Cell Output Line Length in Editor View #10608

For the NumPy arrays in your screenshot, the setting is NumPy's linewidth. Put this in one marimo cell:

import numpy as np

np.set_printoptions(linewidth=128)
print(np.arange(100))
np.arange(40)

NumPy's default is 75 characters. It inserts breaks between elements, and print(array) and the displayed array(...) representation have different punctuation and indentation. That explains the 72/74-character lines in your example. With the code above, both examples have a 126-character first line. NumPy print options.

For a single print without changing subsequent NumPy output, you can instead use:

print(np.array2string(np.arange(100), max_line_width=128))

The marimo formatting.line_length option controls Python source formatting. It does not set NumPy's output width. This is also how it is described in marimo's configuration schema.

For the separate metadata question: “top of your notebook” means the top of the saved .py file, before import marimo, rather than a code cell in the notebook editor. Open that file in a text editor and place the block at column zero:

# /// script
# [tool.marimo.formatting]
# line_length = 128
# ///
import marimo

# Keep the rest of your existing notebook here.

Keep the # prefixes: marimo reads those comments as TOML metadata; they are not Python statements to execute. Restart the marimo server after editing this metadata. If the file already has a # /// script block, add the settings to that existing block. Script metadata configuration.

I checked the array examples and metadata loading with marimo 0.24.2 on Python 3.10/NumPy 2.2.6 and Python 3.12/NumPy 2.5.3, including exporting a notebook with both outputs.