How to suppress displaying the parent exception (the cause) for subsequent exceptions

Question

I\'m aware of raise ... from None and have read How can I more easily suppress previous exceptions when I raise my own exception in response?.

However,

Answer 1

You have a few options here.

First, a cleaner version of what orlp suggested:

try:
    value = cache_dict[key]
except KeyError:
    try:
        value = some_api.get_the_value(key)
    except Exception as e:
        raise e from None
    cache_dict[key] = value

For the second option, I'm assuming there's a return value hiding in there somewhere that you're not showing:

try:
    return cache_dict[key]
except KeyError:
    pass
value = cache_dict[key] = some_api.get_the_value(key)
return value

Third option, LBYL:

if key not in cache_dict:
    cache_dict[key] = some_api.get_the_value(key)
return cache_dict[key]

For the bonus question, define your own dict subclass that defines __missing__:

class MyCacheDict(dict):

    def __missing__(self, key):
        value = self[key] = some_api.get_the_value(key)
        return value

Hope this helps!

Answer 2

You can try suppressing the context yourself:

try:
    value = cache_dict[key]
except KeyError:
    try:
        value = some_api.get_the_value_via_web_service_call(key)
    except Exception as e:
        e.__context__ = None
        raise

    cache_dict[key] = value