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DOC: Clarify float-to-int truncation behavior in numpy.array_split documentation #29511

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DOC: Clarify float-to-int truncation behavior in numpy.array_split documentation #29511

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@JRedrupp JRedrupp commented Aug 5, 2025

Summary

Fixes #29494 by clarifying how numpy.array_split handles floating-point inputs.

Changes

  • Added comprehensive Parameters section: Documents that floating-point indices_or_sections values are truncated towards zero using int() before splitting
  • Added practical example: Shows np.array_split(x, 3.9) being treated as np.array_split(x, 3)
  • Added Returns section: For documentation completeness
  • Fixed doctest formatting: Corrected spacing in existing array output examples for consistency

Example of the clarified behavior

import numpy as np
x = np.arange(10)

# These are equivalent:
np.array_split(x, 3.9)  # Treated as 3
np.array_split(x, 3)
# Both return: [array([0, 1, 2, 3]), array([4, 5, 6]), array([7, 8, 9])]

@JRedrupp
DOC: clarify float truncation behavior in array_split
d5627e8 
Add comprehensive documentation explaining that floating-point
indices_or_sections values are truncated towards zero using int()
before splitting. This addresses user confusion about unexpected
behavior when passing float values like 3.9 to array_split.

Changes:
- Add Parameters section documenting float truncation behavior
- Add example showing np.array_split(x, 3.9) treated as 3 sections
- Add Returns section for completeness
- Fix existing doctest formatting for consistency

Closes numpygh-29494
seberg
seberg reviewed Aug 8, 2025
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numpy/lib/_shape_base_impl.py

If `indices_or_sections` is a floating-point number, it will be
truncated towards zero (equivalent to ``int()``) before splitting.
For example, ``3.9`` is treated as ``3``.
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I don't care if this is true, but let's not document the float input. If anything, that should be deprecated.

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DOC: Clarify float-to-int truncation behavior in numpy.array_split documentation
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