Top-Level Imports vs. Lazy Imports: Which is More Efficient in Python?

Module Importing Location: at the Top or When Needed?

PEP 8 states the convention of placing imports at the top of a module. However, there is a debate around whether it is more efficient to import when needed.

Argument for Lazy Importing

The argument for lazy importing suggests that unnecessary imports can impact efficiency, especially when a class, method, or function is only rarely used. This could justify moving the import within the function to optimize performance.

Efficiency Considerations

However, module importing is relatively fast. Placing imports at the top of the module is a minimal cost paid once. In contrast, moving imports within functions increases the execution time for those functions.

Best Practices

If efficiency is a concern, placing imports at the top of the module is advisable. Only consider lazy imports if profiling reveals that it would significantly improve performance.

Additional Justifications for Lazy Imports

While efficiency may not be a compelling reason for lazy imports, there are other valid scenarios:

• Optional library support: Code with multiple paths can avoid breaking if an optional library is not installed.
• Plugin initialization: In plugin __init__.py files, lazy imports are beneficial as plugins may be imported but not always used.

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