Getting around multiple definition errors

marimo does not allow the same variable to be defined in multiple cells. This restriction guarantees that the code on the page matches the outputs you see, eliminates hidden state and hidden bugs, and lets marimo run your notebooks as web apps and scripts, but it also has a learning curve. Here are some tips to help you adapt.

Learn more

Check out our guide on multiple definition errors to learn more, or watch our YouTube video.

Source code for examples/running_cells/multiple_definitions.py

Tip: paste this code into an empty cell, and the marimo editor will create cells for you

# /// script
# requires-python = ">=3.12"
# dependencies = [
#     "marimo",
#     "matplotlib==3.10.1",
# ]
# ///
import marimo

__generated_with = "0.12.9"
app = marimo.App()


@app.cell
def _():
    import marimo as mo
    return (mo,)


@app.cell(hide_code=True)
def _(mo):
    mo.md(
        r"""
        ## Use local variables

        Variables prefixed with an underscore are local to a cell, and can be redefined.
        """
    )
    return


@app.cell
def _():
    for _i in range(3):
        print(_i)
    return


@app.cell
def _():
    for _i in range(4, 6):
        print(_i)
    return


@app.cell
def _():
    # _i is not defined in this cell
    _i
    return


@app.cell(hide_code=True)
def _(mo):
    mo.md(
        r"""
        ## Wrap code in functions

        Wrap cells in functions to minimize the number of temporary globals you introduce.
        """
    )
    return


@app.cell
def _():
    import matplotlib.pyplot as plt
    return (plt,)


@app.cell
def _(plt):
    def _():
        fig, ax = plt.subplots()
        plt.plot([1, 2])
        return ax

    _()
    return


if __name__ == "__main__":
    app.run()