Python counts 2 backslashes as 4?

Question

So, basically I'm trying to put a variable in a directory string, so here's what I got

os.startfile(r'C:\Users\User\Downloads\Alfred\start\\'+sentence+".exe")

But when I'm trying to run the script (the other code doesn't have anything to do with this error), this comes up:

    os.startfile(r'C:\Users\User\Downloads\Alfred\Open\\'+sentence+'.exe')
FileNotFoundError: [WinError 2] The system cannot find the file specified: 'C:\\Users\\User\\Downloads\\Alfred\\Open\\\\badlion.exe'

It somehow counts "\\" as "\\\\", when I try to put "\" instead of "\\" it counts the variable (sentence), as a string??? Please help, I'm new to Python.

It's a raw string. \ in a raw string is \\ in a normal string. \\ in a raw string is therefore \\\\ — Zoe, Oct 07 '20 at 06:55
can you print `sentence`? it seems as if it also contain `\\` — David, Oct 07 '20 at 06:55
Basically, I'm making a virtual assistant, and it will do things for you, I'm positive I didn't accidentally say "backslash" — , Oct 07 '20 at 07:01
I said "bob open badlion", and since I used code to remove "bob" and "open", it prints "badlion" — , Oct 07 '20 at 07:03
How about `f-strings`? `os.startfile(f"C:\Users\User\Downloads\Alfred\start\{sentence}.exe")` — PythonSherpa, Oct 07 '20 at 07:04
Anyway, the problem here is that even raw strings will do some primitive backslash processing, namely, for quote-chars, so, raw strings cannot end with an odd-number of backslashes. You can read about it at the bottom of [this section of the docs](https://docs.python.org/3/reference/lexical_analysis.html#string-and-bytes-literals) — juanpa.arrivillaga, Oct 07 '20 at 07:05
PythonSherpa, a bunch of errors come up on my IDE Error: SyntaxError: EOL while scanning string literal — , Oct 07 '20 at 07:06
Now it says "SyntaxError: (unicode error) 'unicodeescape' codec can't decode bytes in position 2-3: truncated \UXXXXXXXX escape" and it points to the "f" — , Oct 07 '20 at 07:09
Are you *trying* to put two backslashes there? Because that is, in fact, what you are doing — juanpa.arrivillaga, Oct 07 '20 at 07:11
As I said in the post, if I put 1 backslash instead of 2, it contains the variable inside the string — , Oct 07 '20 at 07:13
**What are you trying to do**? And **again** what version of Python are you using? Note, `'C:\\Users\\User\\Downloads\\Alfred\\Open\\\\badlion.exe'` is a string with *two* backslashes there at the end, not 4. Go ahead and `print('C:\\Users\\User\\Downloads\\Alfred\\Open\\\\badlion.exe')` Did you want two? Or one? — juanpa.arrivillaga, Oct 07 '20 at 07:14
I'm trying to have the script open a program, but as I said multiple times, if I put 1 backslash instead of 2 it will count the variable after it as a string, and if I don't have the r, it will also count the variable as a string. — , Oct 07 '20 at 07:19
@CraftYun83 I didn't ask you that, *I understand that*, **please answer my question**: do you want **one** or *two* backslashes? **What version of python are you using**. If it's *one* maybe the easiest is to use the answer by @TimurU but really, you should be using `pathlib` — juanpa.arrivillaga, Oct 07 '20 at 07:20
I want 1 backslash because 2 backslashes are not a valid directory. Im using Python 3.8, and @TimurU's answer didn't works since there is 2 backslashes — , Oct 07 '20 at 07:28
@CraftYun83 no, Timur's solution **only has single backslashes**. Go ahead an `print('C:\\Users\\User\\Downloads\\Alfred\\start\\'+sentence+".exe")`, what do you see? — juanpa.arrivillaga, Oct 07 '20 at 07:31
@CraftYun83 the representation of a string with a single backslash in Python produces two backslashes. __But the string itself still contains only one backslash__. — Błażej Michalik, Oct 07 '20 at 07:51

Timur U · Answer 1 · 2020-10-07T07:33:24.330

2

R string may give error with end symbol
But not error using \ - double slash

Use:

os.startfile('C:\\Users\\User\\Downloads\\Alfred\\start\\'+sentence+".exe")

But this type:

r’some text\’

may be error end of string

r’some text\\’

Will give double slash at end

edited Oct 07 '20 at 07:33

answered Oct 07 '20 at 07:19

Timur U

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Comments are not for extended discussion; this conversation has been [moved to chat](https://chat.stackoverflow.com/rooms/222688/discussion-on-answer-by-timur-u-python-counts-2-backslashes-as-4). – Samuel Liew Oct 07 '20 at 23:56

score 1 · Answer 2 · answered Oct 07 '20 at 07:46

If you want to workaround the problem with the \ at the end of your raw-string, in this case you may also use formatted-raw-strings:

os.startfile(fr'C:\Users\User\Downloads\Alfred\start\{sentence}.exe')

Provided, of course, the file under that path actually exists on your OS.

score 0 · Answer 3 · answered Oct 07 '20 at 07:10

0

You have to understand the difference between raw string literals, normal strings, and how repr() deals with them.

raw = r"raw string: \ \\ \\\\"
normal = "normal string: \ \\ \\\\"

print(raw, repr(raw), normal, repr(normal), sep='\n')

Outputs:

raw string: \ \\ \\\\         
'raw string: \\ \\\\ \\\\\\\\'
normal string: \ \ \\         
'normal string: \\ \\ \\\\'

Every slash in a raw string literal is treated as an actual slash
The path in the exception message is rendered using repr()

Therefore, each slash in your raw string literal will add two slashes in the exception message. But there's only one slash in the variable, and that's what python functions will see:

> print(raw[-1], normal[-1])

\ \

answered Oct 07 '20 at 07:10

Błażej Michalik

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If I put 1 backslash instead of 2 it thinks "sentence"( a variable) is a string... – Oct 07 '20 at 07:15
@CraftYun83 What do you mean "it thinks sentence is a string"? The answer above shows why your traceback looks like there are more slashes than you've added. You have 1 slash in each path segment and 2 before `+ sentence` , so the exception will show 2 slashes between each directory in the path, and 4 (r`'\' * 2`) right before `sentence`. – Błażej Michalik Oct 07 '20 at 07:18
@CraftYun83 yes, because then it escapes the single-quote – juanpa.arrivillaga Oct 07 '20 at 07:19
@juanpa.arrivillaga what double quote..? – Błażej Michalik Oct 07 '20 at 07:20
@BłażejMichalik I misspoke, I meant single-quote, `r'blah blah blah \' blah blah blha'` is one big string, because `\'` still escapes the quote in a raw string. – juanpa.arrivillaga Oct 07 '20 at 07:21
@juanpa.arrivillaga still, not the case here. It happens only if the single-quote is unbalanced, which is not the case in OPs question. – Błażej Michalik Oct 07 '20 at 07:25
1

@BłażejMichalik sure, but I'm almost certain taht is what the OP is referring to when they said: "when I try to put "\" instead of "\\" it counts the variable (sentence), as a string" which is not a case the OP is showing. – juanpa.arrivillaga Oct 07 '20 at 07:27
@CraftYun83 ok, please show how exactly the line of your code that lead to "it thinks `sentence` is a string" looks. – Błażej Michalik Oct 07 '20 at 07:30
I can't comment pictures – Oct 07 '20 at 07:33
@CraftYun83 you don't need pictures. – juanpa.arrivillaga Oct 07 '20 at 07:34
In Pycharm, string is green, variables are white, the variable "sentence" is green, not white – Oct 07 '20 at 07:40
@CraftYun83 just copy-paste it. Why you want to use pictures? We just want to see the line, we don't need to see how pycharm highlights it – Błażej Michalik Oct 07 '20 at 07:40
Anyway, just use `os.startfile(fr'C:\Users\User\Downloads\Alfred\start\{sentence}.exe)'`... – Błażej Michalik Oct 07 '20 at 07:43
os.startfile('C:\Users\User\Downloads\Alfred\open\'+sentence+'.exe') – Oct 07 '20 at 07:45
doesn't work... is there any other module besides os, that can open files and will actually work? – Oct 07 '20 at 07:46
@CraftYun83 that module works. **Again** your path is *incorrect*. This is not the a problem with `os` – juanpa.arrivillaga Oct 07 '20 at 07:50

Python counts 2 backslashes as 4?

3 Answers3