent call last):\',]
Traceback (most recent call last):
  File "<stdin>", line 1
SyntaxError: invalid syntax

with

>>> a=['Traceback (most recent call last):',]
>>> 

Strings should be delimited with ' or " and not with \' or \".

[krismc]

Most exceptions look like your 2nd example Peter, any thoughts why the occasional one has the backslashes & what bit of code would be inserting them?

[peterhinch]

what bit of code would be inserting them?

Without seeing your code - or an example of an exception that causes the problem - it's hard to comment. Otherwise it would be easy to replace all instances of "\'" with "'".

[mendenm]

By any chance, are you calling __str__ or __repr__ on your traceback (indirectly, via str(traceback) or repr(traceback) , which would result in the whole thing being wrapped as a string, requiring internal escaping of the delimiters?

[krismc]

I don't Marcus, but I do remove the single & double inverted commas as part of the verbiage pruning & making it a savable text file, so maybe that is forcing in the back slashes? Wish I could figure out why it only happens sometimes!

…

On Fri, 21 Mar 2025, 10:07 pm Marcus Mendenhall, ***@***.***> wrote: By any chance, are you calling __str__ or __repr__ on your traceback (indirectly, via str(traceback) or repr(traceback) , which would result in the whole thing being wrapped as a string, requiring internal escaping of the delimiters? — Reply to this email directly, view it on GitHub <#16965 (reply in thread)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ACBCWGIFNPNQKKSMACWH6L32VPXGFAVCNFSM6AAAAABZMSDZE6VHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTENJXGYYDANY> . You are receiving this because you authored the thread.Message ID: ***@***.*** com>

[mendenm]

Can you post the original, complete traceback by just letting the error happen without catching it? Maybe some internal module is fiddling with the text. If so, we can see what module might be causing this.

[krismc]

The list I posted at the start of this thread is the sys.print_exception(e) style output my parser routine was working on when it crashed. My best guess is it crashed because of all the dodgy backslashes. There is something ouroborosy about an exception in an exception handler, I better do a search to make sure there is no repr() in there.

…

On Fri, 21 Mar 2025, 10:39 pm Marcus Mendenhall, ***@***.***> wrote: Can you post the original, complete traceback by just letting the error happen without catching it? Maybe some internal module is fiddling with the text. If so, we can see what module might be causing this. — Reply to this email directly, view it on GitHub <#16965 (reply in thread)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ACBCWGPLEQRDEDTPSBDXD532VP273AVCNFSM6AAAAABZMSDZE6VHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTENJXGYZTCOA> . You are receiving this because you authored the thread.Message ID: ***@***.*** com>

[mendenm]

that post wins the linguistics award for turning ouroboros into an adjective!

[krismc]

I wish I had more dexterity as a snake charmer Marcus, upython frequently bites me. Also I think ouroborosy is an adverb.

…

On Fri, 21 Mar 2025, 11:38 pm Marcus Mendenhall, ***@***.***> wrote: that post wins the linguistics award for turning ouroboros into an adjective! — Reply to this email directly, view it on GitHub <#16965 (reply in thread)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ACBCWGLSKV4HBX7RVCH44JT2VQB2VAVCNFSM6AAAAABZMSDZE6VHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTENJXGY4TQOA> . You are receiving this because you authored the thread.Message ID: ***@***.*** com>

[sosi-deadeye]

If you put the escape character / before the opening or closing quote (\' or \"), it's not recognized as the start or end of the str literal.

If you want to create this str: 'Traceback (most recent call last):'
Then there are following options to accomplish it:

• "'Traceback (most recent call last):'"
• """'Traceback (most recent call last):'"""
• '\'Traceback (most recent call last):\''
• '''\'Traceback (most recent call last):\''''

If you're working with the REPL and enter a name of an object, the representation is shown.

test = "Hello World"

Now just put the name into the repl:

test

You'll see the representation of the object test, which is a str. Representation means: You can copy the output and use it in source code, because it's already quoted and escaped correctly.

If you have an object like a list or tuple, the elements are also shown in their representation, even if you print the whole object:

test = "Hello World"
my_list = [test, test, test]

print(my_list) # here with added quotes from representation
print(my_list[0]) # print the first object from my_list. It's not the representation.

You should see this:

['Hello World', 'Hello World', 'Hello World']
Hello World

The first is the complete list, where all elements are printed in their representation.
The second is the first element. There are no quotes visible. It's not the representation.