How to get a useful exception message from decimal in python 3? - python-3.x

Question

With Python 2, creating a Decimal with an invalid string produces a useful error message:
>>> import decimal
>>> decimal.Decimal('spam')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/decimal.py", line 547, in __new__
"Invalid literal for Decimal: %r" % value)
File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/decimal.py", line 3872, in _raise_error
raise error(explanation)
decimal.InvalidOperation: Invalid literal for Decimal: 'spam'
While Python 3 produces a not-so-helpful message:
>>> import decimal
>>> decimal.Decimal('spam')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
decimal.InvalidOperation: [<class 'decimal.ConversionSyntax'>]
Is there any way to get a useful message like "Invalid literal for Decimal: 'spam'" from the exception in Python 3?
I'm using Python 2.7.15 and Python 3.7.2, both on darwin.
Addenda:
It looks like Python 2 once had a not-very-helpful message for decimal.InvalidOperation: https://bugs.python.org/issue1770009
This situation looks analogous but most of it goes over my head: https://bugs.python.org/issue21227

Answer 1

You could monkey-patch the decimal module.
import decimal
def safe_decimal(something):
try:
funct_holder(something)
except Exception as e:
new_errror = Exception("Hey silly that's not a decimal, what should I do with this? {}".format(something))
raise new_errror from None
funct_holder = decimal.Decimal
decimal.Decimal = safe_decimal
Then you could use the monkey patched version as so
>>> decimal.Decimal('hello')
Traceback (most recent call last):
File "<input>", line 12, in <module>
File "<input>", line 6, in safe_decimal
Exception: Hey silly that's not a decimal, what should I do with this? hello