create chain methods for class in python

Question

Let's say I have the following class:

class MyClass: 
    def __init__(self, text):
        self.text = text

    def strip(self):
        strip_text = self.text.strip()

        return strip_text

    def reverse(self):
        rev_text = self.text.strip()[::-1]

        return rev_text

my_name = MyClass('todd ')

I want to able to to call the methods to this class like this:

my_name.strip().reverse()

However, when I do so, it throws an error. How do I go about chaining methods?

you need to return self so be able to chain operations, so instead of returning strip_text, set self.strip_text = strip_text and return self — Bernardo stearns reisen, Apr 29 '20 at 19:16
This is called a *fluent interface*. Not as common in Python, although some third-party libraries use it. See [this](https://stackoverflow.com/questions/43380042/purpose-of-return-self-python/43380360#43380360) — juanpa.arrivillaga, Apr 29 '20 at 19:17
_it throws an error_ Seeing the error would help a lot in tracking down the problem. — John Gordon, Apr 29 '20 at 19:17
Does this answer your question? [Purpose of return self python](https://stackoverflow.com/questions/43380042/purpose-of-return-self-python) — Bernardo stearns reisen, Apr 29 '20 at 19:18
`my_name.strip()` returns an ordinary string, which does not have a `.reverse()` method. — John Gordon, Apr 29 '20 at 19:19
When you get to `reverse`, I think the error is because `my_name.strip()` becomes a `String`, not part of your `Class` — BruceWayne, Apr 29 '20 at 19:20

score 1 · Answer 1 · answered Apr 29 '20 at 19:21

my_name.strip() returns a String, which has no reverse() function.

A quick way is just to make my_name.strip() a new Class object, and reverse that:

MyClass(my_name.strip()).reverse()

_{(However, IMO this is kludgy and there's a better (more pythonic) way to fix this in the Class definition(s) itself.)}

score 0 · Answer 2 · answered Apr 29 '20 at 19:35

Each function has to replace the wrapped string, then return self. At the end of the chain, you retrieve the final result.

class MyClass: 
    def __init__(self, text):
        self.text = text

    def strip(self):
        self.text = self.text.strip()

        return self

    def reverse(self):
        self.text = self.text.strip()[::-1]

        return self


my_name.strip().reverse().text

As an alternative to mutating the existing object, a new instance can be returned at each step.

class MyClass: 
    def __init__(self, text):
        self.text = text

    def strip(self):
        return MyClass(self.text.strip())

    def reverse(self):
        return MyClass(self.text.strip()[::-1])

create chain methods for class in python

2 Answers2