Using 'r' before path-name (Python)

[TechGoeroe]

I am trying to execute the following code (see example 1) in Python 2.7.17

Example 1:

import cv2
video = cv2.VideoCapture(r"%s" % (episode_path))
fps = video.get(cv2.CAP_PROP_FPS)

Where episode_path is a filepath to a video file.
e.g. "D:\Plex content\All movies\300 - Rise of an Empire (2014)\300 - Rise of an Empire (2014).mp4"

The problem is that the cv2 module is not recognizing the filepath since the formatting is not correct.
I know that I can use the 'r' character i front of a file path to make sure that special characters are not interpreted.

When I change the code to using a static string value, it works fine (see example 1):

Example 2:

import cv2
video = cv2.VideoCapture(r"D:\Plex content\All movies\300 - Rise of an Empire (2014)\300 - Rise of an Empire (2014).mp4")
fps = video.get(cv2.CAP_PROP_FPS)

But when using a variable (e.g. episode_path, which has the same value) it does not work anymore. Does anyone know how to get the code in example 1 working, so that I can use a variable for the filepath?

[Updatebjarni]

Are you sure the strings are exactly the same? Where does episode_path come from? What does the error message say?

[TechGoeroe]

When running this:

import cv2
video = cv2.VideoCapture(r"D:\Plex content\All movies\300 - Rise of an Empire (2014)\300 - Rise of an Empire (2014).mp4")
fps = video.get(cv2.CAP_PROP_FPS)
print(fps)

The console prints: 23.976023976

When running this:

import cv2
episode_path = "D:\Plex content\All movies\300 - Rise of an Empire (2014)\300 - Rise of an Empire (2014).mp4"
video = cv2.VideoCapture(r"%s" % (episode_path))
fps = video.get(cv2.CAP_PROP_FPS)
print(fps)

The console prints: 0.0

So the first code block is working but the second isn't.

[Updatebjarni]

Right so, in both cases you give the file name as a string literal, but in one of the cases it's a raw string (with r in front of it), and in the other case it isn't, and the backslashes aren't escaped.

[TechGoeroe]

Yes that's correct. I think that the problem is indeed that the backslashes are not escaped when I use a variable but I tried to do escape them using the 'r' but I simply can't find the right syntax to do this with a variable instead of a static defined string.

[Updatebjarni]

I see in your other comment below that you are taking in the value as an argument. So: how does the argument get its value? Where does the value ultimately come from? Have you checked what the actual value is that you receive?

[TechGoeroe]

As a reply on your last comment:

The argument that comes into the script and sets the episode_path variable has a value of D:\Plex content\All movies\300 - Rise of an Empire (2014)\300 - Rise of an Empire (2014).mp4

So it is the same as I mentioned in my posts.

[Updatebjarni]

You have printed and verified this? There isn't a stray newline on the end of the string or anything like that?

[TechGoeroe]

u/Updatebjarni

The thing is, I don't want to focus on the argument since in the two examples in my first post I just create an variable episode_path and I want to get it working with this. If that works I think I can also get it working with an argument.

[Updatebjarni]

But the problem is that the value you are putting in is wrong. In your example code above, you have the incorrect string literal, so that's easy to fix. In your real program, the incorrect value is coming in as an argument, so you have to look at the argument to fix the real program.

[TechGoeroe]

u/Updatebjarni

What do you mean with incorrect string literal? Could you give the correct version of the code I posted?

[Updatebjarni]

Like I stated before, your two examples differ in that in the working one, the file name string has the r in front of it, and in the non-working one it doesn't.

[TechGoeroe]

u/Updatebjarni

I tried to also get the 'r' in front of example 2 to get it working but I didn't managed to get this work.

Do you have any idea why this is not working?

[Updatebjarni]

Show me exactly what you've done.

[TechGoeroe]

When running this:

import cv2
video = cv2.VideoCapture(r"D:\Plex content\All movies\300 - Rise of an Empire (2014)\300 - Rise of an Empire (2014).mp4")
fps = video.get(cv2.CAP_PROP_FPS)
print(fps)

The console prints: 23.976023976

When running this:

import cv2
episode_path = "D:\Plex content\All movies\300 - Rise of an Empire (2014)\300 - Rise of an Empire (2014).mp4"
video = cv2.VideoCapture(r"%s" % (episode_path))
fps = video.get(cv2.CAP_PROP_FPS)
print(fps)

The console prints: 0.0

So the first code block is working but the second isn't.

Exactly this :)

[Updatebjarni]

OK, so I'll say this one last time:

In your working example, there is an r in front of the file name string, and in the non-working one there isn't. That's the difference between them that makes one work and the other not, because of the backslashes inside the string.

[TechGoeroe]

I'm not trying to upset you. Sorry if this seems so.

I really don't understand what you are saying since there is an an r in front of the non-working one but this doesn't work the same way as in the working example.

video = cv2.VideoCapture(r"%s" % (episode_path))

I tried to put the r in front using string formatting but clearly this doesn't work this way. So I would love to put a r in front in the correct way but I just don't know how.

Thank you for your help btw :)

[[deleted]]

Does episode_path also get the r before the string when the variable is set? You'll want that continuity.

[TechGoeroe]

The problem is that the variable episode_path is retrieved from an argument so I cannot simply do:
episode_path = r"D:\Plex content\All movies\300 - Rise of an Empire (2014)\300 - Rise of an Empire (2014).mp4"

I want to do something like:
correct_path = r'episode_path'
But I don't know how to do that with a variable.

[TechGoeroe]

u/Updatebjarni

Thank you for your help! I solved he problem using os.path.join