print help text in try-exception in python

Question

in a try-exception block in python, like shown below, I want my help message to be printed, instead of python's own error message. Is this possible?

 def genpos(a):
    ''' Generate POSCAR :
        Some error message'''
    try:
      tposcar = aio.read(os.path.join(root,"nPOSCAR"))
      cell = (tposcar.get_cell())
      cell[0][0] = a
      cell[1][1] = math.sqrt(3)*float(a)
      tposcar.set_cell(cell, scale_atoms=True)
      aio.write("POSCAR", tposcar, direct=True)
    except:
      help(genpos)
      sys.exit()

So, say, when this code is called without an argument, I want to get "Generate POSCAR : Some error message" instead of, python's Traceback (most recent call last):

  File "submit.py", line 41, in <module>
    main()
  File "submit.py", line 36, in __init__
    ase_mod.genpos()
TypeError: genpos() missing 1 required positional argument: 'a'

The exception that posted has nothing to do with the try-catch. The control has not even reached the genpos method yet because you're not calling the method properly (missing argument) — rdas
– rdas, Commented Apr 20, 2019 at 8:03
never use bare try except as they catch any exception, even SystemExit or KeyboardInterrupt — Jean-François Fabre
– Jean-François Fabre ♦, Commented Apr 20, 2019 at 8:08
Possible duplicate of How to print Docstring of python function from inside the function itself? — mkrieger1
– mkrieger1, Commented Apr 20, 2019 at 8:11

Alec · Accepted Answer · 2019-04-20 08:04:20Z

0

You can define a new exception:

class CustomError(Exception): pass

raise CustomError('Generate POSCAR : Some error message')

Although, the error you're receiving has nothing to do with the try-except statement. Instead, your gen_pos() function is missing an argument.

answered Apr 20, 2019 at 8:04

Alec

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2 Comments

BaRud Over a year ago

Correct. I am trying to print that docstring when I get such mismatch. Can I do that?

Alec Over a year ago

You can raise whatever message you want

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