Five Steps to Access and Format Exception Objects in Python

The aim of this page📝is to outline 5 steps for accessing exception objects and formatting their content. From the great Core Python course on Pluralsight.

1. five steps

1. import sys at the top of your script
2. use as clause at the end of the except statement and create an alias for the error object (e.g. e)
3. print error message with an f string
4. use f"{e!r}" inserting the repl representation into your strings. In case of exception objects, this gives us more info about the type of the exception
5. pass a keyword argument file=sys.stderr into the print statement

2. example

import sys          #1
DIGIT_MAP = {
    'zero': '0',
    'one': '1',
    'two': '2',
    'three': '3',
    'four': '4',
    'five': '5',
    'six': '6',
    'seven': '7',
    'eight': '8',
    'nine': '9',
}
def convert(s):
    number = ''
    x = -1
    try:
        for token in s:
            number += DIGIT_MAP[token]
        x = int(number)
        print(f"Conversion Succeded. x = {x}")
    except (KeyError, TypeError) as e:          #2
        print(f"{e!r}", file=sys.stderr)        #3-5
    return x
print(convert(512)

• this returns

TypeError("'int' object is not iterable")
-1