454 lines
14 KiB
Python
454 lines
14 KiB
Python
"""Common operations on Posix pathnames.
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Instead of importing this module directly, import os and refer to
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this module as os.path. The "os.path" name is an alias for this
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module on Posix systems; on other systems (e.g. Mac, Windows),
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os.path provides the same operations in a manner specific to that
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platform, and is an alias to another module (e.g. macpath, ntpath).
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Some of this can actually be useful on non-Posix systems too, e.g.
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for manipulation of the pathname component of URLs.
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"""
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import os
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import stat
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__all__ = ["normcase","isabs","join","splitdrive","split","splitext",
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"basename","dirname","commonprefix","getsize","getmtime",
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"getatime","getctime","islink","exists","lexists","isdir","isfile",
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"ismount","walk","expanduser","expandvars","normpath","abspath",
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"samefile","sameopenfile","samestat",
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"curdir","pardir","sep","pathsep","defpath","altsep","extsep",
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"devnull","realpath","supports_unicode_filenames"]
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# strings representing various path-related bits and pieces
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curdir = '.'
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pardir = '..'
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extsep = '.'
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sep = '/'
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pathsep = ':'
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defpath = ':/bin:/usr/bin'
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altsep = None
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devnull = '/dev/null'
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# Normalize the case of a pathname. Trivial in Posix, string.lower on Mac.
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# On MS-DOS this may also turn slashes into backslashes; however, other
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# normalizations (such as optimizing '../' away) are not allowed
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# (another function should be defined to do that).
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def normcase(s):
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"""Normalize case of pathname. Has no effect under Posix"""
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return s
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# Return whether a path is absolute.
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# Trivial in Posix, harder on the Mac or MS-DOS.
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def isabs(s):
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"""Test whether a path is absolute"""
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return s.startswith('/')
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# Join pathnames.
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# Ignore the previous parts if a part is absolute.
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# Insert a '/' unless the first part is empty or already ends in '/'.
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def join(a, *p):
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"""Join two or more pathname components, inserting '/' as needed"""
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path = a
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for b in p:
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if b.startswith('/'):
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path = b
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elif path == '' or path.endswith('/'):
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path += b
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else:
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path += '/' + b
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return path
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# Split a path in head (everything up to the last '/') and tail (the
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# rest). If the path ends in '/', tail will be empty. If there is no
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# '/' in the path, head will be empty.
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# Trailing '/'es are stripped from head unless it is the root.
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def split(p):
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"""Split a pathname. Returns tuple "(head, tail)" where "tail" is
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everything after the final slash. Either part may be empty."""
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i = p.rfind('/') + 1
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head, tail = p[:i], p[i:]
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if head and head != '/'*len(head):
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head = head.rstrip('/')
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return head, tail
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# Split a path in root and extension.
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# The extension is everything starting at the last dot in the last
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# pathname component; the root is everything before that.
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# It is always true that root + ext == p.
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def splitext(p):
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"""Split the extension from a pathname. Extension is everything from the
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last dot to the end. Returns "(root, ext)", either part may be empty."""
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i = p.rfind('.')
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if i<=p.rfind('/'):
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return p, ''
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else:
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return p[:i], p[i:]
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# Split a pathname into a drive specification and the rest of the
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# path. Useful on DOS/Windows/NT; on Unix, the drive is always empty.
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def splitdrive(p):
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"""Split a pathname into drive and path. On Posix, drive is always
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empty."""
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return '', p
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# Return the tail (basename) part of a path.
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def basename(p):
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"""Returns the final component of a pathname"""
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return split(p)[1]
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# Return the head (dirname) part of a path.
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def dirname(p):
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"""Returns the directory component of a pathname"""
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return split(p)[0]
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# Return the longest prefix of all list elements.
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def commonprefix(m):
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"Given a list of pathnames, returns the longest common leading component"
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if not m: return ''
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s1 = min(m)
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s2 = max(m)
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n = min(len(s1), len(s2))
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for i in xrange(n):
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if s1[i] != s2[i]:
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return s1[:i]
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return s1[:n]
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# Get size, mtime, atime of files.
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def getsize(filename):
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"""Return the size of a file, reported by os.stat()."""
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return os.stat(filename).st_size
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def getmtime(filename):
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"""Return the last modification time of a file, reported by os.stat()."""
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return os.stat(filename).st_mtime
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def getatime(filename):
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"""Return the last access time of a file, reported by os.stat()."""
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return os.stat(filename).st_atime
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def getctime(filename):
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"""Return the metadata change time of a file, reported by os.stat()."""
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return os.stat(filename).st_ctime
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# Is a path a symbolic link?
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# This will always return false on systems where os.lstat doesn't exist.
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def islink(path):
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"""Test whether a path is a symbolic link"""
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try:
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st = os.lstat(path)
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except (os.error, AttributeError):
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return False
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return stat.S_ISLNK(st.st_mode)
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# Does a path exist?
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# This is false for dangling symbolic links.
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def exists(path):
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"""Test whether a path exists. Returns False for broken symbolic links"""
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try:
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st = os.stat(path)
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except os.error:
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return False
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return True
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# Being true for dangling symbolic links is also useful.
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def lexists(path):
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"""Test whether a path exists. Returns True for broken symbolic links"""
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try:
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st = os.lstat(path)
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except os.error:
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return False
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return True
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# Is a path a directory?
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# This follows symbolic links, so both islink() and isdir() can be true
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# for the same path.
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def isdir(path):
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"""Test whether a path is a directory"""
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try:
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st = os.stat(path)
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except os.error:
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return False
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return stat.S_ISDIR(st.st_mode)
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# Is a path a regular file?
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# This follows symbolic links, so both islink() and isfile() can be true
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# for the same path.
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def isfile(path):
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"""Test whether a path is a regular file"""
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try:
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st = os.stat(path)
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except os.error:
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return False
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return stat.S_ISREG(st.st_mode)
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# Are two filenames really pointing to the same file?
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def samefile(f1, f2):
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"""Test whether two pathnames reference the same actual file"""
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s1 = os.stat(f1)
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s2 = os.stat(f2)
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return samestat(s1, s2)
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# Are two open files really referencing the same file?
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# (Not necessarily the same file descriptor!)
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def sameopenfile(fp1, fp2):
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"""Test whether two open file objects reference the same file"""
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s1 = os.fstat(fp1)
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s2 = os.fstat(fp2)
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return samestat(s1, s2)
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# Are two stat buffers (obtained from stat, fstat or lstat)
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# describing the same file?
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def samestat(s1, s2):
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"""Test whether two stat buffers reference the same file"""
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return s1.st_ino == s2.st_ino and \
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s1.st_dev == s2.st_dev
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# Is a path a mount point?
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# (Does this work for all UNIXes? Is it even guaranteed to work by Posix?)
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def ismount(path):
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"""Test whether a path is a mount point"""
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try:
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s1 = os.stat(path)
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s2 = os.stat(join(path, '..'))
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except os.error:
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return False # It doesn't exist -- so not a mount point :-)
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dev1 = s1.st_dev
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dev2 = s2.st_dev
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if dev1 != dev2:
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return True # path/.. on a different device as path
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ino1 = s1.st_ino
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ino2 = s2.st_ino
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if ino1 == ino2:
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return True # path/.. is the same i-node as path
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return False
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# Directory tree walk.
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# For each directory under top (including top itself, but excluding
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# '.' and '..'), func(arg, dirname, filenames) is called, where
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# dirname is the name of the directory and filenames is the list
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# of files (and subdirectories etc.) in the directory.
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# The func may modify the filenames list, to implement a filter,
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# or to impose a different order of visiting.
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def walk(top, func, arg):
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"""Directory tree walk with callback function.
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For each directory in the directory tree rooted at top (including top
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itself, but excluding '.' and '..'), call func(arg, dirname, fnames).
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dirname is the name of the directory, and fnames a list of the names of
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the files and subdirectories in dirname (excluding '.' and '..'). func
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may modify the fnames list in-place (e.g. via del or slice assignment),
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and walk will only recurse into the subdirectories whose names remain in
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fnames; this can be used to implement a filter, or to impose a specific
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order of visiting. No semantics are defined for, or required of, arg,
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beyond that arg is always passed to func. It can be used, e.g., to pass
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a filename pattern, or a mutable object designed to accumulate
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statistics. Passing None for arg is common."""
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try:
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names = os.listdir(top)
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except os.error:
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return
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func(arg, top, names)
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for name in names:
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name = join(top, name)
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try:
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st = os.lstat(name)
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except os.error:
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continue
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if stat.S_ISDIR(st.st_mode):
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walk(name, func, arg)
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# Expand paths beginning with '~' or '~user'.
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# '~' means $HOME; '~user' means that user's home directory.
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# If the path doesn't begin with '~', or if the user or $HOME is unknown,
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# the path is returned unchanged (leaving error reporting to whatever
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# function is called with the expanded path as argument).
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# See also module 'glob' for expansion of *, ? and [...] in pathnames.
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# (A function should also be defined to do full *sh-style environment
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# variable expansion.)
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def expanduser(path):
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"""Expand ~ and ~user constructions. If user or $HOME is unknown,
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do nothing."""
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if not path.startswith('~'):
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return path
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i = path.find('/', 1)
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if i < 0:
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i = len(path)
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if i == 1:
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if 'HOME' not in os.environ:
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import pwd
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userhome = pwd.getpwuid(os.getuid()).pw_dir
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else:
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userhome = os.environ['HOME']
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else:
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import pwd
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try:
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pwent = pwd.getpwnam(path[1:i])
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except KeyError:
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return path
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userhome = pwent.pw_dir
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userhome = userhome.rstrip('/')
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return userhome + path[i:]
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# Expand paths containing shell variable substitutions.
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# This expands the forms $variable and ${variable} only.
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# Non-existent variables are left unchanged.
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_varprog = None
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def expandvars(path):
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"""Expand shell variables of form $var and ${var}. Unknown variables
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are left unchanged."""
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global _varprog
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if '$' not in path:
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return path
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if not _varprog:
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import re
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_varprog = re.compile(r'\$(\w+|\{[^}]*\})')
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i = 0
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while True:
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m = _varprog.search(path, i)
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if not m:
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break
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i, j = m.span(0)
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name = m.group(1)
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if name.startswith('{') and name.endswith('}'):
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name = name[1:-1]
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if name in os.environ:
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tail = path[j:]
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path = path[:i] + os.environ[name]
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i = len(path)
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path += tail
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else:
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i = j
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return path
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# Normalize a path, e.g. A//B, A/./B and A/foo/../B all become A/B.
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# It should be understood that this may change the meaning of the path
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# if it contains symbolic links!
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def normpath(path):
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"""Normalize path, eliminating double slashes, etc."""
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if path == '':
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return '.'
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initial_slashes = path.startswith('/')
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# POSIX allows one or two initial slashes, but treats three or more
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# as single slash.
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if (initial_slashes and
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path.startswith('//') and not path.startswith('///')):
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initial_slashes = 2
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comps = path.split('/')
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new_comps = []
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for comp in comps:
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if comp in ('', '.'):
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continue
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if (comp != '..' or (not initial_slashes and not new_comps) or
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(new_comps and new_comps[-1] == '..')):
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new_comps.append(comp)
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elif new_comps:
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new_comps.pop()
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comps = new_comps
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path = '/'.join(comps)
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if initial_slashes:
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path = '/'*initial_slashes + path
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return path or '.'
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def abspath(path):
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"""Return an absolute path."""
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if not isabs(path):
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path = join(os.getcwd(), path)
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return normpath(path)
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# Return a canonical path (i.e. the absolute location of a file on the
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# filesystem).
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def realpath(filename):
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"""Return the canonical path of the specified filename, eliminating any
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symbolic links encountered in the path."""
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if isabs(filename):
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bits = ['/'] + filename.split('/')[1:]
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else:
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bits = [''] + filename.split('/')
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for i in range(2, len(bits)+1):
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component = join(*bits[0:i])
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# Resolve symbolic links.
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if islink(component):
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resolved = _resolve_link(component)
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if resolved is None:
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# Infinite loop -- return original component + rest of the path
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return abspath(join(*([component] + bits[i:])))
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else:
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newpath = join(*([resolved] + bits[i:]))
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return realpath(newpath)
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return abspath(filename)
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def _resolve_link(path):
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"""Internal helper function. Takes a path and follows symlinks
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until we either arrive at something that isn't a symlink, or
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encounter a path we've seen before (meaning that there's a loop).
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"""
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paths_seen = []
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while islink(path):
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if path in paths_seen:
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# Already seen this path, so we must have a symlink loop
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return None
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paths_seen.append(path)
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# Resolve where the link points to
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resolved = os.readlink(path)
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if not isabs(resolved):
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dir = dirname(path)
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path = normpath(join(dir, resolved))
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else:
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path = normpath(resolved)
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return path
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supports_unicode_filenames = False
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