OOP Coding Style – Should Everything Be Initialized in the Constructor?

I still consider myself as an apprentice programmer, so I'm always looking to learn a "better" way for typical programming. Today, my coworker has argued that my coding style does some unnecessary work, and I want to hear opinions from others.
Typically, when I design a class in OOP language (Usually C++ or Python), I would separate the initialization into two different parts:

class MyClass1 {
public:
    Myclass1(type1 arg1, type2 arg2, type3 arg3);
    initMyClass1();
private:
    type1 param1;
    type2 param2;
    type3 param3;
    type4 anotherParam1;
};

// Only the direct assignments from the input arguments are done in the constructor
MyClass1::myClass1(type1 arg1, type2 arg2, type3 arg3)
    : param1(arg1)
    , param2(arg2)
    , param3(arg3)
    {}

// Any other procedure is done in a separate initialization function 
MyClass1::initMyClass1() {
    // Validate input arguments before calculations
    if (checkInputs()) {
    // Do some calculations here to figure out the value of anotherParam1
        anotherParam1 = someCalculation();
    } else {
        printf("Something went wrong!\n");
        ASSERT(FALSE)
    }
}

(or, python equivalent)

class MyClass1:

    def __init__(self, arg1, arg2, arg3):
        self.arg1 = arg1
        self.arg2 = arg2
        self.arg3 = arg3
        #optional
        self.anotherParam1 = None

    def initMyClass1():
        if checkInputs():
            anotherParam1 = someCalculation()
        else:
            raise "Something went wrong!"

What is your opinion about this approach? Should I refrain from splitting the initialization process? The question is not only limited to C++ and Python, and answers for other languages are also appreciated.