How can I modify the code to achieve the effect of python pass by reference, so that the output is "Changed"?

General Discussions
1

I wrote this class for testing:

class PassByReference:
    def __init__(self):
        self.variable = 'Original'
        self.change(self.variable)
        print(self.variable)

    def change(self, var):
        var = 'Changed'

When I created an instance, the output was “Original.” So, it seems like parameters in Python are passed by value. Is that correct? How can I modify the code to achieve the effect of Python pass-by reference so that the output is “Changed”?

2

Since Python passes immutable types (like strings) by value, you can use a mutable object, such as a list or dictionary, to simulate passing by reference.

Here’s an example using a list:

class PassByReference:
    def __init__(self):
        self.variable = ['Original']  # Use a list (mutable)
        self.change(self.variable)
        print(self.variable[0])  # Access the first element

    def change(self, var):
        var[0] = 'Changed'  # Modify the list's content

In this solution, the list variable is mutable, so when it’s passed to change, the changes affect the original list. This is an example of a Python pass-by reference with a mutable object.

3

Another way to simulate Python pass by reference is by using a dictionary, which is also mutable:

class PassByReference:
    def __init__(self):
        self.variable = {'value': 'Original'}  # Use a dictionary (mutable)
        self.change(self.variable)
        print(self.variable['value'])  # Access the dictionary value

    def change(self, var):
        var['value'] = 'Changed'  # Modify the dictionary's value

With this solution, the dictionary’s value can be modified inside the change method, and the change is reflected in the original object.

4

You can create a custom object that holds the value and pass that object to simulate Python pass-by reference:

class PassByReference:
    def __init__(self):
        self.variable = MyVariable('Original')  # Pass a custom object
        self.change(self.variable)
        print(self.variable.value)  # Access the object's attribute

    def change(self, var):
        var.value = 'Changed'  # Modify the attribute of the object

class MyVariable:
    def __init__(self, value):
        self.value = value

Here, MyVariable is a custom class with an attribute value. When the variable object is passed to change, its value attribute can be modified directly, simulating Python pass-by reference.