Python3-3.7.3: cannot run pdb

[Rich Shepard]

Running python3-3.7.3 on Slackware-14.2.

I'm trying to debug a module using pdb but failing with all attempts. For
example, using breakpoint() at the line where I want to stop the running
module and examine each line's execution, the program runs to completion and
shows there's a syntax error:

$ python3 geochem.py
   File "geochem.py", line 35
     boxchoices = ttk.Combobox(self, textvariable=med,
              ^
SyntaxError: invalid syntax

Importing pdb and inserting pdb.set_trace() produces the same output.

invoking pdb from the command line produces a full back trace:

$ python3 -m pdb geochem.py 
Traceback (most recent call last):
   File "/usr/lib/python3.7/pdb.py", line 1701, in main
     pdb._runscript(mainpyfile)
   File "/usr/lib/python3.7/pdb.py", line 1570, in _runscript
     self.run(statement)
   File "/usr/lib/python3.7/bdb.py", line 585, in run
     exec(cmd, globals, locals)
   File "<string>", line 1, in <module>
   File "/home/rshepard/development/openEDMS/views/geochem.py", line 35
     boxchoices = ttk.Combobox(self, textvariable=med,
              ^
SyntaxError: invalid syntax

I don't understand the source of the syntax error and I'm not able to allow
pdb to step through the code.

Your advice appreciated,

Rich