dd4fc36a9d
When the second argument of an assert statement is a string, using repr() is more helpful than relying on the default representation.
379 lines
12 KiB
Python
379 lines
12 KiB
Python
# -*- coding: utf-8 -*-
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# virtual_path.py --- Classes used to manipulate slash-separated virtual paths
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#
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# Copyright (C) 2018 Florent Rougon
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#
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# This program is free software; you can redistribute it and/or
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# modify it under the terms of the GNU General Public License as
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# published by the Free Software Foundation; either version 2 of the
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# License, or (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful, but
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# WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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# General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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"""Module containing the VirtualPath and MutableVirtualPath classes."""
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import pathlib
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class VirtualPath:
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"""Class used to represent paths inside the TerraSync repository.
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This class always uses '/' as the separator. The root path '/'
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corresponds to the repository root, regardless of where it is stored
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(hard drive, remote server, etc.).
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Note: because of this, the class is not supposed to be used directly
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for filesystem accesses, since some root directory or
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protocol://server/root-dir prefix would have to be prepended
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to provide reasonably useful functionality). This is why the
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class is said to be virtual. This also implies that even in
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Python 3.6 or later, the class should *not* inherit from
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os.PathLike.
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Wherever a given feature exists in pathlib.PurePath, this class
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replicates the corresponding pathlib.PurePath API.
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"""
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def __init__(self, p):
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# Once this function exits, self._path *must not be changed* anymore
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# (doing so would violate the contract for a hashable object: the
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# hash must not change once the object has been constructed).
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self._path = self.normalizeStringPath(p)
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# This check could of course be skipped if it is found to really affect
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# performance.
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self._check()
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def __str__(self):
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return self._path
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def __repr__(self):
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return "{}.{}({!r})".format(__name__, type(self).__name__, self._path)
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def __lt__(self, other):
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# Allow sorting with instances of VirtualPath, or of any subclass. Note
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# that the == operator (__eq__()) and therefore also != are stricter
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# with respect to typing.
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if isinstance(other, VirtualPath):
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return self._path < other._path
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else:
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return NotImplemented
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def __le__(self, other):
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if isinstance(other, VirtualPath):
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return self._path <= other._path
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else:
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return NotImplemented
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def __eq__(self, other):
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# The types must be the same, therefore a VirtualPath never compares
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# equal to a MutableVirtualPath with the == operator. For such
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# comparisons, use the samePath() method. If __eq__() (and thus
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# necessarily __hash__()) were more lax about typing, adding
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# VirtualPath instances and instances of hashable subclasses of
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# VirtualPath with the same _path to a set or frozenset would lead to
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# unintuitive behavior, since they would all be considered equal.
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return type(self) == type(other) and self._path == other._path
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def __gt__(self, other):
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if isinstance(other, VirtualPath):
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return self._path > other._path
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else:
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return NotImplemented
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def __ge__(self, other):
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if isinstance(other, VirtualPath):
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return self._path >= other._path
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else:
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return NotImplemented
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def __hash__(self):
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# Be strict about typing, as for __eq__().
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return hash((type(self), self._path))
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def samePath(self, other):
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"""Compare the path with another instance, possibly of a subclass.
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other -- instance of VirtualPath, or of a subclass of
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VirtualPath
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"""
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if isinstance(other, VirtualPath):
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return self._path == other._path
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else:
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raise TypeError("{obj!r} is of type {klass}, which is neither "
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"VirtualPath nor a subclass thereof"
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.format(obj=other, klass=type(other).__name__))
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def _check(self):
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"""Run consistency checks on self."""
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assert (self._path.startswith('/') and not self._path.startswith('//')
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and (self._path == '/' or not self._path.endswith('/'))), \
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repr(self._path)
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@classmethod
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def normalizeStringPath(cls, path):
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"""Normalize a string representing a virtual path.
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path -- input path (string)
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Return a string that always starts with a slash, never contains
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consecutive slashes and only ends with a slash if it's the root
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virtual path ('/').
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If 'path' doesn't start with a slash ('/'), it is considered
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relative to the root. This implies that if 'path' is the empty
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string, the return value is '/'.
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"""
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if not path.startswith('/'):
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# / is the “virtual root” of the TerraSync repository
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path = '/' + path
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elif path.startswith('//') and not path.startswith('///'):
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# Nasty special case. As allowed (but not mandated!) by POSIX[1],
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# in pathlib.PurePosixPath('//some/path'), no collapsing happens[2].
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# This is only the case for exactly *two* *leading* slashes.
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# [1] http://pubs.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap04.html#tag_04_11
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# [2] https://www.python.org/dev/peps/pep-0428/#construction
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path = path[1:]
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return pathlib.PurePosixPath(path).as_posix()
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def __truediv__(self, s):
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"""Path concatenation with the '/' operator.
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's' must be a string representing a relative path using the '/'
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separator, for instance "dir/subdir/other-subdir".
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Return a new instance of type(self).
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"""
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assert not (s.startswith('/') or s.endswith('/')), repr(s)
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if self._path == '/':
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return type(self)(self._path + s)
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else:
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return type(self)(self._path + '/' + s)
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def joinpath(self, *args):
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"""Combine 'self' with each given string argument in turn.
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Each argument should be of the form "foo", "foo/bar",
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"foo/bar/baz", etc. Return the corresponding instance of
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type(self).
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>>> p = VirtualPath("/foo").joinpath("bar", "baz", "quux/zoot")
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>>> str(p)
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'/foo/bar/baz/quux/zoot'
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"""
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return self / '/'.join(args)
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@property
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def name(self):
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"""Return a string representing the final path component.
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>>> p = VirtualPath("/foo/bar/baz")
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>>> p.name
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'baz'
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"""
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pos = self._path.rfind('/')
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assert pos != -1, (pos, self._path)
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return self._path[pos+1:]
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@property
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def parts(self):
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"""Return a tuple containing the path’s components.
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>>> p = VirtualPath('/usr/bin/python3')
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>>> p.parts
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('/', 'usr', 'bin', 'python3')
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"""
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if self._path == "/":
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return ('/',)
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else:
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# Skip the leading slash before splitting
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return ('/',) + tuple(self._path[1:].split('/'))
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def generateParents(self):
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"""Generator function for the parents of the path.
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See the 'parents' property for details.
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"""
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if self._path == '/':
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return
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assert self._path.startswith('/'), repr(self._path)
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prevPos = len(self._path)
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while True:
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pos = self._path.rfind('/', 0, prevPos)
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if pos > 0:
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yield type(self)(self._path[:pos])
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prevPos = pos
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else:
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assert pos == 0, pos
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break
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yield type(self)('/')
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@property
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def parents(self):
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"""The path ancestors.
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Return an immutable sequence providing access to the logical
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ancestors of the path.
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>>> p = VirtualPath('/foo/bar/baz')
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>>> len(p.parents)
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3
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>>> p.parents[0]
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terrasync.virtual_path.VirtualPath('/foo/bar')
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>>> p.parents[1]
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terrasync.virtual_path.VirtualPath('/foo')
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>>> p.parents[2]
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terrasync.virtual_path.VirtualPath('/')
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"""
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return tuple(self.generateParents())
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@property
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def parent(self):
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"""The logical parent of the path.
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>>> p = VirtualPath('/foo/bar/baz')
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>>> p.parent
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terrasync.virtual_path.VirtualPath('/foo/bar')
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>>> q = VirtualPath('/')
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>>> q.parent
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terrasync.virtual_path.VirtualPath('/')
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"""
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pos = self._path.rfind('/')
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assert pos >= 0, pos
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if pos == 0:
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return type(self)('/')
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else:
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return type(self)(self._path[:pos])
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@property
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def suffix(self):
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"""The extension of the final component, if any.
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>>> VirtualPath('/my/library/setup.py').suffix
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'.py'
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>>> VirtualPath('/my/library.tar.gz').suffix
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'.gz'
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>>> VirtualPath('/my/library').suffix
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''
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"""
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name = self.name
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pos = name.rfind('.')
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return name[pos:] if pos != -1 else ''
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@property
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def suffixes(self):
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"""A list of the path’s extensions.
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>>> VirtualPath('/my/library/setup.py').suffixes
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['.py']
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>>> VirtualPath('/my/library.tar.gz').suffixes
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['.tar', '.gz']
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>>> VirtualPath('/my/library').suffixes
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[]
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"""
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name = self.name
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prevPos = len(name)
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l = []
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while True:
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pos = name.rfind('.', 0, prevPos)
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if pos == -1:
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break
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else:
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l.insert(0, name[pos:prevPos])
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prevPos = pos
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return l
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def asRelative(self):
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"""Return the virtual path without its leading '/'.
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>>> p = VirtualPath('/usr/bin/python3')
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>>> p.asRelative()
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'usr/bin/python3'
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>>> VirtualPath('').asRelative()
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''
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>>> VirtualPath('/').asRelative()
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''
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"""
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assert self._path.startswith('/'), repr(self._path)
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return self._path[1:]
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class MutableVirtualPath(VirtualPath):
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"""Mutable subclass of VirtualPath.
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Contrary to VirtualPath objects, instances of this class can be
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modified in-place with the /= operator, in order to append path
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components. The price to pay for this advantage is that they can't
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be used as dictionary keys or as elements of a set or frozenset,
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because they are not hashable.
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"""
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__hash__ = None # ensure the type is not hashable
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def _normalize(self):
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self._path = self.normalizeStringPath(self._path)
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def __itruediv__(self, s):
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"""Path concatenation with the '/=' operator.
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's' must be a string representing a relative path using the '/'
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separator, for instance "dir/subdir/other-subdir".
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"""
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# This check could of course be skipped if it is found to really affect
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# performance.
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self._check()
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assert not (s.startswith('/') or s.endswith('/')), repr(s)
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if self._path == '/':
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self._path += s
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else:
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self._path += '/' + s
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# Collapse multiple slashes, remove trailing '/' except if the whole
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# path is '/', etc.
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self._normalize()
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return self
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if __name__ == "__main__":
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# The doctest setup below works, but for full test coverage, use the
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# unittest framework (it is set up to automatically run all doctests from
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# this module!).
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#
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# Hint: 'python3 -m unittest discover' from the TerraSync directory
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# should do the trick.
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import doctest
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doctest.testmod()
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