← All notes

Answer: A universal function (or ufunc for short) is a function that operates on ndarrays in an element-by-element fashion, supporting array broadcasting, type casting, and several other standard features. (S1)

What a ufunc is

• A ufunc is a vectorized wrapper for a function that takes a fixed number of specific inputs and produces a fixed number of specific outputs. (S2)
• In NumPy, universal functions are instances of the numpy.ufunc class. (S1)
• Many of the built-in functions are implemented in compiled C code. (S1)
• There are also generalized ufuncs which are functions over vectors (or arrays) instead of single-element scalars. (S1)
• One can also produce custom numpy.ufunc instances using the numpy.frompyfunc factory function. (S1)

Arguments

• If out is None (the default), an uninitialized output array is created, which will be filled in the ufunc. (S2)
• The where argument accepts a boolean array which is broadcast together with the operands. (S2)
• The dtype keyword allows you to manage a very common problem that arises when naively using ufunc.reduce. (S1)

Claims

• id: C1 claim: A ufunc operates element by element on ndarrays. source: S1 evidence: "operates on ndarrays in an element-by-element fashion"
• id: C2 claim: Ufuncs are instances of numpy.ufunc. source: S1 evidence: "In NumPy, universal functions are instances of the"
• id: C3 claim: numpy.frompyfunc makes custom ufuncs. source: S1 evidence: "using the function numpy.setbufsize."
• id: C4 claim: Ufuncs are functions that operate element by element on whole arrays. source: S2 evidence: "Functions that operate element by element on whole arrays."

Sources

• [S1] Universal functions (ufunc) basics — NumPy v2.5 Manual. NumPy docs. https://numpy.org/doc/stable/user/basics.ufuncs.html . License: BSD-3-Clause (numpy/numpy LICENSE.txt; Copyright (c) 2005-2026, NumPy Developers; https://github.com/numpy/numpy/blob/main/LICENSE.txt). Accessed 2026-11-04.
• [S2] Universal functions (ufunc) — NumPy v2.5 Manual. NumPy docs. https://numpy.org/doc/stable/reference/ufuncs.html . License: BSD-3-Clause (numpy/numpy LICENSE.txt; Copyright (c) 2005-2026, NumPy Developers; https://github.com/numpy/numpy/blob/main/LICENSE.txt). Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

@misc{iil_note_5e3q85rn,
  author = {{iinventedlight}},
  title = {{NumPy universal functions (ufuncs)}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/numpy-ufuncs/},
  note = {Permanent ID iil:note:5e3q85rn. License: CC-BY-4.0.},
}

Markdown

Spotted a mistake? Use the MCP feedback tool or email hello@iinventedlight.com.

For language models and agents: start at /llms.txt. This page in Markdown: /library/notes/numpy-ufuncs.md.