Function realpath

Lib/posixpath.py:389–513

Return the canonical path of the specified filename, eliminating any symbolic links encountered in the path.

(filename, /, *, strict=False)

# filesystem).

def realpath(filename, /, *, strict=False):
    """Return the canonical path of the specified filename, eliminating any
symbolic links encountered in the path."""
    filename = os.fspath(filename)
    if isinstance(filename, bytes):
        sep = b'/'
        curdir = b'.'
        pardir = b'..'
        getcwd = os.getcwdb
    else:
        sep = '/'
        curdir = '.'
        pardir = '..'
        getcwd = os.getcwd
    if strict is ALLOW_MISSING:
        ignored_error = FileNotFoundError
    elif strict is ALL_BUT_LAST:
        ignored_error = FileNotFoundError
    elif strict:
        ignored_error = ()
    else:
        ignored_error = OSError

    lstat = os.lstat
    readlink = os.readlink
    maxlinks = None

    # The stack of unresolved path parts. When popped, a special value of None
    # indicates that a symlink target has been resolved, and that the original
    # symlink path can be retrieved by popping again. The [::-1] slice is a
    # very fast way of spelling list(reversed(...)).
    rest = filename.rstrip(sep).split(sep)[::-1]

    # Number of unprocessed parts in 'rest'. This can differ from len(rest)
    # later, because 'rest' might contain markers for unresolved symlinks.
    part_count = len(rest)

    # The resolved path, which is absolute throughout this function.
    # Note: getcwd() returns a normalized and symlink-free path.
    path = sep if filename.startswith(sep) else getcwd()
    trailing_sep = filename.endswith(sep)

    # Mapping from symlink paths to *fully resolved* symlink targets. If a
    # symlink is encountered but not yet resolved, the value is None. This is
    # used both to detect symlink loops and to speed up repeated traversals of
    # the same links.
    seen = {}

    # Number of symlinks traversed. When the number of traversals is limited
    # by *maxlinks*, this is used instead of *seen* to detect symlink loops.
    link_count = 0

    while part_count:
        name = rest.pop()
        if name is None:
            # resolved symlink target
            seen[rest.pop()] = path
            continue