---
title: "AST Black Magic: Run synchronous Python code on asynchronous Pyodide - Yuichiro Tachibana"
tags: PyConTW2025, 2025-organize, 2025-共筆
---

# AST Black Magic: Run synchronous Python code on asynchronous Pyodide - Yuichiro Tachibana

{%hackmd L_RLmFdeSD--CldirtUhCw %}

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## Anout the presenter
- Software Artisan / Indie Dev / OSS Enthusiast
- ML Developer Advocate at Hugging Face
- Stramlit Creator
- [whitphx.info](https://www.whitphx.info/)

## AST
- AST (Abstract Syntax Tree) in Python is a tree representation of the parsed source code structure.
- The behavior of a source code can be modified with AST without modifying the source code itself

### Applications of AST
- Linter
- Code Analysis
- Code Refactoring

## Pyodide
- Python in javascript

### Issues
- Executes Python code in WebAssembly, which has a different nature than our usual environment
- Single-threaded
- Browser's event loop
- some Python features do not work as expected
- This talk focus on asynchronous method

|Not working in pyodide| Should use|
|:--|:--|
|`asyncio.run(fn())`|`await fn()`|
|`time.sleep(1)`|`await asyncio.sleep(1)`|

### Motivation
- We don't want to rewrite the code
- Should be able to run inside pyodide if it can be used in usual python
- Using AST for this

#### Simple Solution

# parse time.sleep and 
# transform to await asyncio.sleep

**Issue**: What if the function to be modified locates inside another function? --> Custom Name Resolution

#### Name Resolution

**Issue**:
- Chain reaction
- File overwrite key functions
- Dynamic behavior
- --> Determine the line we're going to support

#### Give up

## Summary
- AST-based approach
- can achieve syntax-level code modification
- has limitations

Below is the part that speaker updated the talk/tutorial after speech
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