__divmod__() method implements the built-in divmod operation. So, when you call
divmod(a, b), Python attempts to call
x.__divmod__(y). If the method is not implemented, Python first attempts to call
__rdivmod__ on the right operand and if this isn’t implemented either, it raises a
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.
Background Default divmod()
divmod(a, b) function takes two integer or float numbers
b as input arguments and returns a tuple
(a // b, a % b). The first tuple value is the result of the integer division
a//b. The second tuple is the result of the remainder, also called modulo operation
a % b. In case of float inputs,
divmod() still returns the division without remainder by rounding down to the next round number.
To understand this operation in detail, feel free to read over our tutorial or watch the following video:
Example Custom divmod()
In the following example, you create a custom class
Data and overwrite the
__divmod__() method so that it returns a dummy string when trying to calculate the modulo of two numbers.
class Data: def __divmod__(self, other): return '... my result of divmod...' a = Data() b = Data() c = divmod(a, b) print(c) # ... my result of divmod...
If you hadn’t defined the
__divmod__() method, Python would’ve raised a
How to Resolve TypeError: unsupported operand type(s) for divmod()
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 = divmod(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 = divmod(a, b) TypeError: unsupported operand type(s) for divmod(): 'Data' and 'Data'
The reason for this error is that the
__divmod__() 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 divmod(), you need to provide the
__divmod__(self, other) method in your class definition as shown previously:
class Data: def __divmod__(self, other): return '... my result of divmod...'
Of course, you’d use another return value in practice as explained in the “Background divmod()” section.
Python __divmod__ vs __rdivmod__
Say, you want to calculate the divmod of two custom objects
Python first tries to call the left object’s
x.__divmod__(y). But this may fail for two reasons:
- The method
x.__divmod__()is not implemented in the first place, or
- The method
x.__divmod__()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.__rdivmod__() for reverse divmod on the right operand
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.__divmod__(x) instead of
x.__divmod__(y), the result would be wrong because the divmod operation is non-commutative (neither the integer division, nor the modulo operation is commutative). That’s why
y.__rdivmod__(x) is needed.
So, the difference between
x.__rdivmod__(y) is that the former calculates
(x // y, x % y) whereas the latter calculates
(y // x, y % x) — both calling the respective divmod method defined on object
You can see this in effect here where we attempt to call the divmod operation on the left operand
x—but as it’s not implemented, Python simply calls the reverse divmod operation on the right operand
class Data_1: pass class Data_2: def __rdivmod__(self, other): return 'called divmod' x = Data_1() y = Data_2() print(divmod(x, y)) # called divmod
Explainer Video Modulo
You can also check out my explainer video where I’ll give you a deep dive on the built-in modulo operation and how to use them for various data types. Click to watch:
Where to Go From Here?
Enough theory. Let’s get some practice!
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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 that has taught exponential skills to millions of coders worldwide. He’s the author of the best-selling programming books Python One-Liners (NoStarch 2020), The Art of Clean Code (NoStarch 2022), and The Book of Dash (NoStarch 2022). Chris also coauthored the Coffee Break Python series of self-published books. He’s a 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.