Patch for str __add__ not working

[Liu Peng]

I want to modify __add__ magic function for str, but somehow it is not working. Refer to a previous issue #21, the code below is working fine:

from forbiddenfruit import curse

def __add__(self, a):
    """
        this is the test
    """
    if isinstance(a, bytes):
        self += a.decode('utf-8')
    else:
        self += a


curse(str, '__add__', __add__)

s = "sample string"a
print(s + "encode string".encode('utf-8'))

However, I discovered that if you try to do "a" + "b" instead of "a" + b"b", the modified function is not called (I tried to print something out inside the new __add__ function). It turns out the modified function only works when the type of the second variable is not str.

Any idea why this happens? By the way, I tried on Python 3.8.10