Скачать или смотреть How to Handle None or Numpy Arrays as Default Arguments in Pybind11

Learn how to bind C+ + functions to Python using Pybind11, enabling default arguments to be `None` or Numpy arrays while ensuring compatibility with your native C+ + code.
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Handling None or Numpy Arrays as Default Arguments in Pybind11

When working with Python and C+ + using Pybind11, one common challenge is passing arguments that can accept either a None value or a Numpy array. Many developers face this issue when they need to bind their C+ + functions to Python while maintaining flexibility in the function parameters. In this guide, we’re going to explore a practical solution to this problem, allowing your C+ + functions to work seamlessly with Numpy arrays and None simultaneously.

The Problem

You want to create a C+ + function that can accept a Numpy array or None as a default argument. An example case could be a function named fit where the third parameter, dubbed mask, can either be None (indicating no mask is used) or a Numpy array (mask values the same size as another input variable). Here's a snippet of what you're aiming for:

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The Solution

To handle this effectively in your C+ + code when using Pybind11, you can utilize std::optional from C+ + 17, which provides an elegant way to represent optional parameters. If you are using an earlier version of C+ + , consider using a backported optional.h. Here’s how to implement this in your function:

Step 1: Define the C+ + Function

You begin by changing your function signature to use std::optional. Here’s a modified signature for your fit function:

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Step 2: Binding in Pybind11

Next, configure the Pybind11 module to recognize this optional parameter. The following code sets up the binding, marking the mask argument with a default value of py::none(), which corresponds to None in Python:

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Step 3: Example Python Calls

This setup allows your Python users to easily call the fit function as illustrated below:

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Conclusion

By utilizing std::optional in conjunction with Pybind11, you can effectively manage default arguments that can be either None or Numpy arrays. This approach not only streamlines the binding process but also enhances the flexibility and functionality of your C+ + functions when accessed through Python.

This simple yet powerful tactic allows developers to construct robust applications that interface seamlessly between Python and C+ + . Feel free to incorporate this pattern in your Pybind11 projects to enhance your code’s usability and maintainability!