In JupyterLab, you can run a specific Python instruction (or a set of instructions) before each cell execution using startup scripts or cell magic commands. Here are the most common and effective methods:

---

1. Using %run Magic Command

You can use the %run magic command at the top of your notebook to execute a script before running any cell. However, this only runs once at the start, not before each cell.

---

2. Using %%capture and %automagic (Not Recommended for This Use Case)

These are not directly useful for running code before each cell, but are mentioned for completeness.

---

3. Using IPython Startup Files

You can create a startup script that runs every time a Jupyter kernel starts. This is useful for imports or configurations, but not for running code before each cell.

1. Create a file (e.g., startup.py) in the IPython profile startup directory:

   python
   Copy
   # Find your profile directory:
   !jupyter --paths

   Place your script in the startup folder of your profile directory.

2. Add your code to startup.py. This will run when the kernel starts, not before each cell.

---

4. Using a Custom IPython Extension

You can write a custom IPython extension to run code before each cell execution. This is more advanced but gives you full control.

Example:

1. Create a file my_extension.py:

   python
   Copy
   def load_ipython_extension(ipython):
       def pre_run_cell(info):
           print("Running before each cell!")
           # Add your code here
       ipython.events.register('pre_run_cell', pre_run_cell)

2. Install the extension:

   bash
   Copy
   ipython register my_extension.py

3. Load the extension in your notebook:

   python
   Copy
   %load_ext my_extension

---

5. Using %autorun (Not Native, Requires Custom Setup)

There is no native %autorun magic, but you can simulate this behavior with a custom solution.

---

6. Using a Notebook Initialization Cell

• Create a cell at the top of your notebook with the code you want to run before each cell.
• Use the %%capture magic to suppress output if needed.
• Manually re-run this cell before each new cell, or use a notebook extension to automate this.

---

7. Using Jupyter Notebook Extensions

There are third-party extensions (like jupyter-contrib-nbextensions) that allow you to run a cell automatically before others, but this is not built into JupyterLab by default.

---

Best Practical Solution

If you want to run a specific instruction before each cell, the most practical approach is to:

• Use a function: Define a function with your setup code and call it at the start of each cell.
• Use a notebook template: Start each notebook with a setup cell and run it first.

---

Example:

python
Copy
def setup():
    print("Running setup code!")
    # Your setup code here

setup()  # Call this at the start of each cell

---