Python equal operator, avoid bugs of type: (<string> == <number>) -> False

Question

Is there a way to obtain an exception when the == (equal) operator is used to compare different types? Python 3 throws an exception when attempting to order objects of different types. But == still returns False.

Or is there some other way to avoid hard to detect bugs caused by wrong type assumptions? Are there any design-patterns that could help?

I'm thinking of, e.g., a case where someone uses someone elses implementation of xmlparser.get() which always returns a string, even if the property is basically a number.

Answer 1

No. Because for ==, the reasoning is that equality implies comparibility. If two objects aren't even comparable they are not equal, therefore it will return false and never throw an exception.

Answer 2

No, python is inherently dynamically typed.

If you must doublecheck a type, use the isinstance() function, or use duck typing to test for specific behaviour.

Answer 3

I'm thinking of, e.g., a case where someone uses someone elses implementation of xmlparser.get() which always returns a string, even if the property is basically a number.

You might want to coerce the value to a number by calling int or float on it, as appropriate.

Answer 4

Despite the fact that Python has dynamic typing, it is strong (not duck). So:

>>> 42 == 42
True
>>> 42 == 42.0
True
>>> 42 == "42"
False
>>> 42 == int("42")
True

You have to perform an explicit type conversion when getting a string representation of the number.

On the other hand, you can manage comparison of your custom objects by defining methods __eq__(self, other) or __cmp__(self, other) in your class.