Can you monkey patch methods on core types in Python?
Ruby can add methods to the Number class and other core types to get effects like this:
1.should_equal(1)
But it seems like Python cannot do this. Is this true? And if so, why? Does it have something to do with the fact that type can't be modified?
Update: Rather than talking about different definitions of monkey patching, I would like to just focus on the example above. I have already concluded that it cannot be done as a few of you have answered. But I would like a more detailed explanation of why it cannot be done, and maybe what feature, if available in Python, would allow this.
To answer some of you: The reason I might want to do this is simply aesthetics/readability.
item.price.should_equal(19.99)
This reads more like English and clearly indicates which is the tested value and which is the expected value, as supposed to:
should_equal(item.price, 19.99)
This concept is what Rspec and some other Ruby frameworks are based on.
Answer
No, you cannot. In Python, all data (classes, methods, functions, etc) defined in C extension modules (including builtins) are immutable. This is because C modules are shared between multiple interpreters in the same process, so monkeypatching them would also affect unrelated interpreters in the same process. (Multiple interpreters in the same process are possible through the C API, and there has been some effort towards making them usable at Python level.)
However, classes defined in Python code may be monkeypatched because they are local to that interpreter.