Simple question - end a raw string with a single backslash ?

[Roland Müller]

On 10/13/20 4:14 PM, Serhiy Storchaka wrote:
> 13.10.20 11:52, Tony Flury via Python-list пише:
>> I am trying to write a simple expression to build a raw string that ends
>> in a single backslash. My understanding is that a raw string should
>> ignore attempts at escaping characters but I get this :
>>
>>      >>> a = r'end\'
>>        File "<stdin>", line 1
>>          a = r'end\'
>>                    ^
>>     SyntaxError: EOL while scanning string literal
>>
>> I interpret this as meaning that the \' is actually being interpreted as
>> a literal quote - is that a bug ?
> r'You can\'t end raw string literal with a single "\"'
>
> If backslash be true inner in a raw string, the above literal would end
> after \'. It would be very hard to write a raw string containing both \'
> and \", and even \''' and \""" (there are such strings in the stdlib).
>
> So you have problem either with trailing backslash, or with inner
> backslash followed by quotes. Both problems cannot be solved at the same
> time. Python parser works as it works because initially it was easier to
> implement, and now this cannot be changed because it would break some
> amount of correct code.
>
>> The only solution I have found is to do this :
>>
>>      >>> a = r'end' + chr(92)
>>      >>> a
>>     'end\\'
>>      >>> list(a)
>>     ['e', 'n', 'd', '\\']
>>
>> or
>>
>>
>>      >>> a = r'end\\'[:-1]
>>      >>> list(a)
>>     ['e', 'n', 'd', '\\']
>>
>> Neither of which are nice.
> You can also write r'end' '\\'. It is not too nice, but it looks nicer
> to me then two other variants.
>
I used the triple single quotes as delimiter:

 >>> s = r'''a single quote ', a double quote "'''
 >>> s

'a single quote \', a double quote "'

BR,

Roland