Could not find a version that satisfies the requirement pypdf (from versions: none)

I'm having trouble installing pypdf, here is my error message after executing: pip install pypdf

   WARNING: Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.HTTPSConnection object at 0x7f012437ffa0>: Failed to establish a new connection: [Errno -3] Temporary failure in name resolution')': /simple/pypdf/
    WARNING: Retrying (Retry(total=3, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.HTTPSConnection object at 0x7f01243a0310>: Failed to establish a new connection: [Errno -3] Temporary failure in name resolution')': /simple/pypdf/
    WARNING: Retrying (Retry(total=2, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.HTTPSConnection object at 0x7f01243a0670>: Failed to establish a new connection: [Errno -3] Temporary failure in name resolution')': /simple/pypdf/
    WARNING: Retrying (Retry(total=1, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.HTTPSConnection object at 0x7f01243a0820>: Failed to establish a new connection: [Errno -3] Temporary failure in name resolution')': /simple/pypdf/
    WARNING: Retrying (Retry(total=0, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.HTTPSConnection object at 0x7f01243a09d0>: Failed to establish a new connection: [Errno -3] Temporary failure in name resolution')': /simple/pypdf/
    ERROR: Could not find a version that satisfies the requirement pypdf (from versions: none)
    ERROR: No matching distribution found for pypdf
    WARNING: There was an error checking the latest version of pip.

To be honest, I don't quite understand the error messages. From what I could see on the net the problem comes surely from opencv? I already try upgrating pip and the following command:

pip install opencv-python
pip install python-opencv
pip install opencv-contrib-python

But everytimes I got the same problem with "Could not find a version that satisfies the requirement"

> Temporary failure in name resolution

Your internet connection was bad. Try again later.
It might also be issues with your DNS configuration.

You can try ping pypi.org. The result should look like this:

64 bytes from 2a04:4e42:200::223 (2a04:4e42:200::223): icmp_seq=3 ttl=60 time=5.67 ms
64 bytes from 2a04:4e42:200::223 (2a04:4e42:200::223): icmp_seq=4 ttl=60 time=8.74 ms
64 bytes from 2a04:4e42:200::223 (2a04:4e42:200::223): icmp_seq=5 ttl=60 time=16.2 ms
64 bytes from 2a04:4e42:200::223 (2a04:4e42:200::223): icmp_seq=6 ttl=60 time=9.06 ms
64 bytes from 2a04:4e42:200::223 (2a04:4e42:200::223): icmp_seq=7 ttl=60 time=7.50 ms
64 bytes from 2a04:4e42:200::223 (2a04:4e42:200::223): icmp_seq=8 ttl=60 time=6.09 ms
64 bytes from 2a04:4e42:200::223 (2a04:4e42:200::223): icmp_seq=9 ttl=60 time=9.54 ms

If there is nothing happening, it's definitely your internet connection / DNS configuration. It's not related to any of the packages.

You can also check https://status.python.org/ - maybe PyPI has/had issues. But that is very rare.