Monkey Patching a String Python

Question

I am working on a python project and below is what I have:

mystring= 'Hello work'

and I want to write a function that replaces k with a m some thing like below:

def replace_alpha(string):
    return string.replace('k', 'm') # returns Hello worm

I wanted to use Monkey Patching on a string such that I can use it the below way:

string = 'Hello work'
string = string.replace_alpha()
print(string)   # prints Hello worm

instead of:

string = replace_alpha(string)

is this possible? Can I use monkey patching with a built-in rather can I extent the __builtins__?

That's not monkey patching. Monkey patching is the modification of an object from a different scope. — Klaus D., Oct 25 '18 at 07:37
@hspandher op stated that he doesnt want to touch `__builtins__`. — georgexsh, Oct 25 '18 at 07:48

score 4 · Accepted Answer · answered Oct 25 '18 at 07:42

4

It is possible with forbiddenfruit library:

from forbiddenfruit import curse

def replace_alpha(string):
    return string.replace('k', 'm')

curse(str, "replace_alpha", replace_alpha)

s = 'Hello work'
print(s.replace_alpha())

answered Oct 25 '18 at 07:42

georgexsh

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The wording of this library is beautiful :) – Erik Brendel Dec 08 '21 at 12:38

user2390182 · Answer 2 · 2018-10-25T07:43:54.900

1

It is not possible so easily. You cannot set attributes of immutable str instances or the built-in str class. Without that capability, it is tough change their behaviour. You can, however, subclass str:

class PatchStr(str):
  def replace_alpha(self):
    return self.replace('k', 'm')

string = PatchStr('hello work')
string = string.replace_alpha()
string
# 'hello worm'

I don't think you can get much closer.

edited Oct 25 '18 at 07:43

answered Oct 25 '18 at 07:41

user2390182

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`string` remains `"hello work"`, however. – Adam Smith Oct 25 '18 at 07:41
@AdamSmith which it (the str object the method is called on) does in the OP's code, too. Of course, you have to reassign the return value. – user2390182 Oct 25 '18 at 07:43
That's not how I understand the requested end state. – Adam Smith Oct 25 '18 at 07:44
2

@AdamSmith `string` is just a variable name. The behaviour is the one stated by the OP. `string = string.replace_alpha()` in the original post indicates that they are not expecting to mutate the object. – user2390182 Oct 25 '18 at 07:46

Monkey Patching a String Python

2 Answers2