Traceback (most recent call last):
  File "/home/pi/.local/lib/python3.5/site-packages/serial/serialposix.py", line 265, in open
    self.fd = os.open(self.portstr, os.O_RDWR | os.O_NOCTTY | os.O_NONBLOCK)
PermissionError: [Errno 13] Permission denied: '/dev/serial0'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "Desktop/Old/mustwork.py", line 14, in <module>
    timeout=1
  File "/home/pi/.local/lib/python3.5/site-packages/serial/serialutil.py", line 240, in __init__
    self.open()
  File "/home/pi/.local/lib/python3.5/site-packages/serial/serialposix.py", line 268, in open
    raise SerialException(msg.errno, "could not open port {}: {}".format(self._port, msg))
serial.serialutil.SerialException: [Errno 13] could not open port /dev/serial0: [Errno 13] Permission denied: '/dev/serial0'

$ uname -a
Linux raspberrypi 4.14.79-v7+ #1159 SMP Sun Nov 4 17:50:20 GMT 2018 armv7l GNU/Linux

$ cat /boot/config.txt
enable_uart=1

$ grep -v ^# /boot/config.txt
enable_uart=1

$ ls -lh /dev/serial*
lrwxrwxrwx 1 root root 5 mai 18 20:59 /dev/serial0 -> ttyS0
lrwxrwxrwx 1 root root 7 mai 18 20:59 /dev/serial1 -> ttyAMA0

$ groups ${USER}
pi : pi adm tty dialout cdrom sudo audio video plugdev games users input netdev spi i2c gpio