pathlib: Path.iterdir() is surprisingly not streaming

Bug report

Suprisingly (contrary to its name and being a generator), Path.iterdir() does not stream directory entries:

It reads all directory entries into memory before yielding the first entry.

This can cause excessive memory usage when "iterating" over very large directories.

Users would expect by default that .iterdir() operates in a streaming way, like UNIX find or readdir(), streaming e.g. the results of the underlying system calls such as getdents64() on Linux.

But it does entries = list(scandir_it) instead:

https://github.com/python/cpython/blob/c419af9e277bea7dd78f4defefc752fe93b0b8ec/Lib/pathlib/__init__.py#L835-L843

This should be documented, and can hopefully be fixed without too much breakage.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Related issues

• https://github.com/python/cpython/issues/129871

Linked PRs

• gh-136060

Inizia da Lib/pathlib/init.py, nell’implementazione collegata di Path.iterdir() intorno alle righe 835-843, quindi esamina l’issue correlata 129871 e la PR collegata 136060. Conferma il comportamento di iterazione previsto e le aspettative di compatibilità; il lavoro è completo quando il comportamento di streaming dell’issue è stato gestito ed è coperto dai test pathlib pertinenti.