MathLinkException: MathLinkException 22: MLNextPacket called while the current packet has unread data.

[RClarkPhysics]

Hi b3m2a1,
I was to follow your guide from:
https://community.wolfram.com/groups/-/m/t/1468475

and when I run this block of code:
ker = SubprocessKernel()
def MEval (expr, wait = True, kernel = ker) :
" " "MEval evaluates a Mathematica expression in the Mathematica kernel" " "
kernel.drain() # just to make sure things are clen
return kernel.evaluate (expr, wait = wait)
ker.start()
ker.start_evaluator()

I get this error:
MathLinkException Traceback (most recent call last)
in
4 kernel.drain() # just to make sure things are clen
5 return kernel.evaluate (expr, wait = wait)
----> 6 ker.start()
7 ker.start_evaluator()

~/Library/Mathematica/Paclets/Repository/PJLink-1.1.2/SubprocessKernel/SubprocessKernel.py in start(self)
47
48 kernel_open = M.SubprocessKernel_OpenSubprocessNotebook(StartREPL=False)
---> 49 self.evaluate(kernel_open)
50
51 @Property

~/Library/Mathematica/Paclets/Repository/PJLink-1.1.2/PJLink/KernelLink.py in evaluate(self, expr, wait)
112 return self._reader.evaluate(expr, wait = wait)
113 else:
--> 114 return self._evaluate(expr, wait = wait)
115
116 def evaluateString(self, expr, wait=True, **opts):

~/Library/Mathematica/Paclets/Repository/PJLink-1.1.2/PJLink/KernelLink.py in _evaluate(self, expr, wait)
105 self._evaluateExpr(self.M._add_type_hints(expr))
106 if wait:
--> 107 self.waitForAnswer()
108 return self.get()
109

~/Library/Mathematica/Paclets/Repository/PJLink-1.1.2/PJLink/KernelLink.py in waitForAnswer(self)
148 self.__accumulatingPS = [] # some old-ass setting for working with PostScript I assume
149 while True:
--> 150 pkt = self._nextPacket()
151 allowDefaultProcessing = self.notifyPacketListeners(pkt)
152 if allowDefaultProcessing:

~/Library/Mathematica/Paclets/Repository/PJLink-1.1.2/PJLink/KernelLink.py in _nextPacket(self)
1404 mark = LinkMark(self).init()
1405 try:
-> 1406 pkt = self.active_link._nextPacket()
1407 except MathLinkException as e:
1408 if e.name == "UnknownPacket":

~/Library/Mathematica/Paclets/Repository/PJLink-1.1.2/PJLink/NativeLink.py in _nextPacket(self)
232 def _nextPacket(self):
233 with self._wrap():
--> 234 return self._call("NextPacket")
235
236 def _endPacket(self):

~/Library/Mathematica/Paclets/Repository/PJLink-1.1.2/PJLink/HelperClasses.py in exit(self, type, value, traceback)
465 self.parent.thread_lock.release()
466 if self.checkError:
--> 467 self.parent._check_error(self.check)
468
469 ###############################################################################################

~/Library/Mathematica/Paclets/Repository/PJLink-1.1.2/PJLink/NativeLink.py in _check_error(self, allowed)
215 errCode = self._call("Error")
216 if self._isException(errCode, allowed):
--> 217 raise MathLinkException(errCode, self._call("ErrorMessage"))
218
219 def _connect(self):

MathLinkException: MathLinkException 22: MLNextPacket called while the current packet has unread data.

Do you have any idea what I could be doing wrong here?
I'm running this on python 3.7.4 on jupyter notebook
OS: macOS 10.15.2

Thank you for your time

[YechenZhou]

I have the same problem as you. Have you solved it ? @RandarserousRex @b3m2a1

[RClarkPhysics]

I couldn't solve it. I ended taking a completely different approach to getting my project to work.

apologies