Can a python class delegate to another class?

Question

Lets say we have the built_in class str.
We say

def class mystring(str):
...

Now in my special prog standard strings shall behave like mystring.
Is it possible?

Answer 1

Does that help? https://stackoverflow.com/questions/6738987/extension-method-for-JUMP_LINK__&&__python__&&__JUMP_LINK-built-in-types

Answer 2

This is the closest I could get.
I use the unittest.mock library. But you need to wrap your string into str(...) for it to take effect.
https://code.sololearn.com/cA0A5a12A8a3/?ref=app

Answer 3

https://code.sololearn.com/cuaZYJwGUPDb/?ref=app

Answer 4

https://code.sololearn.com/cA51a20A9A7a/?ref=app

Forbiddenfruit does really work nicely 😁
Zen Coding thank you for the highlight!

But it is really a double-edged sword, the more methods you want to override, you will be in a difficult position because you are not allowed to use in the implementation those methods that were changed to bogus!

Answer 5

Oma Falk Can you provide more clarification or a specific use case of what you mean by:

str.delegate(subclassOfString)

Are you using that method name generically or is it meant to refer to a design pattern?
Perhaps, this link is what you're looking for.

https://programmingideaswithjake.wordpress.com/2015/05/23/JUMP_LINK__&&__python__&&__JUMP_LINK-decorator-for-simplifying-delegate-pattern/

Answer 6

Oma Falk I didn't understand your question. Did you mean to totally mask the str class with another name?

Answer 7

Calvin Thomas

https://code.sololearn.com/c1Gf3oP7C9kq/?ref=app

Answer 8

Zen Coding yes...seens to be the only

Answer 9

Calvin Thomas
yes mystring inherits from str, redefines and adds some methods and after I hoped for
str. delegate(mystring)

Answer 10

David Carroll

str.delegate(mystring) means whenever a method m of object str is called, the real call is mystring.m()

Since mystring inherits from str, the call is save.

Str and mystring is an example, it counts for all objects and their children.

Answer 11

Oma Falk This does the job I guess:

str = mystring

Answer 12

Calvin Thomas I guessed too but😢😢

Answer 13

Calvin Thomas I am not sure, if that works.

Let's say you have your own split method in mystring.

str = mystring
"Blub". split('/')

Would the second line call mystring.split()?

Answer 14

Oma Falk In my stackoverflow the solution uses a library called forbiddenfruit. https://pypi.org/project/forbiddenfruit/

I think that is close to what you want.

Answer 15

I doped that works. You could probably shadow 'str' by your class but probably only in a limited scope

Answer 16

Zen Coding ohhh it goes deeeeep into Cpython.
BUT...nice!😈😈😈

Answer 17

Oma Falk Did you mean this:

class newString(str):
def foo(self, x):
print(x)
# TEST

str = newString("FOO")

Answer 18

Oma Falk What had gone wrong? A better explanation helps.

Answer 19

Zen Coding and Oma Falk I guess that Python was designed to consider anything surrounded by quotes as a string object, regardless of the external variable 'str'. The actual class isn't cleared from the heap even though the reference is lost. This is a built-in functionality, I guess.

Answer 20

I don't know what's happening here:

del __builtins__.str
print(type("a"))

P.S. David Carroll Would love to receive some help on this matter.