QDesktopServices.openUrl fails to open local file on Ubuntu

eyllanesc

@efremdan1 use the fullpath:

import os.path

CURRENT_DIRECTORY = os.path.dirname(os.path.realpath(__file__))
filename = os.path.join(CURRENT_DIRECTORY, "doc/_build/latex/xslide-user-manual.pdf")
print(filename)
url = QUrl.fromLocalFile(filename)
if not QDesktopServices.openUrl(url):
    print("failed")

JonB

@Christian-Ehrlicher said in QDesktopServices.openUrl fails to open local file on Ubuntu:

file:doc/_build/latex/xslide-user-manual.pdf

This no valid url

Do you mean because of the "relative" start to the path in file:doc/..."?

@efremdan1
You can do as @eyllanesc and others say and make your file path absolute before you start.

You can also read https://doc.qt.io/qt-5/qurl.html#fromLocalFile where the docs explain about local, relative files and URLs, especially the bottom example code there:

For this reason, it is better to use a relative URL (that is, no scheme) for relative file paths:
QUrl url = QUrl("file.txt");
QUrl baseUrl = QUrl("file:/home/user/");
// prints QUrl("file:///home/user/file.txt")
qDebug() << baseUrl.resolved(url);

Christian Ehrlicher

@JonB said in QDesktopServices.openUrl fails to open local file on Ubuntu:

Do you mean because of the "relative" start to the path in file:doc/..."?

No, it's simply no valid url since the schema must be <name>://.

JonB

@Christian-Ehrlicher
Oh, I didn't realize the // is a compulsory part of any schema!

Christian Ehrlicher

@JonB see e.g. here: https://doc.qt.io/qt-5/qurl.html#setAuthority - :// must be between the schema and the 'rest' :)

JonB

@Christian-Ehrlicher
Yes, thank you. I am not sure I had ever particularly been struck by that, but I see now!

So the obvious question might be: why did they need //? there must be a reason. Why not just /? Why didn't the first people who defined this settle on <name>:/?

JoeCFD

@JonB it could be http:// and local file is file://

JonB

@JoeCFD
My question is why didn't they go for, say, http:/ and file:/, instead of //, in the first place? Purely because I'm interested/wonder.

JoeCFD

@JonB sorry I misundestood your previous post. / is reserved for path.
check here https://en.wikipedia.org/wiki/URL out.

JonB

@JoeCFD said in QDesktopServices.openUrl fails to open local file on Ubuntu:

/ is reserved for path.

Again, I know that, my question was why adopt double-slashes. Interestingly (to me) I have come across a BBC interview from 2009 with Tim Berners-Lee where it states:

The forward slashes at the beginning of internet addresses have long annoyed net users and now the man behind them has apologised for using them.

Sir Tim Berners-Lee, the creator of the World Wide Web, has confessed that the // in a web address were actually "unnecessary".

He told the Times newspaper that he could easily have designed URLs not to have the forward slashes.

So there you are --- the choice of // was "annoying" and "unnecessary"! :)

efremdan1

@eyllanesc said in QDesktopServices.openUrl fails to open local file on Ubuntu:

@efremdan1 use the fullpath:
import os.path

CURRENT_DIRECTORY = os.path.dirname(os.path.realpath(file))
filename = os.path.join(CURRENT_DIRECTORY, "doc/_build/latex/xslide-user-manual.pdf")
print(filename)
url = QUrl.fromLocalFile(filename)
if not QDesktopServices.openUrl(url):
print("failed")

This answer works too, but I marked @JoeCFD's as the correct answer since it doesn't look necessary to use the absolute directly. Just using QDesktopServices.openUrl(QUrl.fromLocalFile("doc/_build/latex/xslide-user-manual.pdf")) works absolutely fine for me. And since it's a lot shorter and more readable, I don't see why not to use it.

eyllanesc

@efremdan1 I don't recommend using relative paths as they will depend on where the "current location" is. In your case it seems that you are executing the script of the form: python script.py but if at another time you execute it as python foo/script.py it may fail. Relative paths are one of the most common causes of silent errors that are the worst at debugging.

JonB

@efremdan1 said in QDesktopServices.openUrl fails to open local file on Ubuntu:

QUrl.fromLocalFile

Using QUrl.fromLocalFile(), instead of trying to type in the right file:// stuff, is fine and good.

However, passing a relative path to it, or specifying file:://relative-path, is dangerous precisely as @eyllanesc has said.

JoeCFD

@efremdan1 The other guys are right. I thought you might know this and therefore did not mention that in my post. Try to use absolute path as much as possible.

efremdan1

@eyllanesc said in QDesktopServices.openUrl fails to open local file on Ubuntu:

@efremdan1 I don't recommend using relative paths as they will depend on where the "current location" is. In your case it seems that you are executing the script of the form: python script.py but if at another time you execute it as python foo/script.py it may fail. Relative paths are one of the most common causes of silent errors that are the worst at debugging.

You're indeed correct. Thank you.