__truediv__() method is called to implement the normal division operation
/ called true division—as opposed to the floor division operation
//. For example to evaluate the expression
x / y, Python attempts to call
We call this a “Dunder Method” for “Double Underscore Method” (also called “magic method”). To get a list of all dunder methods with explanation, check out our dunder cheat sheet article on this blog.
In the following example, you create a custom class
Data and overwrite the
__truediv__() method so that it returns a dummy string when trying to divide two
Data objects using the true division operation
a / b.
class Data: def __truediv__(self, other): return '... my result of truediv...' a = Data() b = Data() c = a / b print(c) # ... my result of truediv...
If you hadn’t defined the
__truediv__() method, Python would’ve raised a
How to Resolve TypeError: unsupported operand type(s) for /
Consider the following code snippet where you try to divide two custom objects without defining the dunder method
class Data: pass a = Data() b = Data() c = a / b print(c)
Running this leads to the following error message on my computer:
Traceback (most recent call last): File "C:\Users\xcent\Desktop\code.py", line 7, in <module> c = a / b TypeError: unsupported operand type(s) for /: 'Data' and 'Data'
The reason for this error is that the
__truediv__() dunder method has never been defined—and it is not defined for a custom object by default. So, to resolve the
TypeError: unsupported operand type(s) for /, you need to provide the
__truediv__(self, other) method in your class definition as shown previously:
class Data: def __truediv__(self, other): return '... my result of truediv...'
Python __truediv__ vs __div__
- The Python
__truediv__()dunder method is called to implement the normal division operation in Python 3.
- The Python
__div__() dunder method is called to implement the normal division operation in Python 2. It doesn’t work in Python 3 anymore.
Python __truediv__ vs __rtruediv__
Say, you want to divide two objects
y using true division:
print(x / y)
Python first tries to call the left object’s
x.__truediv__(y). But this may fail for two reasons:
- The method
x.__truediv__()is not implemented in the first place, or
- The method
x.__truediv__()is implemented but returns a
NotImplementedvalue indicating that the data types are incompatible.
If this fails, Python tries to fix it by calling the
y.__rtruediv__() for reverse true division on the right operator
y. If this method is implemented, Python knows that it doesn’t run into a potential problem of a non-commutative operation. If it would just execute
y.__truediv__(x) instead of
x.__truediv__(y), it could cause an error if the operation is non-commutative. That’s why
y.__rtruediv__(x) is needed which indicates that true division is possible after all.
So, the difference between
x.__rtruediv__(y) is that the former calculates
x / y whereas the latter calculates
y / x — both calling the respective true division method defined on object
Explainer Video Division Operators
You can also check out my explainer video where I’ll give you a deep dive on the integer and true division operators and how to use them for various data types. Click to watch:
Where to Go From Here?
Enough theory, let’s get some practice!
To become successful in coding, you need to get out there and solve real problems for real people. That’s how you can become a six-figure earner easily. And that’s how you polish the skills you really need in practice. After all, what’s the use of learning theory that nobody ever needs?
Practice projects is how you sharpen your saw in coding!
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Then become a Python freelance developer! It’s the best way of approaching the task of improving your Python skills—even if you are a complete beginner.
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While working as a researcher in distributed systems, Dr. Christian Mayer found his love for teaching computer science students.
To help students reach higher levels of Python success, he founded the programming education website Finxter.com. He’s author of the popular programming book Python One-Liners (NoStarch 2020), coauthor of the Coffee Break Python series of self-published books, computer science enthusiast, freelancer, and owner of one of the top 10 largest Python blogs worldwide.
His passions are writing, reading, and coding. But his greatest passion is to serve aspiring coders through Finxter and help them to boost their skills. You can join his free email academy here.