__rand__() method implements the reverse Bitwise AND * operation with reflected, swapped operands. So, when you call
x * y, Python attempts to call
x.__and__(y). If the method is not implemented, Python attempts to call
__rand__ 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 Bitwise AND &
Python’s bitwise AND operator performs performs logical AND on each bit position on the binary representations of integers
Thus, each output bit is 1 if both input bits at the same position are 1, otherwise, it’s 0.
For example, the integer expression 4 & 3 is translated to binaries 0100 & 0011 which results in 0000 because all four input bit positions are different.
In this example, you apply the bitwise AND operator to two integers 32 and 16:
>>> 32 & 16 0
32 & 16 operates on the bit representations
"010000" (decimal 32) and
"001000" (decimal 16) and performs bitwise AND. As all i-th bit positions are different, the result is 0:
|First Operand ||1||0||0||0||0||0|
|Second Operand ||0||1||0||0||0||0|
To understand this operation in detail, feel free to read over our tutorial or watch the following video:
Python __and__ vs __rand__
Say, you want to calculate the
& operation on two custom objects
print(x & y)
Python first tries to call the left object’s
x.__and__(y). But this may fail for two reasons:
- The method
x.__and__()is not implemented in the first place, or
- The method
x.__and__()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.__rand__() for reverse bitwise AND on the right operand
If the reverse bitwise AND 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.__and__(x) instead of
x.__and__(y), the result would be wrong because the operation may be non-commutative when defined as a custom operation. That’s why
y.__rand__(x) is needed.
So, the difference between
x.__rand__(y) is that the former calculates
x & y whereas the latter calculates
y & x — both calling the respective method defined on the 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 __rand__(self, other): return 'called reverse bitwise AND' x = Data_1() y = Data_2() print(x & y) # called reverse bitwise XOR
Where to Go From Here?
Enough theory. Let’s get some practice!
Coders get paid six figures and more because they can solve problems more effectively using machine intelligence and automation.
To become more successful in coding, solve more real problems for real people. 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?
You build high-value coding skills by working on practical coding projects!
Do you want to stop learning with toy projects and focus on practical code projects that earn you money and solve real problems for people?
🚀 If your answer is YES!, consider becoming 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.
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.