NumPy SystemError: New style getargs format but argument is not a tuple

Introduction

NumPy is a popular Python library for numerical computing, but sometimes users may encounter the “SystemError: new style getargs format but argument is not a tuple” error. This error often confuses developers as it relates to interactions with NumPy’s underlying C API rather than direct Python code. In this tutorial, we’ll explore the reasons behind this error and offer several solutions to resolve it.

Reason for the Error

The mentioned error usually occurs when using NumPy’s array interface with functions expecting a tuple of arguments but instead receive a different data type. Here is why it occurs:

• Type Mismatch: The most common reason is that a function that requires a tuple receives an argument of a different type.
• Incompatible Data Structures: This error also happens when incompatible or unsupported data structures are passed as arguments to NumPy functions that use the new-style ‘getargs’ format.
• Incorrect Extension Behavior: This error can surface from incorrectly implemented custom NumPy data types or extension codes that interface poorly with NumPy’s C API.

Solutions to Fix the Error

Solution 1: Pass Arguments as a Tuple

The simplest and most direct solution is to ensure you are passing a tuple of arguments to functions that expect it. This typical mistake is easy to solve.

1. Check the function documentation to verify the expected argument format.
2. Adjust your function calls to pass the arguments as a tuple.

Example:

import numpy as np

# Correct way to pass arguments as a tuple
def do_something(*args):
    return np.array(args)

data = do_something(1, 2, 3)
print(data)

Output:

[1 2 3]

Notes: This solution is simple and works in most cases where you have control over the calling code. Check your calls to NumPy functions and ensure that arguments expected as tuples are indeed tuples.

Solution 2: Update or Fix Custom Extensions

If you are working on a custom NumPy extension or using a third-party extension, ensure it is compatible with NumPy’s ‘getargs’ format.

1. Review any custom extensions to ensure they are implemented correctly according to NumPy’s C API requirements.
2. Update the extension or contact the author if you are using third-party extensions.

Notes: This is a more complex solution that requires knowledge of C and the NumPy API. It is mainly applicable when you are developing C extensions that interact with NumPy.

Solution 3: Use NumPy’s Built-in Functions

Instead of custom operations, try to use NumPy built-in functions since they are optimized and unlikely to cause this error.

1. Identify the operation causing the error.
2. Find a built-in NumPy function that accomplishes the same task.
3. Replace your custom operation with the NumPy built-in function.

Notes: This is the best practice for performance and reliability. Make sure you understand the built-in functions available in NumPy before developing your custom operations.

Conclusion

This tutorial presented common reasons and solutions for the “SystemError: new style getargs format but argument is not a tuple” in NumPy. Accurate handling of data types and use of official APIs and documentation can prevent such errors. When encountered, verifying argument types and relying on tested NumPy functions can help troubleshoot and solve the issue.