Inconsistent behavior: Get st_nlink from os.stat() and os.scandir()

[MohansonLeaf]

BPO	28041
Nosy	@pfmoore, @vstinner, @tjguk, @zware, @zooba, @MojoVampire
PRs	bpo-28041: Inconsistent behavior: Get st_nlink from os.stat() and os.scandir() #795
Files	stat.py: python3.5 stat.py

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2017-04-21.23:46:00.386>
created_at = <Date 2016-09-09.09:24:54.047>
labels = ['type-bug', 'invalid', 'OS-windows']
title = 'Inconsistent behavior: Get st_nlink from os.stat() and os.scandir()'
updated_at = <Date 2017-04-21.23:46:00.384>
user = 'https://bugs.python.org/MohansonLeaf'

bugs.python.org fields:

activity = <Date 2017-04-21.23:46:00.384>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2017-04-21.23:46:00.386>
closer = 'vstinner'
components = ['Windows']
creation = <Date 2016-09-09.09:24:54.047>
creator = 'Mohanson Leaf'
dependencies = []
files = ['44494']
hgrepos = []
issue_num = 28041
keywords = []
message_count = 3.0
messages = ['275293', '290072', '292085']
nosy_count = 7.0
nosy_names = ['paul.moore', 'vstinner', 'tim.golden', 'zach.ware', 'steve.dower', 'josh.r', 'Mohanson Leaf']
pr_nums = ['795']
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue28041'
versions = ['Python 3.5']

[MohansonLeaf]

os.stat(file).st_nlink gives 1 but same file's st_nlink from os.scandir(dir) gives 0.

"""
Inconsistent behavior: Get st_nlink from os.stat() and os.scandir()
Platform: Python 3.5.1 (v3.5.1:37a07cee5969, Dec 6 2015, 01:38:48) [MSC v.1900 32 bit (Intel)] on win32
"""

import os
import os.path

print('os.stat:', os.stat(file).st_nlink)

for entry in os.scandir(os.path.dirname(os.path.abspath(__file__))):
    if entry.name == 'stat.py':
        print('os.scandir:', entry.stat().st_nlink)

"""
os.stat: 1
os.scandir: 0
"""

[MojoVampire]

This is documented behavior. Per the docs for os.DirEntry's stat method (the objects yielded by os.scandir):

On Windows, the st_ino, st_dev and st_nlink attributes of the stat_result are always set to zero. Call os.stat() to get these attributes.

It might be nice if those values could be cached on read (through a lazily initialized value on property access or the like), but this is not a bug, it's working as documented.

[vstinner]

scandir () is designed for effiency, not for portability or correctness. The API has deliberate limitations which are well documented, as the one you spotted:
https://docs.python.org/dev/library/os.html#os.DirEntry.stat

Your PR would defeat the whole purpose of scandir.