The second 'key in dict' option is not thread safe if dict_ is not local (another thread may delete the entry between the existence check and use). This is a go

The second 'key in dict' option is not thread safe if dict_ is not local (another thread may delete the entry between the existence check and use). This is a good reason why the exception handling approach is a better idiom. The exception handling approach may also be faster if your code cares (may, because I don't know if the cost of calculating the hash of "key" twice is cheaper than the exception handling overhead).