When trying to serialise an unsupported object type to bson, the error message that pymongo generates is sometimes very unhelpful.

For example, I was trying to save a document like this:

{
  "value": number1 < number2
}

Normally this would result in a bool, which would be fine.

However, this is the error message I get when trying to run this:

InvalidDocument: Cannot encode object: True

You may ask why it cannot serialise a bool.

It turns out that number1 can sometimes be a numpy type. As a result, the type of the comparison is actually `numpy.bool_` instead of a standard python bool.

The error message would be much more helpful if it contained the type() of the object. For example:

InvalidDocument: Cannot encode object of type 'numpy.bool_': True