ndarray-npy 0.6.0

.npy and .npz file format support for ndarray


Build status Coverage Dependencies status Crate Documentation Chat

This crate provides support for reading/writing ndarray's ArrayBase type from/to .npy and .npz files. See the documentation for more information.

This crate is a work-in-progress. It currently supports only a subset of .npy header descriptors and supports only primitive fixed-size integer, floating point, and bool types as the array element type. You can implement ReadableElement and WritableElement for your own types, but the next breaking release of this library will probably change those traits.

Future plans include support for:

  • Memory-mapped files.
  • More element types (e.g. structs). If you need support for structs before this is implemented in ndarray-npy, check out the npy crate.
  • Possibly merging this with the npy crate.

Using with Cargo

To use with the default features:

ndarray-npy = "0.6"

The default feature set includes the compressed_npz feature, which enables support for uncompresssed and compressed .npz files. This requires a dependency on the zip crate and a compression backend crate.

To use without the default features:

ndarray-npy = { version = "0.6", default-features = false }

With default-features = false, ndarray-npy provides support only for .npy files, not .npz files. If you want .npz file support, you can select additional features:

  • npz enables support for uncompressed .npz files. This requires a dependency on the zip crate.
  • compressed_npz enables support for uncompressed and compressed .npz files. This requires a dependency on the zip crate and a compression backend crate.

For example, you can use just the npz feature:

version = "0.6"
default-features = false
features = ["npz"]

Library authors

Library authors should specify their dependency on ndarray-npy like this:

version = "0.6"
default-features = false

where the features list is one of the following:

  • [] if your crate does not depend on .npz file support
  • ["npz"] if your crate depends on .npz file support but not compression
  • ["compressed_npz"] if your crate depends on .npz file support with compression


  • 0.6.0

    • Changed write_npy to take the array by reference instead of by value, by @flaghacker.
  • 0.5.0

    • Updated to ndarray 0.13.
    • Updated to Rust 1.38.
    • Added read_npy and write_npy convenience functions.
    • Added support for npy format version 3.0.
    • Renamed ReadableElement::read_vec to ::read_to_end_exact_vec.
    • Refactored the error types and variants, including removing the associated Error type from Readable/WritableElement and updating to the new style of std::error::Error implementation.
    • Updated the padding calculation to make the total header length be divisible by 64 instead of just 16 when writing files. (See numpy/numpy#9025.)
    • Fixed determination of file format version when the addition of padding changes the required version when writing the file.
    • Fixed miscellaneous bugs related to overflow and error handling.
  • 0.4.0

    • Added support for reading/writing arrays of bool, by @tobni and @jturner314.
    • Updated to zip 0.5.
    • Updated to Rust 1.32.
    • Renamed the compressed_npz_default feature to compressed_npz because the zip crate no longer allows the user to select the compression backend.
  • 0.3.0

    • Updated to ndarray 0.12.
    • Updated to num-traits 0.2 (replacing dependency on num).
    • Updated to py_literal 0.2.
  • 0.2.0

    • Updated to zip 0.4.
    • Made the compression backend for compressed .npz files user-selectable.
    • Reworked how feature selection works. This should only affect you if you use default-features = false, features = ["compressed_npz"].
  • 0.1.1

    • Improved crate documentation (no functional changes).
  • 0.1.0

    • Initial release.


Please feel free to create issues and submit PRs. PRs adding more tests would be especially appreciated.


Copyright 2018–2020 Jim Turner and ndarray-npy developers

Licensed under the Apache License, Version 2.0, or the MIT license, at your option. You may not use this project except in compliance with those terms.