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I have installed OpenCV and and access it with Python 2. However, I'm unable to use OpenCV with Python 3.

It says "Cannot open shared object".

ImportError: libQTtest.so.4: cannot open shared object file: no such file or directory

I have tried sudo cat /usr/local/lib and some other commands but I still can't get it to work.

How do I share OpenCV with Python 3 on a Raspberry Pi 3 B+?

I have also tried following the steps at https://github.com/cmusphinx/pocketsphinx-python/issues/6 and I have read this.

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  • How did you install OpenCV and the Python bindings? Did you just use apt-get install python-opencv? It'd also be helpful if you could rerun the code and get the exact, full error message you get rather than just the "Cannot open shared object" bit.
    – Aurora0001
    Commented May 6, 2018 at 15:35
  • libqtgui.so.4 cant be shared is the error message and also i did it with cmake thing
    – JohnConstantine
    Commented May 6, 2018 at 16:44
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    Try running sudo apt install libqtgui4 and then try again, @John. Let me know if you have any luck.
    – Aurora0001
    Commented May 6, 2018 at 17:03
  • @JohnConstantine , see this tutorial on installing opencv on stretch for python 2 or 3.
    – Benjamin Ashbaugh
    Commented May 6, 2018 at 17:04
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    What on earth is sudo cat /usr/local/lib supposed to accomplish, lol? It's gobbledygook, kind of like, "I put the car windows in reverse, but the steering wheel still won't open". Sorry, but you need to go into much more detail about exactly what you've done vis., "I installed..." and exactly when and what errors you are getting if you want someone else to troubleshoot this.
    – goldilocks ♦
    Commented May 6, 2018 at 18:25

2 Answers 2

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It says "Cannot open shared object".

ImportError:libQTtest.so.4:cannot open shared object file:no such file or directory

Yes, but it does not say this is because "the library isnt shared with it". What it says is, "no such file or directory".

As far as I can tell, libQTtest.so.4 is not actually part of openCV, although it is part of a GUI framework upon which openCV may depend.

According to the Debian package search (Raspbian is more or less Debian with some minor tweaks), this .so is part of package libqt4-test, which is available in the Debian current stable version, 9 ("stretch"), armhf compilation, so should be in Raspbian. You can install this with:

sudo apt install libqt4-test

This may drag in some other dependencies. Note if you are using a previous version of Raspbian it probably is not available.

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  • Thank you @goldilocks your command is work form me in : 1. raspberry pi 3 model B 2. python 3 3. opencv 3.4 4. os raspbian stretch 2018-10-09
    – panji19
    Commented Oct 31, 2018 at 9:56
  • This is still working on Raspberry Pi 4 B+ with opencv 4.2.2
    – alfred
    Commented Jun 18, 2020 at 6:44
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I have installed OpenCV and and access it with Python 2. However, I'm unable to use OpenCV with Python 3.

With python (Python 2) you have installed python-opencv from the repository which is the Python 2 version. If you try to use it with python3 this cannot work. You have to install OpenCV for the Python 3 version. Just do it with:

rpi ~$ sudo apt install python3-opencv
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