Document os.open

[techtonik]

BPO	8399
Nosy	@birkenfeld
Files	8399.os-open-default-behavior.diff

^{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 = 'https://github.com/birkenfeld'
closed_at = <Date 2010-04-14.19:17:45.411>
created_at = <Date 2010-04-14.13:26:01.301>
labels = ['type-bug', 'library', 'docs']
title = 'Document os.open'
updated_at = <Date 2010-04-14.19:17:45.410>
user = 'https://bugs.python.org/techtonik'

bugs.python.org fields:

activity = <Date 2010-04-14.19:17:45.410>
actor = 'georg.brandl'
assignee = 'georg.brandl'
closed = True
closed_date = <Date 2010-04-14.19:17:45.411>
closer = 'georg.brandl'
components = ['Documentation', 'Library (Lib)']
creation = <Date 2010-04-14.13:26:01.301>
creator = 'techtonik'
dependencies = []
files = ['16924']
hgrepos = []
issue_num = 8399
keywords = ['patch']
message_count = 5.0
messages = ['103128', '103130', '103131', '103139', '103142']
nosy_count = 2.0
nosy_names = ['georg.brandl', 'techtonik']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue8399'
versions = ['Python 2.6', 'Python 3.1', 'Python 2.7', 'Python 3.2', 'Python 3.3']

[techtonik]

Need to document the that os.O_BINARY flag is obligatory for cross-platform behavior of os.open() on Windows. By default os.open() opens file as binary on Unix, but as text on Windows.

See also bpo-2028 for discussion of making os.O_BINARY default on py3k. I can reopen this issue.

[techtonik]

s/ can / can't /

[birkenfeld]

Since there is no distinction between text and binary mode on Unix, you shouldn't claim the behavior is not consistent - you get text mode. You need O_BINARY on Windows to get binary mode. O_BINARY is already documented; I've added a better link to it from the description of os.open() in r80069.

Do not reopen bpo-2028, it was not about os.open() anyway. For os.open(),
as it is only a wrapper for the OS's own POSIX layer, the flags argument
shouldn't be touched.

[techtonik]

On Unix all files are opened in binary mode. On Windows linefeeds are translated to CRLF corrupting files that are meant to be binary. This is the reason of HgGit failure - it uses Dulwich library that creates corrupted Git index file, because on Windows it is opened without os.O_BINARY flag. Developers do not know anything about it, because they develop on Unix. This could be prevented if we supply a note about how to preserve crossplatform behavior.
https://bugs.edge.launchpad.net/dulwich/+bug/557585

I've attached a patch that adds required note. Please revise it. It should clearly apply over your changes in r80069. I reworded description towards Python users without C background, but I am still worried that they need a POSIX background to understand umask part.

[birkenfeld]

I've added a paragraph about O_BINARY in r80080.