+ 6

Can a python class delegate to another class?

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?

17th Jul 2021, 11:19 AM
Oma Falk
Oma Falk - avatar
20 odpowiedzi
+ 5
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
18th Jul 2021, 9:34 AM
michal
+ 4
https://code.sololearn.com/cuaZYJwGUPDb/?ref=app
18th Jul 2021, 1:24 PM
Vitaly Sokol
Vitaly Sokol - avatar
+ 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!
20th Jul 2021, 8:14 PM
Tibor Santa
Tibor Santa - avatar
+ 3
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/
18th Jul 2021, 5:14 AM
David Carroll
David Carroll - avatar
+ 2
Oma Falk I didn't understand your question. Did you mean to totally mask the str class with another name?
17th Jul 2021, 8:32 PM
Calvin Thomas
Calvin Thomas - avatar
+ 2
Zen Coding yes...seens to be the only
18th Jul 2021, 6:53 AM
Oma Falk
Oma Falk - avatar
+ 1
Calvin Thomas yes mystring inherits from str, redefines and adds some methods and after I hoped for str. delegate(mystring)
18th Jul 2021, 4:46 AM
Oma Falk
Oma Falk - avatar
+ 1
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.
18th Jul 2021, 5:23 AM
Oma Falk
Oma Falk - avatar
+ 1
Oma Falk This does the job I guess: str = mystring
18th Jul 2021, 6:17 AM
Calvin Thomas
Calvin Thomas - avatar
+ 1
Calvin Thomas I guessed too but😢😢
18th Jul 2021, 6:18 AM
Oma Falk
Oma Falk - avatar
+ 1
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()?
18th Jul 2021, 6:42 AM
Zen Coding
Zen Coding - avatar
+ 1
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.
18th Jul 2021, 6:45 AM
Zen Coding
Zen Coding - avatar
0
I doped that works. You could probably shadow 'str' by your class but probably only in a limited scope
17th Jul 2021, 11:25 AM
Zen Coding
Zen Coding - avatar
0
Zen Coding ohhh it goes deeeeep into Cpython. BUT...nice!😈😈😈
17th Jul 2021, 11:52 AM
Oma Falk
Oma Falk - avatar
0
Oma Falk Did you mean this: class newString(str): def foo(self, x): print(x) # TEST str = newString("FOO")
18th Jul 2021, 4:50 AM
Calvin Thomas
Calvin Thomas - avatar
0
Oma Falk What had gone wrong? A better explanation helps.
18th Jul 2021, 6:26 AM
Calvin Thomas
Calvin Thomas - avatar
0
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.
18th Jul 2021, 8:40 AM
Calvin Thomas
Calvin Thomas - avatar
0
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.
18th Jul 2021, 8:44 AM
Calvin Thomas
Calvin Thomas - avatar