[Python-Dev] Dropping __init__.py requirement for subpackages

"Martin v. Löwis" martin at v.loewis.de
Wed Apr 26 22:17:58 CEST 2006

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).


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