[Python-Dev] Dropping init.py requirement for subpackages (original) (raw)
"Martin v. Löwis" martin at v.loewis.de
Wed Apr 26 22:17:58 CEST 2006
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Phillip J. Eby wrote:
At 11:50 AM 4/26/2006 -0700, Guido van Rossum wrote:
I'm not sure what you mean by "one directory read". You'd have to list the entire directory, which may require reading more than one block if the directory is large. You have to do this to find an init.py too, don't you? Technically, there's going to be a search for a .pyc or .pyo first, anyway.
No. Python does stat(2) and open(2) to determine whether a file is present in a directory. Whether or not that causes a full directory scan depends on the operating system. On most operating systems, it is not a full directory scan:
- on network file systems, the directory is read only on the server; a full directory read would also cause a network transmission of the entire directory contents
- on an advanced filesystem (such as NTFS), a lookup operation is a search in a balanced tree, rather than a linear search, bypassing many directory blocks for a large directory
- on an advanced operating system (such as Linux), a repeated directory lookup for the file will not go to the file system each time, but cache the result of the lookup in an efficient memory structure. In all cases, the directory contents (whether read from disk into memory or not) does not have to be copied into python's address space for stat(2), but does for readdir(3).
Regards, Martin
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