view mercurial/txnutil.py @ 43104:74802979dd9d

py3: define and use pycompat.itervalues()

.itervalues() only exists on Python 2. Python 3's equivalent is
.values(). But we don't want to blindly use .values() everywhere
because on Python 2, it will create a list, which will have performance
implications.

This commit introduces pycompat.itervalues() which will call the appropriate
method on the passed object. We update all callers of obj.itervalues()
to pycompat.itervalues(obj) instead.

With this commit, the only source tranforming remaining is for
iteritems(). Victory is near...

Differential Revision: https://phab.mercurial-scm.org/D7013

# txnutil.py - transaction related utilities
#
#  Copyright FUJIWARA Katsunori <[e-mail]> and others
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

from __future__ import absolute_import

import errno

from . import encoding


def mayhavepending(root):
    '''return whether 'root' may have pending changes, which are
    visible to this process.
    '''
    return root == encoding.environ.get(b'HG_PENDING')


def trypending(root, vfs, filename, **kwargs):
    '''Open  file to be read according to HG_PENDING environment variable

    This opens '.pending' of specified 'filename' only when HG_PENDING
    is equal to 'root'.

    This returns '(fp, is_pending_opened)' tuple.
    '''
    if mayhavepending(root):
        try:
            return (vfs(b'%s.pending' % filename, **kwargs), True)
        except IOError as inst:
            if inst.errno != errno.ENOENT:
                raise
    return (vfs(filename, **kwargs), False)