CODEWITHSUNDEEP
pythonexception
Gregory Hassett
Gregory Hassett

Reputation: 346

Exception decimal.ConversionSyntax not caught

This appears to be a simple Python question but it's got me scratching my head. I would expect the following code to print "Caught [<class 'decimal.ConversionSyntax'>]".

Instead of the specific except decimal.ConversionSyntax exception handler being called, it falls through to the generic except Exception as ex and prints out "Exception [<class 'decimal.ConversionSyntax'>] not caught in previous except clause".

Am I missing something obvious? Appreciate any insights -- thanks!

import decimal

amount = 'this is not a valid decimal string'

try:
    amount = decimal.Decimal(amount).quantize(decimal.Decimal('.01'))
except decimal.ConversionSyntax as cex:
    print(f'Caught {cex}')
except Exception as ex:
    print(f'Exception {ex} not caught in previous except clause')

Running the code:

$ python3 /tmp/decimal-exception.py 
Exception [<class 'decimal.ConversionSyntax'>] not caught in previous except clause

Upvotes: 0

Views: 1436

Answers (1)

Karl Knechtel
Karl Knechtel

Reputation: 61519

Some diagnostics:

>>> try:
...   decimal.Decimal(amount)
... except Exception as e:
...   f = e
...
>>> f
InvalidOperation([<class 'decimal.ConversionSyntax'>])
>>> f.__class__
<class 'decimal.InvalidOperation'>

decimal.InvalidOperation is the class you should actually be looking for. Even though the string representation of the exception mentions decimal.ConversionSyntax, and that is indeed a subclass of decimal.InvalidOperation, the base class is raised.

Upvotes: 1

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