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# NumPy compatibility

NumPy forms an essential basis for astropy, and astropy’s development has led to the identification of problems with some of numpy’s functionality. Often, these are corrected in later versions of numpy, but in order for astropy not to depend on these, work-arounds are made, usually in the code. If functions are used in more than one place, however, it can be more convenient to provide patched routines. Hence, `astropy.utils.compat.numpy`.

## Adding a patched routine

To ensure that patched code is only used when required, and that it will be easy to remove it if it is no longer needed for any supported version of NumPy, the following procedure should be used to add a patched routine:

- Copy over a correct version of the relevant numpy file to its corresponding location below the `astropy/utils/compat/numpy` directory.
- In this file, remove everything that does not have to be changed. If necessary, import required pieces from numpy.
- Define a function that tests whether or not a patched version is needed, by directly testing whether the desired functionality is present. Suggested function names are `PR####` with a relevant numpy pull request number, or `GE####` with a version number.
- Place the redefinition of the relevant piece of code inside an `if` statement that uses the function just defined. This should ensure that if a sufficiently high version of numpy is used, no replacement is made.
- In `numpy/__init__.py`, import your patched code.
- In `numpy/tests`, add a new test routine that tests that the patch is used when necessary (i.e., test the test function), and that it provides the desired functionality.

For an example, see `numpy/lib/stride_tricks.py` and the corresponding `numpy/tests/test_broadcast_arrays.py`.

Note that patched routines will normally only be considered if they are part of NumPy. Thus, if the patch concerns a new bug discovered in numpy, a pull request should first be made to NumPy (which can of course form the basis of a pull request to `astropy`).

# Reference/API

## astropy.utils.compat.numpy Package

NumPy functions and classes needed for astropy but not available in all supported NumPy versions. See docs/utils/numpy.rst for details.