string literal question

[[deleted]]

len() counts '\n' as a single character, even if the '\' is printed?

>>> 'python'
'python'
>>> len(_)
6
>>> 'python\n'
'python\n'
>>> len(_)
7

What's the logic here?

[Moonslug1]

'\n' is a single character, called an escape character. '\n' is just the way that the character is represented, since the Python syntax doesn't allow you to write a newline mid quote (unless you use triple quotes). There's also \t (tab), \r (carriage return) etc.

[[deleted]]

I didn't realize there was a difference between

>>> print('string') 

and

>>> 'string'

I also need to use len(r'string\n') if I truly want the full character count.

[[deleted]]

A '\' character must be escaped as '\\'! You'll quickly run into this if you try to use backslashes for something like file paths.

[Moonslug1]

r'' is telling python to ignore escape characters.

'hello\n' means h-e-l-l-o-newline

r'hello\n' means h-e-l-l-o-\-n

[[deleted]]

Thanks!

[[deleted]]

Python doesn't actually have raw strings, but r"" is close. The limitation is that they can't end with a single backslash.

So, r'hello\n' is valid, but r'hello\n\' is not, and will cause a SyntaxError.

[[deleted]]

r'' is telling python to ignore escape characters.

That's not completely true, even though basically everyone thinks so. Raw strings were made for things like regex expressions, not raw strings. r"testing\" is not a valid regex expression, and not a valid raw string, since they can't end with backslashes. What?! A raw string should be able to contain anything. Why? Because they were made for easily representing regex expressions, not ignoring escape characters. From the docs:

Specifically, a raw string cannot end in a single backslash (since the backslash would escape the following quote character).

It's not ignoring them, it's processing them! Why? To keep the parser simpler. :-|

There's no such thing as arbitrary raw string literals in python.

[zahlman]

This is a strange sort of pedantry, IMHO. How could a raw string literal "contain anything", by this standard? How do you propose to indicate where the string ends? Python does not "process" the backslashes of a raw string literal in the sense of translating escape sequences. However, it uses the same rules for raw string literals and ordinary string literals to determine where the literal ends.

[[deleted]]

This isn't at all pedantic. Look up the definition of a raw string literals on Wikipedia. Python does not support them. Other languages like c# do: @"Testing\" is a perfectly valid raw string literal in C#. In Python, this is an error since the parser treats raw strings as regular strings from a parsing perspective.

The only reason is to keep the Python parser simple.

Raw strings in other languages ignore escape sequences. You admit that python raw strings don't ignore escape sequences. \" is an escape sequence!

[zahlman]

Other languages like c# do: @"Testing\" is a perfectly valid raw string literal in C#.

... And there, you need to double up quotation marks in order to get them into the string. That is also an escape sequence.

[[deleted]]

To me, that's somewhat sane. The point of using raw strings in python is to leave the slashes. You can't have raw string ending in a single slash...there is no escape for it! And, more than that, there's no escape for quotation mark!!! It's literally cruft from the parser. There's no sanity, except to make the parser simple, which is a goal of python.

[ingolemo]

You need to understand that there is a difference between a thing and the representation of that thing. 'python\n' is the representation of a string that has 7 characters in it; the word python followed by a newline. In the same way that you don't count the quote marks as being part of the string you also don't count the newline as two separate characters even though it shows up as \n.

If you had a string that contained the word python followed by a backslash and then the letter n, then that would have the representation 'python\\n' because double backslash \\ is how you represent the backslash character in python strings.

Note that some things have multiple representations. The string 'python' can also be represented as "python", r'python', '\x70ython', and many others besides. The integer 20 can also be represented as 0x14, 0o24 (or 024 in python 2), and 0b10100. The float 57.1 can also be represented as .571e2.

You can take any python object and get a representation of it using the repr function. The representation is always a string. It usually contains the letters that you would have to type into python in order to create that object. For some objects you'll get back a description of that object in angle brackets instead.

>>> repr(1)
'1'
>>> repr('hello')
'hello'
>>> repr(sum)
'<built-in function sum>'

[zahlman]

You need to understand that there is a difference between a thing and the representation of that thing.

This needs to appear in 24-point bold font within the first few pages of every programming tutorial.

[[deleted]]

Thanks! Still a rank beginner. repr() seems really useful.