__rdivmod__() method implements the
divmod() built-in function with reflected, swapped operands. So, when you call
divmod(x, y), Python attempts to call
x.__divmod__(y). If the method is not implemented, Python attempts to call
__rdivmod__ on the right operand. Only 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.
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
- 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:
What’s the Difference Between __divmod__() and __rdivmod__()?
Say, you want to apply the
divmod() function to two 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 operator
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), it could cause an error if the operation is non-commutative. That’s why
y.__rdivmod__(x) is needed.
The difference between
x.__rdivmod__(y) is that the former calculates
divmod(x, y) whereas the latter calculates
divmod(y, x) — both calling it on object
You can see this in effect here where we attempt to call the operation on the left operand
x—but as it’s not implemented, Python simply calls the reverse operation on the right operand
class Data_1: pass class Data_2: def __rdivmod__(self, other): return 'called reverse divmod' x = Data_1() y = Data_2() print(divmod(x, y)) # called reverse divmod
Where to Go From Here?
Enough theory. Let’s get some practice!
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If you just want to learn about the freelancing opportunity, feel free to watch my free webinar “How to Build Your High-Income Skill Python” and learn how I grew my coding business online and how you can, too—from the comfort of your own home.
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.