path: root/fs/base.py

#!/usr/bin/env python
"""
fs.base
=======

This module defines the most basic filesystem abstraction, the FS class.
Instances of FS represent a filesystem containing files and directories
that can be queried and manipulated.  To implement a new kind of filesystem,
start by sublcassing the base FS class.

"""

__all__ = ['DummyLock',
           'silence_fserrors',
           'NullFile',
           'synchronize',
           'FS',
           'flags_to_mode',
           'NoDefaultMeta']

import os.path
import shutil
import fnmatch
import datetime
import time
try:
    import threading
except ImportError:
    import dummy_threading as threading

from fs.path import *
from fs.errors import *
from fs.local_functools import wraps

class DummyLock(object):
    """A dummy lock object that doesn't do anything.

    This is used as a placeholder when locking is disabled.  We can't
    directly use the Lock class from the dummy_threading module, since
    it attempts to sanity-check the sequence of acquire/release calls
    in a way that breaks when real threading is available.
    
    """

    def acquire(self,blocking=1):
        """Acquiring a DummyLock always succeeds."""
        return 1

    def release(self):
        """Releasing a DummyLock always succeeds."""
        pass
    
    def __enter__(self):
        pass
    
    def __exit__(self, *args):
        pass


def silence_fserrors(f, *args, **kwargs):
    """Perform a function call and return None if FSError is thrown

    :param f: Function to call
    :param args: Parameters to f
    :param kwargs: Keyword parameters to f

    """
    try:
        return f(*args, **kwargs)
    except FSError:
        return None


class NoDefaultMeta(object):
    """A singleton used to signify that there is no default for getmeta"""
    pass


class NullFile(object):
    """A NullFile is a file object that has no functionality.

    Null files are returned by the 'safeopen' method in FS objects when the
    file doesn't exist. This can simplify code by negating the need to check
    if a file exists, or handling exceptions.

    """
    def __init__(self):
        self.closed = False

    def flush(self):
        pass

    def __iter__(self):
        return self

    def next(self):
        raise StopIteration

    def readline(self, *args, **kwargs):
        return ""

    def close(self):
        self.closed = True

    def read(self, size=None):
        return ""

    def seek(self, *args, **kwargs):
        pass

    def tell(self):
        return 0

    def truncate(self, *args, **kwargs):
        return 0

    def write(self, data):
        pass

    def writelines(self, *args, **kwargs):
        pass


def synchronize(func):
    """Decorator to synchronize a method on self._lock."""
    @wraps(func)
    def acquire_lock(self, *args, **kwargs):
        self._lock.acquire()
        try:
            return func(self, *args, **kwargs)
        finally:
            self._lock.release()
    return acquire_lock


class FS(object):
    """The base class for Filesystem abstraction objects.
    An instance of a class derived from FS is an abstraction on some kind of filesytem, such as the OS filesystem or a zip file.

    """
    
    _meta = {}

    def __init__(self, thread_synchronize=False):
        """The base class for Filesystem objects.

        :param thread_synconize: If True, a lock object will be created for the object, otherwise a dummy lock will be used.
        :type thread_synchronize: bool
        
        """
        
        super(FS, self).__init__()
        self.closed = False
        self.thread_synchronize = thread_synchronize
        if thread_synchronize:
            self._lock = threading.RLock()
        else:
            self._lock = DummyLock()

    def __del__(self):
        if not getattr(self, 'closed', True):
            self.close()
    
    def __enter__(self):
        return self
    
    def __exit__(self, type, value, traceback):        
        self.close()

    def cachehint(self, enabled):
        """Recommends the use of caching. Implementations are free to use or
            ignore this value.

        :param enabled: If True the implementation is permitted to aggressively cache directory
            structure / file information. Caching such information speeds up most operations,
            particularly for network based filesystems. The downside of caching is that
            changes made to directories or files outside of this interface may not be picked up.

        """
        pass
    # Depricating cache_hint in favour of no underscore version, for consistency
    cache_hint = cachehint 

    def close(self):
        """Close the filesystem. This will perform any shutdown related
        operations required. This method will be called automatically when
        the filesystem object is garbage collected, but it is good practice
        to call it explicitly so that any attached resourced are freed when they
        are no longer required.
        
        """
        self.closed = True

    def __getstate__(self):
        #  Locks can't be pickled, so instead we just indicate the
        #  type of lock that should be there.  None == no lock,
        #  True == a proper lock, False == a dummy lock.
        state = self.__dict__.copy()
        lock = state.get("_lock",None)
        if lock is not None:
            if isinstance(lock,threading._RLock):
                state["_lock"] = True
            else:
                state["_lock"] = False
        return state

    def __setstate__(self,state):
        self.__dict__.update(state)        
        lock = state.get("_lock")
        if lock is not None:
            if lock:
                self._lock = threading.RLock()
            else:
                self._lock = DummyLock()

    def getmeta(self, meta_name, default=NoDefaultMeta):
        """Retrieve a meta value associated with an FS object.

        Meta values are a way for an FS implementation to report potentially
        useful information associated with the file system.
        
        A meta key is a lower case string with no spaces. Meta keys may also
        be grouped in namespaces in a dotted notation, e.g. 'atomic.namespaces'.                
        FS implementations aren't obliged to return any meta values, but the
        following are common:
        
         * *read_only* True if the file system cannot be modified
         * *network* True if the file system requires network access
         * *unicode_paths* True if the file system supports unicode paths
         * *case_insensitive_paths* True if the file system ignores the case of paths        
         * *atomic.makedir* True if making a directory is an atomic operation
         * *atomic.rename* True if rename is an atomic operation, (and not implemented as a copy followed by a delete)
         * *atomic.setcontents* True if the implementation supports setting the contents of a file as an atomic operation (without opening a file)
         
        The following are less common:
        
         * *free_space* The free space (in bytes) available on the file system   
         * *total_space* The total space (in bytes) available on the file system   
        
        FS implementations may expose non-generic meta data through a self-named namespace. e.g. 'somefs.some_meta'
        
        Since no meta value is guaranteed to exist, it is advisable to always supply a
        default value to `getmeta`.   
        
        :param meta_name: The name of the meta value to retrieve
        :param default: An option default to return, if the meta value isn't present
        :raises NoMetaError: If specified meta value is not present, and there is no default        
        
        """         
        if meta_name not in self._meta:
            if default is not NoDefaultMeta:
                return default
            raise NoMetaError(meta_name=meta_name)        
        return self._meta[meta_name]
        
    def hasmeta(self, meta_name):
        """Check that a meta value is supported
        
        :param meta_name: The name of a meta value to check
        :rtype: bool
        
        """
        try:
            self.getmeta(meta_name)
        except NoMetaError:
            return False
        return True        

    def getsyspath(self, path, allow_none=False):
        """Returns the system path (a path recognised by the OS) if one is present.

        If the path does not map to a system path (and `allow_none` is False)
        then a NoSysPathError exception is thrown.  Otherwise, the system
        path will be returned as a unicode string.

        :param path: a path within the filesystem
        :param allow_none: if True, this method will return None when there is no system path,
            rather than raising NoSysPathError
        :type allow_none: bool
        :raises NoSysPathError: if the path does not map on to a system path, and allow_none is set to False (default)
        :rtype: unicode
        
        """
        if not allow_none:
            raise NoSysPathError(path=path)
        return None

    def hassyspath(self, path):
        """Check if the path maps to a system path (a path recognised by the OS).

        :param path: path to check
        :returns: True if `path` maps to a system path
        :rtype: bool  
              
        """
        return self.getsyspath(path, allow_none=True) is not None
    
    def getpathurl(self, path, allow_none=False):
        """Returns a url that corresponds to the given path, if one exists.
        
        If the path does not have an equivalent URL form (and allow_none is False)
        then a NoPathURLError exception is thrown. Otherwise the URL will be
        returns as an unicode string.
        
        :param path: a path within the filesystem
        :param allow_none: if true, this method can return None if there is no
            URL form of the given path
        :type allow_none: bool
        :raises NoPathURLError: If no URL form exists, and allow_none is False (the default)
        :rtype: unicode 
        
        """
        if not allow_none:
            raise NoPathURLError(path=path)
        return None
    
    def haspathurl(self, path):
        """Check if the path has an equivalent URL form

        :param path: path to check
        :returns: True if `path` has a URL form
        :rtype: bool
                
        """
        return self.getpathurl(path, allow_none=True) is not None

    def open(self, path, mode="r", **kwargs):
        """Open a the given path as a file-like object.

        :param path: a path to file that should be opened
        :param mode: mode of file to open, identical to the mode string used
            in 'file' and 'open' builtins
        :param kwargs: additional (optional) keyword parameters that may
            be required to open the file        
        :rtype: a file-like object
        
        """
        raise UnsupportedError("open file")

    def safeopen(self, path, mode="r", **kwargs):
        """Like :py:meth:`~fs.base.FS.open`, but returns a :py:class:`~fs.base.NullFile` if the file could not be opened.

        A NullFile is a dummy file which has all the methods of a file-like object,
        but contains no data.

        :param path: a path to file that should be opened
        :param mode: mode of file to open, identical to the mode string used
            in 'file' and 'open' builtins
        :param kwargs: additional (optional) keyword parameters that may
            be required to open the file        
        :rtype: a file-like object

        """
        try:
            f = self.open(path, mode, **kwargs)
        except ResourceNotFoundError:
            return NullFile()
        return f

    def exists(self, path):
        """Check if a path references a valid resource.

        :param path: A path in the filessystem
        :rtype: bool
        
        """
        return self.isfile(path) or self.isdir(path)

    def isdir(self, path):
        """Check if a path references a directory.

        :param path: a path in the filessystem
        :rtype: bool

        """
        raise UnsupportedError("check for directory")

    def isfile(self, path):
        """Check if a path references a file.

        :param path: a path in the filessystem
        :rtype: bool

        """
        raise UnsupportedError("check for file")

    def __iter__(self):
        """ Iterates over paths returned by :py:meth:`~fs.base.listdir` method with default params. """
        for f in self.listdir():
            yield f

    def listdir(self, path="./",
                      wildcard=None,
                      full=False,
                      absolute=False,
                      dirs_only=False,
                      files_only=False):
        """Lists the the files and directories under a given path.

        The directory contents are returned as a list of unicode paths.

        :param path: root of the path to list
        :type path: string
        :param wildcard: Only returns paths that match this wildcard
        :type wildcard: string containing a wildcard, or a callable that accepts a path and returns a boolean
        :param full: returns full paths (relative to the root)
        :type full: bool
        :param absolute: returns absolute paths (paths beginning with /)
        :type absolute: bool
        :param dirs_only: if True, only return directories
        :type dirs_only: bool
        :param files_only: if True, only return files
        :type files_only: bool        
        :rtype: iterable of paths

        :raises `fs.errors.ResourceNotFoundError`: if the path is not found
        :raises `fs.errror.ResourceInvalidError`: if the path exists, but is not a directory

        """
        raise UnsupportedError("list directory")

    def listdirinfo(self, path="./",
                          wildcard=None,
                          full=False,
                          absolute=False,
                          dirs_only=False,
                          files_only=False):
        """Retrieves a list of paths and path info under a given path.

        This method behaves like listdir() but instead of just returning
        the name of each item in the directory, it returns a tuple of the
        name and the info dict as returned by getinfo.

        This method may be more efficient than calling
        :py:meth:`~fs.base.FS.getinfo` on each individual item returned by :py:meth:`~fs.base.FS.listdir`, particularily
        for network based filesystems.

        :param path: root of the path to list
        :param wildcard: filter paths that match this wildcard
        :param dirs_only: only retrive directories
        :type dirs_only: bool
        :param files_only: only retrieve files
        :type files_only: bool

        :raises `fs.errors.ResourceNotFoundError`: If the path is not found
        :raises `fs.errors.ResourceInvalidError`: If the path exists, but is not a directory

        """
        path = normpath(path)
        def getinfo(p):
            try:
                if full or absolute:
                    return self.getinfo(p)
                else:
                    return self.getinfo(pathjoin(path,p))
            except FSError:
                return {}

        return [(p, getinfo(p))
                    for p in self.listdir(path,
                                          wildcard=wildcard,
                                          full=full,
                                          absolute=absolute,
                                          dirs_only=dirs_only,
                                          files_only=files_only)]

    def _listdir_helper(self, path,
                              entries,
                              wildcard=None,
                              full=False,
                              absolute=False,
                              dirs_only=False,
                              files_only=False):
        """A helper method called by listdir method that applies filtering.

        Given the path to a directory and a list of the names of entries within
        that directory, this method applies the semantics of the listdir()
        keyword arguments. An appropriately modified and filtered list of
        directory entries is returned.
        
        """
        if dirs_only and files_only:
            raise ValueError("dirs_only and files_only can not both be True")

        if wildcard is not None:
            if not callable(wildcard):
                wildcard_re = re.compile(fnmatch.translate(wildcard))
                wildcard = lambda fn:bool (wildcard_re.match(fn))          
            entries = [p for p in entries if wildcard(p)]

        if dirs_only:
            entries = [p for p in entries if self.isdir(pathjoin(path, p))]
        elif files_only:
            entries = [p for p in entries if self.isfile(pathjoin(path, p))]

        if full:
            entries = [pathjoin(path, p) for p in entries]
        elif absolute:
            entries = [abspath(pathjoin(path, p)) for p in entries]

        return entries

    def ilistdir(self, path="./",
                       wildcard=None,
                       full=False,
                       absolute=False,
                       dirs_only=False,
                       files_only=False):
        """Generator yielding the files and directories under a given path.

        This method behaves identically to :py:meth:`fs.base.FS.listdir` but returns an generator
        instead of a list.  Depending on the filesystem this may be more
        efficient than calling :py:meth:`fs.base.FS.listdir` and iterating over the resulting list.
        
        """
        return iter(self.listdir(path,
                                 wildcard=wildcard,
                                 full=full,
                                 absolute=absolute,
                                 dirs_only=dirs_only,
                                 files_only=files_only))

    def ilistdirinfo(self, path="./",
                           wildcard=None,
                           full=False,
                           absolute=False,
                           dirs_only=False,
                           files_only=False):
        """Generator yielding paths and path info under a given path.

        This method behaves identically to :py:meth:`~fs.base.listdirinfo` but returns an generator
        instead of a list.  Depending on the filesystem this may be more
        efficient than calling :py:meth:`~fs.base.listdirinfo` and iterating over the resulting
        list.
        
        """
        return iter(self.listdirinfo(path,
                                     wildcard,
                                     full,
                                     absolute,
                                     dirs_only,
                                     files_only))

    def makedir(self, path, recursive=False, allow_recreate=False):
        """Make a directory on the filesystem.

        :param path: path of directory
        :param recursive: if True, any intermediate directories will also be created
        :type recursive: bool
        :param allow_recreate: if True, re-creating a directory wont be an error
        :type allow_create: bool
        
        :raises `fs.errors.DestinationExistsError`: if the path is already a directory, and allow_recreate is False
        :raises `fs.errors.ParentDirectoryMissingError`: if a containing directory is missing and recursive is False
        :raises `fs.errors.ResourceInvalidError`: if a path is an existing file

        """
        raise UnsupportedError("make directory")

    def remove(self, path):
        """Remove a file from the filesystem.

        :param path: Path of the resource to remove

        :raises `fs.errors.ResourceNotFoundError`: if the path does not exist
        :raises `fs.errors.ResourceInvalidError`: if the path is a directory

        """
        raise UnsupportedError("remove resource")

    def removedir(self, path, recursive=False, force=False):
        """Remove a directory from the filesystem

        :param path: path of the directory to remove
        :param recursive: if True, empty parent directories will be removed
        :type recursive: bool
        :param force: if True, any directory contents will be removed
        :type force: bool

        :raises `fs.errors.ResourceNotFoundError`: if the path does not exist
        :raises `fs.errors.ResourceInvalidError`: if the path is not a directory
        :raises `fs.errors.DirectoryNotEmptyError`: if the directory is not empty and force is False
        
        """
        raise UnsupportedError("remove directory")

    def rename(self, src, dst):
        """Renames a file or directory

        :param src: path to rename
        :param dst: new name
        
        """
        raise UnsupportedError("rename resource")

    @convert_os_errors
    def settimes(self, path, accessed_time=None, modified_time=None):
        """Set the accessed time and modified time of a file
        
        :param path: path to a file
        :param accessed_time: a datetime object the file was accessed (defaults to current time) 
        :param modified_time: a datetime object the file was modified (defaults to current time)
        
        """
                
        sys_path = self.getsyspath(path, allow_none=True)
        if sys_path is not None:            
            now = datetime.datetime.now()
            if accessed_time is None:
                accessed_time = now
            if modified_time is None:
                modified_time = now                         
            accessed_time = int(time.mktime(accessed_time.timetuple()))
            modified_time = int(time.mktime(modified_time.timetuple()))
            os.utime(sys_path, (accessed_time, modified_time))
            return True
        else:
            raise UnsupportedError("settimes")
                   
    def getinfo(self, path):
        """Returns information for a path as a dictionary. The exact content of
        this dictionary will vary depending on the implementation, but will
        likely include a few common values. The following values will be found
        in info dictionaries for most implementations:
        
         * "size" - Number of bytes used to store the file or directory
         * "created_time" - A datetime object containing the time the resource was created
         * "accessed_time" - A datetime object containing the time the resource was last accessed  
         * "modified_time" - A datetime object containing the time the resource was modified

        :param path: a path to retrieve information for
        :rtype: dict
        
        """
        raise UnsupportedError("get resource info")

    def desc(self, path):
        """Returns short descriptive text regarding a path. Intended mainly as
        a debugging aid.

        :param path: A path to describe
        :rtype: str
        
        """
        if not self.exists(path):
            return ''
        try:
            sys_path = self.getsyspath(path)
        except NoSysPathError:
            return "No description available"        
        return sys_path
        

    def getcontents(self, path):
        """Returns the contents of a file as a string.

        :param path: A path of file to read
        :rtype: str
        :returns: file contents
        """
        f = None
        try:
            f = self.open(path, "rb")
            contents = f.read()
            return contents
        finally:
            if f is not None:
                f.close()

    def setcontents(self, path, data, chunk_size=1024*64):
        """A convenience method to create a new file from a string or file-like object

        :param path: a path of the file to create
        :param data: a string or a file-like object containing the contents for the new file
        :param chunk_size: Number of bytes to read in a chunk, if the implementation has to resort to a read / copy loop
        
        """
        
        if not data:
            self.createfile(path)
        else:
            f = None
            try:
                f = self.open(path, 'wb')
                if hasattr(data, "read"):
                    read = data.read
                    write = f.write
                    chunk = read(chunk_size)
                    while chunk:
                        write(chunk)
                        chunk = read(chunk_size)
                else:
                    f.write(data)
                if hasattr(f, 'flush'):
                    f.flush()
            finally:
                if f is not None:
                    f.close()
                    
    def setcontents_async(self,
                          path,
                          data,
                          chunk_size=1024*64,
                          progress_callback=None,
                          finished_callback=None,
                          error_callback=None):
        """Create a new file from a string or file-like object asynchronously
        
        This method returns a `threading.Event` object. Call the `wait` method on the event object
        to block until all data has been written, or simply ignore it.        
        
        :param path: a path of the file to create
        :param data: a string or a file-like object containing the contents for the new file
        :param chunk_size: Number of bytes to read and write in a chunk
        :param progress_callback: A function that is called periodically
            with the number of bytes written.
        :param finished_callback: A fuction that is called when all data has been written
        :param error_callback: A function that is called with an exception
            object if any error occurrs during the copy process.
        :returns: An event object that is set when the copy is complete, call
            the `wait` method of this object to block until the data is written
            
        """                
        
        if progress_callback is None:
            progress_callback = lambda bytes_written:None                        
        
        def do_setcontents():        
            try:        
                f = None
                try:
                    f = self.open(path, 'wb')
                    progress_callback(0)                    
                    
                    if hasattr(data, "read"):
                        bytes_written = 0
                        read = data.read
                        write = f.write
                        chunk = read(chunk_size)
                        while chunk:
                            write(chunk)
                            bytes_written += len(chunk)
                            progress_callback(bytes_written)
                            chunk = read(chunk_size)                        
                    else:                        
                        f.write(data)                                    
                        progress_callback(len(data))
                        
                    if finished_callback is not None:
                        finished_callback()
                    
                finally:
                    if f is not None:
                        f.close()
                        
            except Exception, e:
                if error_callback is not None:
                    error_callback(e)
            
            finally:
                finished_event.set()
        
        finished_event = threading.Event()        
        threading.Thread(target=do_setcontents).start()
        return finished_event
                    
        
    def createfile(self, path, wipe=False):
        """Creates an empty file if it doesn't exist
        
        :param path: path to the file to create
        :param wipe: If True, the contents of the file will be erased 
        
        """
        if not wipe and self.isfile(path):
            return
            
        f = None
        try:
            f = self.open(path, 'w')
        finally:
            if f is not None:
                f.close()
            

    def opendir(self, path):
        """Opens a directory and returns a FS object representing its contents.

        :param path: path to directory to open
        :rtype: An FS object
        
        """
        
        #if path in ('', '/'):
        #    return self
        from fs.wrapfs.subfs import SubFS
        if not self.exists(path):
            raise ResourceNotFoundError(path)
        return SubFS(self, path)

    def walk(self,
             path="/",
             wildcard=None,
             dir_wildcard=None,
             search="breadth",
             ignore_errors=False):
        """Walks a directory tree and yields the root path and contents.
        Yields a tuple of the path of each directory and a list of its file
        contents.

        :param path: root path to start walking
        :param wildcard: if given, only return files that match this wildcard
        :type wildcard: a string containing a wildcard (e.g. `*.txt`) or a callable that takes the file path and returns a boolean
        :param dir_wildcard: if given, only walk directories that match the wildcard
        :type dir_wildcard: a string containing a wildcard (e.g. `*.txt`) or a callable that takes the directory name and returns a boolean
        :param search: a string dentifying the method used to walk the directories. There are two such methods:
        
             * "breadth" yields paths in the top directories first
             * "depth" yields the deepest paths first
                          
        :param ignore_errors: ignore any errors reading the directory

        """        
        
        if wildcard is None:
            wildcard = lambda f:True
        elif not callable(wildcard):
            wildcard_re = re.compile(fnmatch.translate(wildcard))
            wildcard = lambda fn:bool (wildcard_re.match(fn))
            
        if dir_wildcard is None:
            dir_wildcard = lambda f:True
        elif not callable(dir_wildcard):
            dir_wildcard_re = re.compile(fnmatch.translate(dir_wildcard))
            dir_wildcard = lambda fn:bool (dir_wildcard_re.match(fn))                    
        
        def listdir(path, *args, **kwargs):
            if ignore_errors:
                try:
                    return self.listdir(path, *args, **kwargs)
                except:
                    return []
            else:
                return self.listdir(path, *args, **kwargs)
        
        if search == "breadth":
            
            dirs = [path]
            while dirs:
                current_path = dirs.pop()
                paths = []
                try:
                    for filename in listdir(current_path):
                        path = pathjoin(current_path, filename)
                        if self.isdir(path):                        
                            if dir_wildcard(path):
                                dirs.append(path)                        
                        else:                        
                            if wildcard(filename):
                                paths.append(filename)
                except ResourceNotFoundError:
                    # Could happen if another thread / process deletes something whilst we are walking
                    pass
                            
                yield (current_path, paths)

        elif search == "depth":

            def recurse(recurse_path):
                try:
                    for path in listdir(recurse_path, wildcard=dir_wildcard, full=True, dirs_only=True):
                        for p in recurse(path):
                            yield p
                except ResourceNotFoundError:
                    # Could happen if another thread / process deletes something whilst we are walking
                    pass
                yield (recurse_path, self.listdir(recurse_path, wildcard=wildcard, files_only=True))

            for p in recurse(path):
                yield p
                
        else:
            raise ValueError("Search should be 'breadth' or 'depth'")

    def walkfiles(self,
                  path="/",
                  wildcard=None,
                  dir_wildcard=None,
                  search="breadth",
                  ignore_errors=False ):
        """Like the 'walk' method, but just yields file paths.

        :param path: root path to start walking
        :param wildcard: if given, only return files that match this wildcard
        :type wildcard: A string containing a wildcard (e.g. `*.txt`) or a callable that takes the file path and returns a boolean
        :param dir_wildcard: if given, only walk directories that match the wildcard
        :type dir_wildcard: A string containing a wildcard (e.g. `*.txt`) or a callable that takes the directory name and returns a boolean
        :param search: same as walk method
        :param ignore_errors: ignore any errors reading the directory
        
        """
        for path, files in self.walk(path, wildcard=wildcard, dir_wildcard=dir_wildcard, search=search, ignore_errors=ignore_errors):
            for f in files:
                yield pathjoin(path, f)

    def walkdirs(self,
                 path="/",
                 wildcard=None,
                 search="breadth",
                 ignore_errors=False):
        """Like the 'walk' method but yields directories.

        :param path: root path to start walking
        :param wildcard: if given, only return dictories that match this wildcard
        :type wildcard: A string containing a wildcard (e.g. `*.txt`) or a callable that takes the directory name and returns a boolean
        :param search: same as the walk method
        :param ignore_errors: ignore any errors reading the directory
        
        """
        for p, _files in self.walk(path, dir_wildcard=wildcard, search=search, ignore_errors=ignore_errors):
            yield p


    def getsize(self, path):
        """Returns the size (in bytes) of a resource.

        :param path: a path to the resource
        :rtype: integer
        :returns: the size of the file
        
        """
        info = self.getinfo(path)
        size = info.get('size', None)
        if size is None:
            raise OperationFailedError("get size of resource", path)
        return size
    
    def copy(self, src, dst, overwrite=False, chunk_size=1024*64):
        """Copies a file from src to dst.

        :param src: the source path
        :param dst: the destination path
        :param overwrite: if True, then an existing file at the destination may
            be overwritten; If False then DestinationExistsError
            will be raised.
        :param chunk_size: size of chunks to use if a simple copy is required
            (defaults to 64K).
            
        """

        if not self.isfile(src):
            if self.isdir(src):
                raise ResourceInvalidError(src,msg="Source is not a file: %(path)s")
            raise ResourceNotFoundError(src)
        if not overwrite and self.exists(dst):
            raise DestinationExistsError(dst)

        src_syspath = self.getsyspath(src, allow_none=True)
        dst_syspath = self.getsyspath(dst, allow_none=True)

        if src_syspath is not None and dst_syspath is not None:
            self._shutil_copyfile(src_syspath, dst_syspath)
        else:
            src_file = None            
            try:
                src_file = self.open(src, "rb")                
                self.setcontents(dst, src_file, chunk_size=chunk_size)                
            finally:
                if src_file is not None:
                    src_file.close()                
    
    @classmethod
    @convert_os_errors    
    def _shutil_copyfile(cls, src_syspath, dst_syspath):
        try:
            shutil.copyfile(src_syspath, dst_syspath)
        except IOError, e:
            #  shutil reports ENOENT when a parent directory is missing
            if getattr(e,"errno",None) == 2:
                if not os.path.exists(dirname(dst_syspath)):
                    raise ParentDirectoryMissingError(dst_syspath)
            raise
        
    @classmethod
    @convert_os_errors
    def _shutil_movefile(cls, src_syspath, dst_syspath):
        shutil.move(src_syspath, dst_syspath)
        
    
    def move(self, src, dst, overwrite=False, chunk_size=16384):
        """moves a file from one location to another.

        :param src: source path
        :param dst: destination path
        :param overwrite: if True, then an existing file at the destination path
            will be silently overwritten; if False then an exception
            will be raised in this case.
        :param overwrite: When True the destination will be overwritten (if it exists),
            otherwise a DestinationExistsError will be thrown 
        :type overwrite: bool
        :param chunk_size: Size of chunks to use when copying, if a simple copy
            is required
        :type chunk_size: integer
        
        """

        src_syspath = self.getsyspath(src, allow_none=True)
        dst_syspath = self.getsyspath(dst, allow_none=True)

        #  Try to do an os-level rename if possible.
        #  Otherwise, fall back to copy-and-remove.
        if src_syspath is not None and dst_syspath is not None:
            if not os.path.isfile(src_syspath):
                if os.path.isdir(src_syspath):
                    raise ResourceInvalidError(src, msg="Source is not a file: %(path)s")
                raise ResourceNotFoundError(src)
            if not overwrite and os.path.exists(dst_syspath):
                raise DestinationExistsError(dst)
            try:
                os.rename(src_syspath, dst_syspath)
                return
            except OSError:
                pass
        self.copy(src, dst, overwrite=overwrite, chunk_size=chunk_size)
        self.remove(src)
    
    def movedir(self, src, dst, overwrite=False, ignore_errors=False, chunk_size=16384):
        """moves a directory from one location to another.

        :param src: source directory path
        :param dst: destination directory path
        :param overwrite: if True then any existing files in the destination
            directory will be overwritten
        :param ignore_errors: if True then this method will ignore FSError
            exceptions when moving files
        :param chunk_size: size of chunks to use when copying, if a simple copy
            is required
            
        """
        if not self.isdir(src):
            if self.isfile(src):
                raise ResourceInvalidError(src, msg="Source is not a directory: %(path)s")
            raise ResourceNotFoundError(src)
        if not overwrite and self.exists(dst):
            raise DestinationExistsError(dst)

        src_syspath = self.getsyspath(src, allow_none=True)
        dst_syspath = self.getsyspath(dst, allow_none=True)

        if src_syspath is not None and dst_syspath is not None:
            try:
                os.rename(src_syspath,dst_syspath)
                return
            except OSError:
                pass

        def movefile_noerrors(src, dst, **kwargs):
            try:
                return self.move(src, dst, **kwargs)
            except FSError:
                return
        if ignore_errors:
            movefile = movefile_noerrors
        else:
            movefile = self.move

        src = abspath(src)
        dst = abspath(dst)

        if dst:
            self.makedir(dst, allow_recreate=overwrite)

        for dirname, filenames in self.walk(src, search="depth"):

            dst_dirname = relpath(frombase(src, abspath(dirname)))
            dst_dirpath = pathjoin(dst, dst_dirname)
            self.makedir(dst_dirpath, allow_recreate=True, recursive=True)

            for filename in filenames:

                src_filename = pathjoin(dirname, filename)
                dst_filename = pathjoin(dst_dirpath, filename)
                movefile(src_filename, dst_filename, overwrite=overwrite, chunk_size=chunk_size)

            self.removedir(dirname)
    
    def copydir(self, src, dst, overwrite=False, ignore_errors=False, chunk_size=16384):
        """copies a directory from one location to another.

        :param src: source directory path
        :param dst: destination directory path
        :param overwrite: if True then any existing files in the destination
            directory will be overwritten
        :type overwrite: bool
        :param ignore_errors: if True, exceptions when copying will be ignored
        :type ignore_errors: bool
        :param chunk_size: size of chunks to use when copying, if a simple copy
            is required (defaults to 16K)
            
        """
        if not self.isdir(src):
            raise ResourceInvalidError(src, msg="Source is not a directory: %(path)s")
        def copyfile_noerrors(src, dst, **kwargs):
            try:
                return self.copy(src, dst, **kwargs)
            except FSError:
                return
        if ignore_errors:
            copyfile = copyfile_noerrors
        else:
            copyfile = self.copy

        src = abspath(src)
        dst = abspath(dst)

        if not overwrite and self.exists(dst):
            raise DestinationExistsError(dst)

        if dst:
            self.makedir(dst, allow_recreate=overwrite)

        for dirname, filenames in self.walk(src):

            dst_dirname = relpath(frombase(src, abspath(dirname)))
            dst_dirpath = pathjoin(dst, dst_dirname)
            self.makedir(dst_dirpath, allow_recreate=True, recursive=True)

            for filename in filenames:

                src_filename = pathjoin(dirname, filename)
                dst_filename = pathjoin(dst_dirpath, filename)
                copyfile(src_filename, dst_filename, overwrite=overwrite, chunk_size=chunk_size)

    def isdirempty(self, path):
        """Check if a directory is empty (contains no files or sub-directories)

        :param path: a directory path
        :rtype: bool
        
        """
        path = normpath(path)
        iter_dir = iter(self.listdir(path))
        try:
            iter_dir.next()
        except StopIteration:
            return True
        return False

    def makeopendir(self, path, recursive=False):
        """makes a directory (if it doesn't exist) and returns an FS object for
        the newly created directory.

        :param path: path to the new directory
        :param recursive: if True any intermediate directories will be created

        """

        self.makedir(path, allow_recreate=True, recursive=recursive)
        dir_fs = self.opendir(path)
        return dir_fs

    def printtree(self, max_levels=5):
        """Prints a tree structure of the FS object to the console
        
        :param max_levels: The maximum sub-directories to display, defaults to
            5. Set to None for no limit 
        
        """
        from fs.utils import print_fs                
        print_fs(self, max_levels=max_levels)
    tree = printtree
    
    def browse(self):
        """Displays the FS tree in a graphical window (requires wxWidgets)"""
        from fs.browsewin import browse
        browse(self)

    def getmmap(self, path, read_only=False, copy=False):
        """Returns a mmap object for this path.
        
        See http://docs.python.org/library/mmap.html for more details on the mmap module.
        
        :param path: A path on this filesystem
        :param read_only: If True, the mmap may not be modified
        :param copy: If False then changes wont be written back to the file
        :raises NoMMapError: Only paths that have a syspath can be opened as a mmap 
         
        """        
        syspath = self.getsyspath(path, allow_none=True)
        if syspath is None:
            raise NoMMapError(path)
        
        try:
            import mmap            
        except ImportError:
            raise NoMMapError(msg="mmap not supported")
        
        if read_only:
            f = open(syspath, 'rb')
            access = mmap.ACCESS_READ
        else:
            if copy:
                f = open(syspath, 'rb')
                access = mmap.ACCESS_COPY
            else:
                f = open(syspath, 'r+b')
                access = mmap.ACCESS_WRITE      
                  
        m = mmap.mmap(f.fileno(), 0, access=access)
        return m


def flags_to_mode(flags):
    """Convert an os.O_* flag bitmask into an FS mode string."""    
    if flags & os.O_WRONLY:
        if flags & os.O_TRUNC:
            mode = "w"
        elif flags & os.O_APPEND:
            mode = "a"
        else:
            mode = "r+"
    elif flags & os.O_RDWR:
        if flags & os.O_TRUNC:
            mode = "w+"
        elif flags & os.O_APPEND:
            mode = "a+"
        else:
            mode = "r+"
    else:
        mode = "r"    
    if flags & os.O_EXCL:
        mode += "x"
    return mode