[Python] build-in objectに独自のメソッドを追加する禁断の果実

class A:
    pass

A().hello()
# Traceback (most recent call last):
#   File "<stdin>", line 1, in <module>
# AttributeError: 'A' object has no attribute 'hello'

def hello(self):
    print("hello")

setattr(A,'hello',hello)
A().hello()
# hello

setattr(int,'hello',hello)
# Traceback (most recent call last):
#   File "<stdin>", line 1, in <module>
# TypeError: can't set attributes of built-in/extension type 'int'

pip install forbiddenfruit

from forbiddenfruit import curse

def rmspace(self):
    return self.replace(" ", "")

curse(str, "rmspace", rmspace)
print("hello world !".rmspace())

# "helloworld !"

from forbiddenfruit import reverse

reverse(str,"rmspace")

print("hello world !".rmspace())
# Traceback (most recent call last):
#   File "<stdin>", line 1, in <module>
# AttributeError: 'str' object has no attribute 'rmspace'

reverse(str,"split")
"a".split()
# Traceback (most recent call last):
#   File "<stdin>", line 1, in <module>
# AttributeError: 'str' object has no attribute 'split'