5 Best Ways to Change the Real Part of the Complex Argument in Python

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πŸ’‘ Problem Formulation: How can one modify the real part of a complex number in Python without altering its imaginary part? Imagine we have a complex number 3+4j and we want to change the real part to 9, resulting in a new complex number 9+4j.

Method 1: Using the complex() Constructor

This method utilizes Python’s built-in complex(real, imag) function to construct a new complex number with a specified real component. By providing the desired real part and the imaginary part of the original complex number, one can create the modified complex number. This approach is clean and straightforward.

Here’s an example:

original_num = 3 + 4j
new_real = 9
new_num = complex(new_real, original_num.imag)

Output: 9+4j

The code snippet creates a new complex number by explicitly setting the real part to 9 while preserving the imaginary part from the original number, original_num.imag.

Method 2: Addition and Subtraction

A mathematical solution is to subtract the original real part and then add the new real part. This is a bit more convoluted and relies on the arithmetic operation overloads in the Python complex number implementation. It guarantees the preservation of the original number’s imaginary part.

Here’s an example:

original_num = 3 + 4j
new_real = 9
new_num = original_num - original_num.real + new_real

Output: 9+4j

The snippet works by first subtracting the original real part then adding the desired new real part. Both operations are done in the context of complex arithmetic.

Method 3: Using a Custom Function

Defining a custom function can provide a reusable solution for changing the real part of a complex number. This method encapsulates the process into a simple function call, increasing code readability and maintainability when the operation is needed multiple times.

Here’s an example:

def change_real(complex_num, new_real):
    return complex(new_real, complex_num.imag)

original_num = 3 + 4j
new_num = change_real(original_num, 9)

Output: 9+4j

The change_real() function allows for changing the real part of the given complex number to any provided real value while keeping the imaginary part intact.

Method 4: Object Oriented Approach

Python’s object-oriented capabilities let you wrap the operation in a class that represents a complex number. This method offers a clear structure, especially in a larger system where complex numbers are frequently manipulated.

Here’s an example:

class MyComplexNumber:
    def __init__(self, real, imag):
        self.real = real
        self.imag = imag
    def set_real(self, new_real):
        self.real = new_real
    def __repr__(self):
        return f"{self.real}+{self.imag}j"

number = MyComplexNumber(3, 4)

Output: 9+4j

Here, the MyComplexNumber class defines a complex number, and changing the real part is as simple as calling the set_real() method on an instance.

Bonus One-Liner Method 5: Tuple Unpacking

Python’s tuple unpacking feature can be cleverly used for this purpose. You create a tuple of the new real part and the existing imaginary part, and then convert it to a complex number. It is a concise one-liner fix but lacks some readability for those unfamiliar with Python’s tuple capabilities.

Here’s an example:

original_num = 3 + 4j
new_real = 9
new_num = complex(*(new_real, original_num.imag))

Output: 9+4j

The provided code uses tuple unpacking inside the complex() constructor to form a new complex number with the updated real part.


  • Method 1: Using the complex() Constructor. Simple and direct. Does not modify the original number.
  • Method 2: Addition and Subtraction. Relies on arithmetic operations. Can be less clear to understand at a glance.
  • Method 3: Using a Custom Function. Encapsulates logic into a function. Increases code modularity, but adds an extra function definition.
  • Method 4: Object Oriented Approach. Wraps the complex number in a class structure. Ideal for systems with numerous complex number manipulations, could be overkill for simple tasks.
  • Method 5: Tuple Unpacking. Provides a one-liner solution. Clever use of Python’s unpacking, but may be confusing for beginners.