When modifying code in cell with preexecution hook, old code is executed

[ajwheeler]

As I understand it, the only way to programmatically modify code is with IJulia.load_string. It seems that if a function using this is registered as a preexecution hook, it modifies the cell as expected, but only after running the unmodified code. JupyterFormatter is where I first noticed this behavior, and it's source is a nearly minimal example of the workflow I'm describing.

It would be really nice to be able to modify the code, and then execute it immediately, without running the cell twice. Is this possible, or it is a limitation of the way Jupyter works?

[stevengj]

It's the way Jupyter works — it sends us the code to be executed, at which point we execute the hooks, but at that point it has already sent us the old code.