🔒 What is a pyc file for?

[prime rock]

I know that it’s a cached precompiled binary version of your Python file, but what is it for?

[obsidian ferry]

@prime rock

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[gray plaza]

it can improve runtime of subsequent runs

[fluid widget]

that's all it is. you can just ignore that it's there.
if you try to run a py file, and it hasn't changed since the last time a pyc file was created for it, python will secretly use the pyc file.

[prime rock]

Oh, thanks.

[hardy prairie]

What’s in it then?

And if there’s a syntax error, does the pyc get made?

[fair wyvern]

They contain Python bytecode which is basically instructions that are generated from your code and that are then run by Python.

[fair wyvern]

And no, syntax errors are detected way before bytecode is generated. But for other runtime errors that don't inmediately happen when the module is imported, I'd imagine that yeah.

[hardy prairie]

Is the byte code something you can execute in some way instead of having the python file? Is that possible somehow in order to make things more efficient? And is the bytecode unique to each processor? X

[fair wyvern]

I believe you can just run it as you would any Python file (assuming the .pyc file was made for that version). And theoretically, yes, it could make things a bit faster since you're skipping the compilation step. So that's what Python does if it sees a .pyc file, it runs that instead of having to recompile the Python file (as long as it hasn't changed). Bytecode is machine-independent so no. It will depend on the version of Python.

[fluid widget]

You shouldn't try to distribute pyc files. They're an implementation detail and there's no guarantee that they'll work anywhere else @hardy prairie @prime rock

[raven moss]

a pyc file contains python bytecode, which is interpreted by your python interpreter. it's cross platform but rarely cross version

you can technically read, manipulate and write back pyc files using marshal and code objects, but there's no official api to modify the instruction bytes

you can dump the instructions with dis

[hardy prairie]

Really interesting

[raven moss]

i made https://github.com/0x3C50/pyasm a while back, it can actually generate python 3.11 code objects you can then write as a pyc with marshal

[hardy prairie]

So. When we say Python is an interpreted language… it’s not really strictly true. It’s complied and then run on a Python “machine” a bit like Java? Is that correct?

[raven moss]

correct

its very similar to java actually, you just dont see the pyc files as a way to distribute apps

[hardy prairie]

When it’s taught in schools in the uk we teach that it’s interpreted. Now I feel bad that I’m lying.

[raven moss]

but its the same source -> bytecode -> interpreting pipeline

[raven moss]

no it is still interpreted in a sense

[hardy prairie]

Would you consider Java to be interpreted then?

[raven moss]

kinda

but java also jit compiles its bytecode to actual machine code

[outer egret]

Interpretation and compilation and not exclusive of each other. "Compilation" just means "translation" essentially.

[hardy prairie]

I always state that you need source code to run an interpreted program and it reads it line by line. But that might not be the case.

[raven moss]

python also recently started doing that btw

[raven moss]

yeah thats false

at least the line by line part

[hardy prairie]

Yet I need to teach this as the exams state this. Boo. 😒

Good to know the truth though

[hardy prairie]

Well, I tend to state that compiled code doesn’t need the source code for it to run.

[hardy prairie]

So Python has sort of changed to a compiled bytecode language from an interpreted language recently.

[outer egret]

That's not false I don't think, but it's not a great distinction.

[outer egret]

I don't think Python was ever strictly interpreted. In fact, I don't know of any non-trivial language that's strictly interpreted. Intermediate bytecode compilation is very common.

[raven moss]

fun fact: python can run pyc files directly. in that sense its similar to java

there's also .pyz files, also directly runnable, which are zip bundles of multiple py or pyc files

... similar to java's jars

python = java confirmed??

[raven moss]

eh

the main feature is still running py files from source

but, java can also do that...

java = interpreted language??

you see its complicated

[hardy prairie]

Yeah. Fascinating.

[obsidian ferry]

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