Python Bytecode Instructions

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Alright ! Let’s talk about something that might make your eyes glaze over faster than a PowerPoint presentation on tax reform: bytecode instructions in Python. But don’t worry we won’t get too technical here, we’ll keep it light and breezy like a summer breeze blowing through the trees (or maybe more like a gusty wind that knocks over your lawn furniture).

So what exactly is bytecode? When you write Python code, it gets translated into something called bytecode. This bytecode is then executed by the Python interpreter or compiler. It’s kind of like how a translator takes one language and converts it to another so that people who speak different languages can understand each other (except in this case, we’re talking about computers).

Now, you might be wondering why anyone would care about bytecode instructions. Well, for starters, understanding bytecode is a useful way to answer questions about Python. For example, I often see newer Python programmers wondering why certain constructs are faster than others (like why {} is faster than dict()). Knowing how to access and read Python bytecode lets you work out the answers (try it: dis.dis(“{}”) versus dis.dis(“dict()”)).

But that’s not all! Understanding bytecode also gives a useful perspective on a particular kind of programming that Python programmers don’t often engage in: stack-oriented programming. If you’re unfamiliar with this concept, it basically means working with data structures (like stacks) instead of variables and assignments. It can be a bit mind-bending at first, but once you get the hang of it, it can actually make your code more efficient and easier to understand.

So how do we access Python bytecode instructions? Well, there’s this handy little tool called dis (short for “disassembler”) that comes with Python. It lets us see what our code gets translated into when it’s executed by the interpreter or compiler. To use it, simply run your script through dis and watch the magic happen!

Here’s an example: let’s say we have this simple function in a file called “example.py”:

# This script defines a function called "add_numbers" that takes in two parameters, x and y, and returns the sum of the two numbers.

def add_numbers(x, y): # Defines the function "add_numbers" with two parameters, x and y.
    return x + y # Returns the sum of x and y.

# To use this function, we can call it with two numbers as arguments, like this:
print(add_numbers(5, 10)) # Prints the result of calling the "add_numbers" function with the arguments 5 and 10, which should be 15.

# However, before running our code, let's use the "dis" module to see how our code gets translated into bytecode by the interpreter or compiler.
import dis # Imports the "dis" module, which allows us to disassemble Python bytecode.

# Now, let's use the "dis" module to disassemble our "add_numbers" function.
dis.dis(add_numbers) # Calls the "dis" function on our "add_numbers" function, which will show us the bytecode instructions for our function.

# The output of the "dis" function shows us the bytecode instructions for our "add_numbers" function, which includes loading the two parameters onto the stack, adding them together, and returning the result. This is how our code gets translated into machine-readable instructions for the interpreter or compiler to execute.

To see what bytecode instructions are generated when this function is executed by the interpreter or compiler, run:

# This line executes the python interpreter and uses the dis module to disassemble the bytecode instructions of the example.py file.
python -m dis example.py

This will output a bunch of stuff that looks like this:

# This script is used to add numbers using a function called "add_numbers"

def add_numbers(x, y): # Defining the function "add_numbers" with two parameters, x and y
    return x + y # Returning the sum of x and y

_add_numbers = add_numbers(1, 2) # Calling the function and storing the result in a variable called "_add_numbers"

print(_add_numbers) # Printing the result, which should be 3

# The following code is used to load and store the function "add_numbers" and its result

# Line 2: Loads the function "add_numbers"
# Line 3: Loads the constant value of 1
# Line 6: Stores the function "add_numbers" in a variable called "_add_numbers"
# Line 48: Pops the top value from the stack
# Line 132: Returns the value of the function "add_numbers"

Don’t worry if you don’t understand all of this it can be a bit overwhelming at first. But the important thing is that we now have access to Python bytecode instructions, which gives us a new way to think about and optimize our code!

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