Python try except - Include the custom message in the Error variable

Question

Im trying to do a simple try except, and it is working. But I want to add some custom string at the beginning of the error message. If I just add it in print, its giving error.

import sys

try:
    with open('./datatype-mapping/file.json') as rs_mapping:
         data_mapping = json.load(rs_mapping)
except Exception as error:
        print('CUSTOM ERROR: '+error)
        sys.exit(1)

The error I got is,

Traceback (most recent call last):
  File "c:/Users/rbhuv/Desktop/code/bqshift.py", line 22, in get_datatype_mapping
    with open('./datatype-mapping/file.json') as rs_mapping:
FileNotFoundError: [Errno 2] No such file or directory: './datatype-mapping/file.json'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "c:/Users/rbhuv/Desktop/code/bqshift.py", line 102, in <module>
    main()
  File "c:/Users/rbhuv/Desktop/code/bqshift.py", line 99, in main
    target_mapping()
  File "c:/Users/rbhuv/Desktop/code/bqshift.py", line 39, in target_mapping
    data_mapping = get_datatype_mapping()
  File "c:/Users/rbhuv/Desktop/code/bqshift.py", line 26, in get_datatype_mapping
    print('ERROR: '+error)
TypeError: can only concatenate str (not "FileNotFoundError") to str

But if I use just print(error) - this is working.

Python doesn't have a concept of type-coercion, this why concatenating a Exception to a str doesn't make a Exception turn into a string. — tripulse
– tripulse, Commented Aug 3, 2020 at 6:34

s d · Accepted Answer · 2020-08-03 03:17:26Z

2

You need to convert error to str.

import sys

try:
  int("fail")
except Exception as error:
  print('CUSTOM ERROR: ' + str(error))
  sys.exit(1)

This works flawlessly.

answered Aug 3, 2020 at 3:17

s d

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