Computers store all kinds of information as a stream of binary digits called bits. Whether you’re working with text, images, or videos, they all boil down to ones and zeros. Python’s bitwise operators let you manipulate those individual bits of data at the most granular level.
You can use bitwise operators to implement algorithms such as compression, encryption, and error detection as well as to control physical devices in your Raspberry Pi project or elsewhere. Often, Python isolates you from the underlying bits with high-level abstractions. You’re more likely to find the overloaded flavors of bitwise operators in practice. But when you work with them in their original form, you’ll be surprised by their quirks!
In this tutorial, you’ll learn how to:
- Use Python bitwise operators to manipulate individual bits
- Read and write binary data in a platform-agnostic way
- Use bitmasks to pack information on a single byte
- Overload Python bitwise operators in custom data types
- Hide secret messages in digital images
To get the complete source code of the digital watermarking example, and to extract a secret treat hidden in an image, click the link below:
Get the Source Code: Click here to get the source code you’ll use to learn about Python’s bitwise operators in this tutorial.
Overview of Python’s Bitwise Operators
Python comes with a few different kinds of operators, such as the arithmetic, logical, and comparison operators. You can think of them as functions that take advantage of a more compact prefix and infix syntax.
Note: Python does not include postfix operators like the increment (i++) or decrement (i--) operators available in C.
Bitwise operators look virtually the same across different programming languages:
| Operator | Example | Meaning |
|---|---|---|
& |
a & b |
Bitwise AND |
| |
a | b |
Bitwise OR |
^ |
a ^ b |
Bitwise XOR (exclusive OR) |
~ |
~a |
Bitwise NOT |
<< |
a << n |
Bitwise left shift |
>> |
a >> n |
Bitwise right shift |
As you can see, they’re denoted with strange-looking symbols instead of words. This makes them stand out in Python as slightly less verbose than you might be used to seeing. You probably wouldn’t be able to figure out their meaning just by looking at them.
Note: If you’re coming from another programming language such as Java, then you’ll immediately notice that Python is missing the unsigned right shift operator denoted by three greater-than signs (>>>).
This has to do with how Python represents integers internally. Since integers in Python can have an infinite number of bits, the sign bit doesn’t have a fixed position. In fact, there’s no sign bit at all in Python!
Most of the bitwise operators are binary, which means that they expect two operands to work with, typically referred to as the left operand and the right operand. Bitwise NOT (~) is the only unary bitwise operator since it expects just one operand.
All binary bitwise operators have a corresponding compound operator that performs an augmented assignment:
| Operator | Example | Equivalent to |
|---|---|---|
&= |
a &= b |
a = a & b |
|= |
a |= b |
a = a | b |
^= |
a ^= b |
a = a ^ b |
<<= |
a <<= n |
a = a << n |
>>= |
a >>= n |
a = a >> n |
These are shorthand notations for updating the left operand in place.
That’s all there is to Python’s bitwise operator syntax! Now you’re ready to take a closer look at each of the operators to understand where they’re most useful and how you can use them. First, you’ll get a quick refresher on the binary system before looking at two categories of bitwise operators: the bitwise logical operators and the bitwise shift operators.
Binary System in Five Minutes
Before moving on, take a moment to brush up your knowledge of the binary system, which is essential to understanding bitwise operators. If you’re already comfortable with it, then go ahead and jump to the Bitwise Logical Operators section below.
Why Use Binary?
There are an infinite number of ways to represent numbers. Since ancient times, people have developed different notations, such as Roman numerals and Egyptian hieroglyphs. Most modern civilizations use positional notation, which is efficient, flexible, and well suited for doing arithmetic.
A notable feature of any positional system is its base, which represents the number of digits available. People naturally favor the base-ten numeral system, also known as the decimal system, because it plays nicely with counting on fingers.
Computers, on the other hand, treat data as a bunch of numbers expressed in the base-two numeral system, more commonly known as the binary system. Such numbers are composed of only two digits, zero and one.
Note: In math books, the base of a numeric literal is commonly denoted with a subscript that appears slightly below the baseline, such as 4210.
Read the full article at https://realpython.com/python-bitwise-operators/ »
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