wiki:Documentation

ftputil -- a high-level FTP client library

Version: 3.1
Date: 2014-06-16
Summary:high-level FTP client library for Python
Keywords:FTP, ftplib substitute, virtual filesystem, pure Python
Author: Stefan Schwarzer <sschwarzer@sschwarzer.net>

Introduction

The ftputil module is a high-level interface to the ftplib module. The FTPHost objects generated from it allow many operations similar to those of os, os.path and shutil.

Example:

import ftputil

# Download some files from the login directory.
with ftputil.FTPHost("ftp.domain.com", "user", "password") as ftp_host:
    names = ftp_host.listdir(ftp_host.curdir)
    for name in names:
        if ftp_host.path.isfile(name):
            ftp_host.download(name, name)  # remote, local
    # Make a new directory and copy a remote file into it.
    ftp_host.mkdir("newdir")
    with ftp_host.open("index.html", "rb") as source:
        with ftp_host.open("newdir/index.html", "wb") as target:
            ftp_host.copyfileobj(source, target)  # similar to shutil.copyfileobj

Also, there are FTPHost.lstat and FTPHost.stat to request size and modification time of a file. The latter can also follow links, similar to os.stat. FTPHost.walk and FTPHost.path.walk work, too.

ftputil features

  • Method names are familiar from Python's os, os.path and shutil modules
  • Remote file system navigation (getcwd, chdir)
  • Upload and download files (upload, upload_if_newer, download, download_if_newer)
  • Time zone synchronization between client and server (needed for upload_if_newer and download_if_newer)
  • Create and remove directories (mkdir, makedirs, rmdir, rmtree) and remove files (remove)
  • Get information about directories, files and links (listdir, stat, lstat, exists, isdir, isfile, islink, abspath, split, join, dirname, basename etc.)
  • Iterate over remote file systems (walk)
  • Local caching of results from lstat and stat calls to reduce network access (also applies to exists, getmtime etc.).
  • Read files from and write files to remote hosts via file-like objects (FTPHost.open; the generated file-like objects have the familiar methods like read, readline, readlines, write, writelines and close. You can also iterate over these files line by line in a for loop.

Exception hierarchy

The exceptions are in the namespace of the ftputil.error module, e. g. ftputil.error.TemporaryError.

The exception classes are organized as follows:

FTPError
    FTPOSError(FTPError, OSError)
        PermanentError(FTPOSError)
            CommandNotImplementedError(PermanentError)
        TemporaryError(FTPOSError)
    FTPIOError(FTPError)
    InternalError(FTPError)
        InaccessibleLoginDirError(InternalError)
        ParserError(InternalError)
        RootDirError(InternalError)
        TimeShiftError(InternalError)

and are described here:

  • FTPError

    is the root of the exception hierarchy of the module.

  • FTPOSError

    is derived from OSError. This is for similarity between the os module and FTPHost objects. Compare

    try:
        os.chdir("nonexisting_directory")
    except OSError:
        ...
    

    with

    host = ftputil.FTPHost("host", "user", "password")
    try:
        host.chdir("nonexisting_directory")
    except OSError:
        ...
    

    Imagine a function

    def func(path, file):
        ...
    

    which works on the local file system and catches OSErrors. If you change the parameter list to

    def func(path, file, os=os):
        ...
    

    where os denotes the os module, you can call the function also as

    host = ftputil.FTPHost("host", "user", "password")
    func(path, file, os=host)
    

    to use the same code for both a local and remote file system. Another similarity between OSError and FTPOSError is that the latter holds the FTP server return code in the errno attribute of the exception object and the error text in strerror.

  • PermanentError

    is raised for 5xx return codes from the FTP server. This corresponds to ftplib.error_perm (though PermanentError and ftplib.error_perm are not identical).

  • CommandNotImplementedError

    indicates that an underlying command the code tries to use is not implemented. For an example, see the description of the FTPHost.chmod method.

  • TemporaryError

    is raised for FTP return codes from the 4xx category. This corresponds to ftplib.error_temp (though TemporaryError and ftplib.error_temp are not identical).

  • FTPIOError

    denotes an I/O error on the remote host. This appears mainly with file-like objects that are retrieved by calling FTPHost.open. Compare

    >>> try:
    ...     f = open("not_there")
    ... except IOError as obj:
    ...     print obj.errno
    ...     print obj.strerror
    ...
    2
    No such file or directory
    

    with

    >>> ftp_host = ftputil.FTPHost("host", "user", "password")
    >>> try:
    ...     f = ftp_host.open("not_there")
    ... except IOError as obj:
    ...     print obj.errno
    ...     print obj.strerror
    ...
    550
    550 not_there: No such file or directory.
    

    As you can see, both code snippets are similar. However, the error codes aren't the same.

  • InternalError

    subsumes exception classes for signaling errors due to limitations of the FTP protocol or the concrete implementation of ftputil.

  • InaccessibleLoginDirError

    This exception is raised if the directory in which "you" are placed upon login is not accessible, i. e. a chdir call with the directory as argument would fail.

  • ParserError

    is used for errors during the parsing of directory listings from the server. This exception is used by the FTPHost methods stat, lstat, and listdir.

  • RootDirError

    Because of the implementation of the lstat method it is not possible to do a stat call on the root directory /. If you know any way to do it, please let me know. :-)

    This problem does not affect stat calls on items in the root directory.

  • TimeShiftError

    is used to denote errors which relate to setting the time shift, for example trying to set a value which is no multiple of a full hour.

Directory and file names

Methods that take names of directories and files can take either byte strings (str on Python 2, bytes on Python 3) or unicode strings (unicode on Python 2, str on Python 3).

Byte strings will be sent to the FTP server as-is. Unicode strings will be encoded with the encoding returned from locale.getpreferredencoding. This is the same semantics as for locally used names in Python 3.

Methods that take and return a directory or file name will return the same string type as they're given. For example, if the argument to FTPHost.path.abspath is a byte string, you'll get a byte string back. This behavior is the same as for the local file system API in Python 2 and 3.

FTPHost objects

Construction

Basics

FTPHost instances can be generated with the following call:

ftp_host = ftputil.FTPHost(server, user, password, account,
                           session_factory=ftplib.FTP)

The first four parameters are strings with the same meaning as for the FTP class in the ftplib module.

FTPHost objects can also be used in a with statement:

import ftputil

with ftputil.FTPHost(server, user, password) as ftp_host:
    print ftp_host.listdir(ftp_host.curdir)

After the with block, the FTPHost instance and the associated FTP sessions will be closed automatically.

If something goes wrong during the FTPHost construction or in the body of the with statement, the instance is closed as well. Exceptions will be propagated (as with try ... finally).

Session factories

The keyword argument session_factory may be used to generate FTP connections with other factories than the default ftplib.FTP. For example, the standard library of Python 2.7 contains a class ftplib.FTP_TLS which extends ftplib.FTP to use an encrypted connection.

In fact, all positional and keyword arguments other than session_factory are passed to the factory to generate a new background session. This also happens for every remote file that is opened; see below.

This functionality of the constructor also allows to wrap ftplib.FTP objects to do something that wouldn't be possible with the ftplib.FTP constructor alone.

As an example, assume you want to connect to another than the default port, but ftplib.FTP only offers this by means of its connect method, not via its constructor. One solution is to use a custom class as a session factory:

import ftplib
import ftputil

EXAMPLE_PORT = 50001

class MySession(ftplib.FTP):

    def __init__(self, host, userid, password, port):
        """Act like ftplib.FTP's constructor but connect to another port."""
        ftplib.FTP.__init__(self)
        self.connect(host, port)
        self.login(userid, password)

# Try _not_ to use an _instance_ `MySession()` as factory, -
# use the class itself.
with ftputil.FTPHost(host, userid, password, port=EXAMPLE_PORT,
                     session_factory=MySession) as ftp_host:
    # Use `ftp_host` as usual.
    ...

On login, the format of the directory listings (needed for stat'ing files and directories) should be determined automatically. If not, please file a bug report.

For the most common uses you don't need to create your own session factory class though. The ftputil.session module has a function session_factory that can create session factories for a variety of parameters:

session_factory(base_class=ftplib.FTP,
                port=21,
                use_passive_mode=None,
                encrypt_data_channel=True,
                debug_level=None)

with

  • base_class is a base class to inherit a new session factory class from. By default, this is ftplib.FTP from the Python standard library.
  • port is the command channel port. The default is 21, used in most FTP server configurations.
  • use_passive_mode is either a boolean that determines whether passive mode should be used or None. None means to let the base class choose active or passive mode.
  • encrypt_data_channel defines whether to encrypt the data channel for secure connections. This is only supported for the base classes ftplib.FTP_TLS and M2Crypto.ftpslib.FTP_TLS, otherwise the the parameter is ignored.
  • debug_level sets the debug level for FTP session instances. The semantics is defined by the base class. For example, a debug level of 2 causes the most verbose output for Python's ftplib.FTP class.

All of these parameters can be combined. For example, you could use

import ftplib

import ftputil
import ftputil.session


my_session_factory = ftputil.session.session_factory(
                       base_class=ftpslib.FTP_TLS,
                       port=31,
                       encrypt_data_channel=True,
                       debug_level=2)

with ftputil.FTPHost(server, user, password,
                     session_factory=my_session_factory) as ftp_host:
    ...

to create and use a session factory derived from ftplib.FTP_TLS that connects on command channel 31, will encrypt the data channel and print output for debug level 2.

Note: Generally, you can achieve everything you can do with ftputil.session.session_factory with an explicit session factory as described at the start of this section. However, the class M2Crypto.ftpslib.FTP_TLS has a limitation so that you can't use it with ftputil out of the box. The function session_factory contains a workaround for this limitation. For details refer to this bug report.

Hidden files and directories

Whether ftputil sees "hidden" files and directories (usually files or directories whose names start with a dot) depends on the FTP server configuration. By default, ftputil uses the -a option in the FTP LIST command to find hidden files. However, the server may ignore this.

If using the -a option leads to problems, for example if an FTP server causes an exception, you may switch off the use of the option:

ftp_host = ftputil.FTPHost(server, user, password, account,
                           session_factory=ftplib.FTP)
ftp_host.use_list_a_option = False

FTPHost attributes and methods

Attributes

  • curdir, pardir, sep

    are strings which denote the current and the parent directory on the remote server. sep holds the path separator. Though RFC 959 (File Transfer Protocol) notes that these values may depend on the FTP server implementation, the Unix variants seem to work well in practice, even for non-Unix servers.

    Nevertheless, it's recommended that you don't hardcode these values for remote paths, but use FTPHost.path as you would use os.path to write platform-independent Python code for local filesystems. Keep in mind that most, but not all, arguments of FTPHost methods refer to remote directories or files. For example, in FTPHost.upload, the first argument is a local path and the second a remote path. Both of these should use their respective path separators.

Remote file system navigation

  • getcwd()

    returns the absolute current directory on the remote host. This method works like os.getcwd.

  • chdir(directory)

    sets the current directory on the FTP server. This resembles os.chdir, as you may have expected.

Uploading and downloading files

  • upload(source, target, callback=None)

    copies a local source file (given by a filename, i. e. a string) to the remote host under the name target. Both source and target may be absolute paths or relative to their corresponding current directory (on the local or the remote host, respectively).

    The file content is always transferred in binary mode.

    The callback, if given, will be invoked for each transferred chunk of data:

    callback(chunk)
    

    where chunk is a bytestring. An example usage of a callback method is to display a progress indicator.

  • download(source, target, callback=None)

    performs a download from the remote source file to a local target file. Both source and target are strings. See the description of upload for more details.

  • upload_if_newer(source, target, callback=None)

    is similar to the upload method. The only difference is that the upload is only invoked if the time of the last modification for the source file is more recent than that of the target file or the target doesn't exist at all. The check for the last modification time considers the precision of the timestamps and transfers a file "if in doubt". Consequently the code

    ftp_host.upload_if_newer("source_file", "target_file")
    time.sleep(10)
    ftp_host.upload_if_newer("source_file", "target_file")
    

    might upload the file again if the timestamp of the target file is precise up to a minute, which is typically the case because the remote datetime is determined by parsing a directory listing from the server. To avoid unnecessary transfers, wait at least a minute between calls of upload_if_newer for the same file. If it still seems that a file is uploaded unnecessarily (or not when it should), read the subsection on time shift settings.

    If an upload actually happened, the return value of upload_if_newer is a True, else False.

    Note that the method only checks the existence and/or the modification time of the source and target file; it doesn't compare any other file properties, say, the file size.

    This also means that if a transfer is interrupted, the remote file will have a newer modification time than the local file, and thus the transfer won't be repeated if upload_if_newer is used a second time. There are at least two possibilities after a failed upload:

    • use upload instead of upload_if_newer, or
    • remove the incomplete target file with FTPHost.remove, then use upload or upload_if_newer to transfer it again.
  • download_if_newer(source, target, callback=None)

    corresponds to upload_if_newer but performs a download from the server to the local host. Read the descriptions of download and upload_if_newer for more information. If a download actually happened, the return value is True, else False.

Time zone correction

If the client where ftputil runs and the server have a different understanding of their local times, this has to be taken into account for upload_if_newer and download_if_newer to work correctly.

Note that even if the client and the server are in the same time zone (or even on the same computer), the time shift value (see below) may be different from zero. For example, my computer is set to use local time whereas the server running on the very same host insists on using UTC time.

  • set_time_shift(time_shift)

    sets the so-called time shift value, measured in seconds. The time shift is the difference between the local time of the server and the local time of the client at a given moment, i. e. by definition

    time_shift = server_time - client_time
    

    Setting this value is important for upload_if_newer and download_if_newer to work correctly even if the time zone of the FTP server differs from that of the client. Note that the time shift value can be negative.

    If the time shift value is invalid, e. g. no multiple of a full hour or its absolute value larger than 24 hours, a TimeShiftError is raised.

    See also synchronize_times for a way to set the time shift with a simple method call.

  • time_shift()

    returns the currently-set time shift value. See set_time_shift above for its definition.

  • synchronize_times()

    synchronizes the local times of the server and the client, so that upload_if_newer and download_if_newer work as expected, even if the client and the server use different time zones. For this to work, all of the following conditions must be true:

    • The connection between server and client is established.
    • The client has write access to the directory that is current when synchronize_times is called.

    If you can't fulfill these conditions, you can nevertheless set the time shift value explicitly with set_time_shift. Trying to call synchronize_times if the above conditions aren't met results in a TimeShiftError exception.

Creating and removing directories

  • mkdir(path, [mode])

    makes the given directory on the remote host. This does not construct "intermediate" directories that don't already exist. The mode parameter is ignored; this is for compatibility with os.mkdir if an FTPHost object is passed into a function instead of the os module. See the explanation in the subsection Exception hierarchy.

  • makedirs(path, [mode])

    works similar to mkdir (see above), but also makes intermediate directories like os.makedirs. The mode parameter is only there for compatibility with os.makedirs and is ignored.

  • rmdir(path)

    removes the given remote directory. If it's not empty, raise a PermanentError.

  • rmtree(path, ignore_errors=False, onerror=None)

    removes the given remote, possibly non-empty, directory tree. The interface of this method is rather complex, in favor of compatibility with shutil.rmtree.

    If ignore_errors is set to a true value, errors are ignored. If ignore_errors is a false value and onerror isn't set, all exceptions occurring during the tree iteration and processing are raised. These exceptions are all of type PermanentError.

    To distinguish between different kinds of errors, pass in a callable for onerror. This callable must accept three arguments: func, path and exc_info. func is a bound method object, for example your_host_object.listdir. path is the path that was the recent argument of the respective method (listdir, remove, rmdir). exc_info is the exception info as it is gotten from sys.exc_info.

    The code of rmtree is taken from Python's shutil module and adapted for ftputil.

Local caching of file system information

Many of the above methods need access to the remote file system to obtain data on directories and files. To get the most recent data, each call to lstat, stat, exists, getmtime etc. would require to fetch a directory listing from the server, which can make the program very slow. This effect is more pronounced for operations which mostly scan the file system rather than transferring file data.

For this reason, ftputil by default saves the results from directory listings locally and reuses those results. This reduces network accesses and so speeds up the software a lot. However, since data is more rarely fetched from the server, the risk of obsolete data also increases. This will be discussed below.

Caching can be controlled -- if necessary at all -- via the stat_cache object in an FTPHost's namespace. For example, after calling

ftp_host = ftputil.FTPHost(host, user, password)

the cache can be accessed as ftp_host.stat_cache.

While ftputil usually manages the cache quite well, there are two possible reasons for modifying cache parameters.

The first is when the number of possible entries is too low. You may notice that when you are processing very large directories and the program becomes much slower than before. It's common for code to read a directory with listdir and then process the found directories and files. This can also happen implicitly by a call to FTPHost.walk. Since version 2.6 ftputil automatically increases the cache size if directories with more entries than the current maximum cache size are to be scanned. Most of the time, this works fine.

However, if you need access to stat data for several directories at the same time, you may need to increase the cache explicitly. This is done by the resize method:

ftp_host.stat_cache.resize(20000)

where the argument is the maximum number of lstat results to store (the default is 5000, in versions before 2.6 it was 1000). Note that each path on the server, e. g. "/home/schwa/some_dir", corresponds to a single cache entry. Methods like exists or getmtime all derive their results from a previously fetched lstat result.

The value 5000 above means that the cache will hold at most 5000 entries (unless increased automatically by an explicit or implicit listdir call, see above). If more are about to be stored, the entries which haven't been used for the longest time will be deleted to make place for newer entries.

The second possible reason to change the cache parameters is to avoid stale cache data. Caching is so effective because it reduces network accesses. This can also be a disadvantage if the file system data on the remote server changes after a stat result has been retrieved; the client, when looking at the cached stat data, will use obsolete information.

There are two potential ways to get such out-of-date stat data. The first happens when an FTPHost instance modifies a file path for which it has a cache entry, e. g. by calling remove or rmdir. Such changes are handled transparently; the path will be deleted from the cache. A different matter are changes unknown to the FTPHost object which inspects its cache. Obviously, for example, these are changes by programs running on the remote host. On the other hand, cache inconsistencies can also occur if two FTPHost objects change a file system simultaneously:

with (
  ftputil.FTPHost(server, user1, password1) as ftp_host1,
  ftputil.FTPHost(server, user1, password1) as ftp_host2
):
    stat_result1 = ftp_host1.stat("some_file")
    stat_result2 = ftp_host2.stat("some_file")
    ftp_host2.remove("some_file")
    # `ftp_host1` will still see the obsolete cache entry!
    print ftp_host1.stat("some_file")
    # Will raise an exception since an `FTPHost` object
    # knows of its own changes.
    print ftp_host2.stat("some_file")

At first sight, it may appear to be a good idea to have a shared cache among several FTPHost objects. After some thinking, this turns out to be very error-prone. For example, it won't help with different processes using ftputil. So, if you have to deal with concurrent write/read accesses to a server, you have to handle them explicitly.

The most useful tool for this is the invalidate method. In the example above, it could be used like this:

with (
  ftputil.FTPHost(server, user1, password1) as ftp_host1,
  ftputil.FTPHost(server, user1, password1) as ftp_host2
):
    stat_result1 = ftp_host1.stat("some_file")
    stat_result2 = ftp_host2.stat("some_file")
    ftp_host2.remove("some_file")
    # Invalidate using an absolute path.
    absolute_path = ftp_host1.path.abspath(
                      ftp_host1.path.join(ftp_host1.getcwd(), "some_file"))
    ftp_host1.stat_cache.invalidate(absolute_path)
    # Will now raise an exception as it should.
    print ftp_host1.stat("some_file")
    # Would raise an exception since an `FTPHost` object
    # knows of its own changes, even without `invalidate`.
    print ftp_host2.stat("some_file")

The method invalidate can be used on any absolute path, be it a directory, a file or a link.

By default, the cache entries (if not replaced by newer ones) are stored for an infinite time. That is, if you start your Python process using ftputil and let it run for three days a stat call may still access cache data that old. To avoid this, you can set the max_age attribute:

with ftputil.FTPHost(server, user, password) as ftp_host:
    ftp_host.stat_cache.max_age = 60 * 60  # = 3600 seconds

This sets the maximum age of entries in the cache to an hour. This means any entry older won't be retrieved from the cache but its data instead fetched again from the remote host and then again stored for up to an hour. To reset max_age to the default of unlimited age, i. e. cache entries never expire, use None as value.

If you are certain that the cache will be in the way, you can disable and later re-enable it completely with disable and enable:

with ftputil.FTPHost(server, user, password) as ftp_host:
    ftp_host.stat_cache.disable()
    ...
    ftp_host.stat_cache.enable()

During that time, the cache won't be used; all data will be fetched from the network. After enabling the cache again, its entries will be the same as when the cache was disabled, that is, entries won't get updated with newer data during this period. Note that even when the cache is disabled, the file system data in the code can become inconsistent:

with ftputil.FTPHost(server, user, password) as ftp_host:
    ftp_host.stat_cache.disable()
    if ftp_host.path.exists("some_file"):
        mtime = ftp_host.path.getmtime("some_file")

In that case, the file some_file may have been removed by another process between the calls to exists and getmtime!

Iteration over directories

  • walk(top, topdown=True, onerror=None, followlinks=False)

    iterates over a directory tree, similar to os.walk. Actually, FTPHost.walk uses the code from Python with just the necessary modifications, so see the linked documentation.

  • path.walk(path, func, arg)

    Similar to os.path.walk, the walk method in FTPHost.path can be used, though FTPHost.walk is probably easier to use.

Other methods

  • close()

    closes the connection to the remote host. After this, no more interaction with the FTP server is possible with this FTPHost object. Usually you don't need to close an FTPHost instance with close if you set up the instance in a with statement.

  • rename(source, target)

    renames the source file (or directory) on the FTP server.

  • chmod(path, mode)

    sets the access mode (permission flags) for the given path. The mode is an integer as returned for the mode by the stat and lstat methods. Be careful: Usually, mode values are written as octal numbers, for example 0755 to make a directory readable and writable for the owner, but not writable for the group and others. If you want to use such octal values, rely on Python's support for them:

    ftp_host.chmod("some_directory", 0o755)
    

    Not all FTP servers support the chmod command. In case of an exception, how do you know if the path doesn't exist or if the command itself is invalid? If the FTP server complies with RFC 959, it should return a status code 502 if the SITE CHMOD command isn't allowed. ftputil maps this special error response to a CommandNotImplementedError which is derived from PermanentError.

    So you need to code like this:

    with ftputil.FTPHost(server, user, password) as ftp_host:
        try:
            ftp_host.chmod("some_file", 0o644)
        except ftputil.error.CommandNotImplementedError:
            # `chmod` not supported
            ...
        except ftputil.error.PermanentError:
            # Possibly a non-existent file
            ...
    

    Because the CommandNotImplementedError is more specific, you have to test for it first.

  • copyfileobj(source, target, length=64*1024)

    copies the contents from the file-like object source to the file-like object target. The only difference to shutil.copyfileobj is the default buffer size. Note that arbitrary file-like objects can be used as arguments (e. g. local files, remote FTP files).

    However, the interfaces of source and target have to match; the string type read from source must be an accepted string type when written to target. For example, if you open source in Python 3 as a local text file and target as a remote file object in binary mode, the transfer will fail since source.read gives unicode strings whereas target.write only accepts byte strings.

    See File-like objects for the construction and use of remote file-like objects.

  • set_parser(parser)

    sets a custom parser for FTP directories. Note that you have to pass in a parser instance, not the class.

    An extra section shows how to write own parsers if the default parsers in ftputil don't work for you.

  • keep_alive()

    attempts to keep the connection to the remote server active in order to prevent timeouts from happening. This method is primarily intended to keep the underlying FTP connection of an FTPHost object alive while a file is uploaded or downloaded. This will require either an extra thread while the upload or download is in progress or calling keep_alive from a callback function.

    The keep_alive method won't help if the connection has already timed out. In this case, a ftputil.error.TemporaryError is raised.

    If you want to use this method, keep in mind that FTP servers define a timeout for a reason. A timeout prevents running out of server connections because of clients that never disconnect on their own.

    Note that the keep_alive method does not affect the "hidden" FTP child connections established by FTPHost.open (see section FTPHost instances vs. FTP connections for details). You can't use keep_alive to avoid a timeout in a stalling transfer like this:

    with ftputil.FTPHost(server, userid, password) as ftp_host:
        with ftp_host.open("some_remote_file", "rb") as fobj:
            data = fobj.read(100)
            # _Futile_ attempt to avoid file connection timeout.
            for i in xrange(15):
                time.sleep(60)
                ftp_host.keep_alive()
            # Will raise an `ftputil.error.TemporaryError`.
            data += fobj.read()
    

File-like objects

Construction

Basics

FTPFile objects are returned by a call to FTPHost.open; never use the FTPFile constructor directly.

The API of remote file-like objects are is modeled after the API of the io module in Python 3, which has also been backported to Python 2.6 and 2.7.

  • FTPHost.open(path, mode="r", buffering=None, encoding=None, errors=None, newline=None)

    returns a file-like object that refers to the path on the remote host. This path may be absolute or relative to the current directory on the remote host (this directory can be determined with the getcwd method). As with local file objects, the default mode is "r", i. e. reading text files. Valid modes are "r", "rb", "w", and "wb".

    If a file is opened in binary mode, you must not specify an encoding. On the other hand, if you open a file in text mode, an encoding is used. By default, this is the return value of locale.getpreferredencoding, but you can (and probably should) specify a distinct encoding.

    If you open a file in binary mode, the read and write operations use byte strings (str in Python 2, bytes in Python 3). That is, read operations return byte strings and write operations only accept byte strings.

    Similarly, text files always work with unicode strings (unicode in Python 2, str in Python 3). Here, read operations return unicode strings and write operations only accept unicode strings.

    The arguments errors and newline have the same semantics as in io.open. The argument buffering currently is ignored. It's only there for compatibility with the io.open interface.

Note that the semantics of "text mode" has changed fundamentally from ftputil 2.8 and earlier. Previously, "text mode" implied converting newline characters to \r\n when writing remote files and converting newlines to \n when reading remote files. This is in line with the "text mode" notion of FTP command line clients. Now, "text mode" follows the semantics in Python's io module.

FTPHost.open can also be used in a with statement:

import ftputil

with ftputil.FTPHost(...) as ftp_host:
    ...
    with ftp_host.open("new_file", "w", encoding="utf8") as fobj:
        fobj.write("This is some text.")

At the end of the with block, the remote file will be closed automatically.

If something goes wrong during the construction of the file or in the body of the with statement, the file will be closed as well. Exceptions will be propagated as with try ... finally.

Attributes and methods

The methods

close()
read([count])
readline([count])
readlines()
write(data)
writelines(string_sequence)

and the attribute closed have the same semantics as for file objects of a local disk file system. The iterator protocol is supported as well, i. e. you can use a loop to read a file line by line:

with ftputil.FTPHost(server, user, password) as ftp_host:
    with ftp_host.open("some_file") as input_file:
        for line in input_file:
            # Do something with the line, e. g.
            print line.strip().replace("ftplib", "ftputil")

For more on file objects, see the section File objects in the Python Library Reference.

FTPHost instances vs. FTP connections

This section explains why keeping an FTPHost instance "alive" without timing out sometimes isn't trivial. If you always finish your FTP operations in time, you don't need to read this section.

The file transfer protocol is a stateful protocol. That means an FTP connection always is in a certain state. Each of these states can only change to certain other states under certain conditions triggered by the client or the server.

One of the consequences is that a single FTP connection can't be used at the same time, say, to transfer data on the FTP data channel and to create a directory on the remote host.

For example, consider this:

>>> import ftplib
>>> ftp = ftplib.FTP(server, user, password)
>>> ftp.pwd()
'/'
>>> # Start transfer. `CONTENTS` is a text file on the server.
>>> socket = ftp.transfercmd("RETR CONTENTS")
>>> socket
<socket._socketobject object at 0x7f801a6386e0>
>>> ftp.pwd()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python2.7/ftplib.py", line 578, in pwd
    return parse257(resp)
  File "/usr/lib64/python2.7/ftplib.py", line 842, in parse257
    raise error_reply, resp
ftplib.error_reply: 226-File successfully transferred
226 0.000 seconds (measured here), 5.60 Mbytes per second
>>>

Note that ftp is a single FTP connection, represented by an ftplib.FTP instance, not an ftputil.FTPHost instance.

On the other hand, consider this:

>>> import ftputil
>>> ftp_host = ftputil.FTPHost(server, user, password)
>>> ftp_host.getcwd()
>>> fobj = ftp_host.open("CONTENTS")
>>> fobj
<ftputil.file.FTPFile object at 0x7f8019d3aa50>
>>> ftp_host.getcwd()
u'/'
>>> fobj.readline()
u'Contents of FTP test directory\n'
>>> fobj.close()
>>>

To be able to start a file transfer (i. e. open a remote file for reading or writing) and still be able to use other FTP commands, ftputil uses a trick. For every remote file, ftputil creates a new FTP connection, called a child connection in the ftputil source code. (Actually, FTP connections belonging to closed remote files are re-used if they haven't timed out yet.)

In most cases this approach isn't noticable by code using ftputil. However, the nice abstraction of dealing with a single FTP connection falls apart if one of the child connections times out. For example, if you open a remote file and work only with the initial "main" connection to navigate the file system, the FTP connection for the remote file may eventually time out.

While it's often relatively easy to prevent the "main" connection from timing out it's unfortunately practically impossible to do this for a remote file connection (apart from transferring some data, of course). For this reason, FTPHost.keep_alive affects only the main connection. Child connections may still time out if they're idle for too long.

Some more details:

  • A kind of "straightforward" way of keeping the main connection alive would be to call ftp_host.getcwd(). However, this doesn't work because ftputil caches the current directory and returns it without actually contacting the server. That's the main reason why there's a keep_alive method since it calls pwd on the FTP connection (i. e. the session object), which isn't a public attribute.
  • Some servers define not only an idle timeout but also a transfer timeout. This means the connection times out unless there's some transfer on the data channel for this connection. So ftputil's keep_alive doesn't prevent this timeout, but an ftp_host.listdir(ftp_host.curdir) call should do it. However, this transfers the data for the whole directory listing which might take some time if the directory has many entries.

Bottom line: If you can, you should organize your FTP actions so that you finish everything before a timeout happens.

Writing directory parsers

ftputil recognizes the two most widely-used FTP directory formats, Unix and MS style, and adjusts itself automatically. Almost every FTP server uses one of these formats.

However, if your server uses a format which is different from the two provided by ftputil, you can plug in a custom parser with a single method call and have ftputil use this parser.

For this, you need to write a parser class by inheriting from the class Parser in the ftputil.stat module. Here's an example:

import ftputil.error
import ftputil.stat

class XyzParser(ftputil.stat.Parser):
    """
    Parse the default format of the FTP server of the XYZ
    corporation.
    """

    def parse_line(self, line, time_shift=0.0):
        """
        Parse a `line` from the directory listing and return a
        corresponding `StatResult` object. If the line can't
        be parsed, raise `ftputil.error.ParserError`.

        The `time_shift` argument can be used to fine-tune the
        parsing of dates and times. See the class
        `ftputil.stat.UnixParser` for an example.
        """
        # Split the `line` argument and examine it further; if
        # something goes wrong, raise an `ftputil.error.ParserError`.
        ...
        # Make a `StatResult` object from the parts above.
        stat_result = ftputil.stat.StatResult(...)
        # `_st_name`, `_st_target` and `_st_mtime_precision` are optional.
        stat_result._st_name = ...
        stat_result._st_target = ...
        stat_result._st_mtime_precision = ...
        return stat_result

    # Define `ignores_line` only if the default in the base class
    # doesn't do enough!
    def ignores_line(self, line):
        """
        Return a true value if the line should be ignored. For
        example, the implementation in the base class handles
        lines like "total 17". On the other hand, if the line
        should be used for stat'ing, return a false value.
        """
        is_total_line = super(XyzParser, self).ignores_line(line)
        my_test = ...
        return is_total_line or my_test

A StatResult object is similar to the value returned by os.stat and is usually built with statements like

stat_result = StatResult(
                (st_mode, st_ino, st_dev, st_nlink, st_uid,
                 st_gid, st_size, st_atime, st_mtime, st_ctime))
stat_result._st_name = ...
stat_result._st_target = ...
stat_result._st_mtime_precision = ...

with the arguments of the StatResult constructor described in the following table.

Index Attribute os.stat type StatResult type Notes
0 st_mode int int  
1 st_ino long long  
2 st_dev long long  
3 st_nlink int int  
4 st_uid int str usually only available as string
5 st_gid int str usually only available as string
6 st_size long long  
7 st_atime int/float float  
8 st_mtime int/float float  
9 st_ctime int/float float  
- _st_name - str file name without directory part
- _st_target - str link target (may be absolute or relative)
- _st_mtime_precision - int st_mtime precision in seconds

If you can't extract all the desirable data from a line (for example, the MS format doesn't contain any information about the owner of a file), set the corresponding values in the StatResult instance to None.

Parser classes can use several helper methods which are defined in the class Parser:

  • parse_unix_mode parses strings like "drwxr-xr-x" and returns an appropriate st_mode integer value.
  • parse_unix_time returns a float number usable for the st_...time values by parsing arguments like "Nov"/"23"/"02:33" or "May"/"26"/"2005". Note that the method expects the timestamp string already split at whitespace.
  • parse_ms_time parses arguments like "10-23-01"/"03:25PM" and returns a float number like from time.mktime. Note that the method expects the timestamp string already split at whitespace.

Additionally, there's an attribute _month_numbers which maps lowercase three-letter month abbreviations to integers.

For more details, see the two "standard" parsers UnixParser and MSParser in the module ftputil/stat.py.

To actually use the parser, call the method set_parser of the FTPHost instance.

If you can't write a parser or don't want to, please ask on the ftputil mailing list. Possibly someone has already written a parser for your server or can help with it.

FAQ / Tips and tricks

Where can I get the latest version?

See the download page. Announcements will be sent to the mailing list. Announcements on major updates will also be posted to the newsgroup comp.lang.python.announce .

Is there a mailing list on ftputil?

Yes, please visit http://ftputil.sschwarzer.net/mailinglist to subscribe or read the archives.

Though you can technically post without subscribing first I can't recommend it: The mails from non-subscribers have to be approved by me and because the arriving mails contain lots of spam, I rarely go through these mails.

I found a bug! What now?

Before reporting a bug, make sure that you already read this manual and tried the latest version of ftputil. There the bug might have already been fixed.

Please see http://ftputil.sschwarzer.net/issuetrackernotes for guidelines on entering a bug in ftputil's ticket system. If you are unsure if the behaviour you found is a bug or not, you should write to the ftputil mailing list. In either case you must not include confidential information (user id, password, file names, etc.) in the problem report! Be careful!

Does ftputil support SSL/TLS?

ftputil has no built-in SSL/TLS support.

On the other hand, there are two ways to get TLS support with ftputil:

  • In Python 2.7 and Python 3.2 and up, the ftplib library has a class FTP_TLS that you can use for the session_factory keyword argument in the FTPHost constructor. You can't use the class directly though if you need additional setup code in comparison to ftplib.FTP, for example calling prot_p, to secure the data connection. On the other hand, ftputil.session.session_factory can be used to create a custom session factory.

    If you have other requirements that session_factory can't fulfill, you may create your own session factory by inheriting from ftplib.FTP_TLS:

    import ftplib
    
    import ftputil
    
    
    class FTPTLSSession(ftplib.FTP_TLS):
    
        def __init__(self, host, user, password):
            ftplib.FTP_TLS.__init__(self)
            self.connect(host, port)
            self.login(user, password)
            # Set up encrypted data connection.
            self.prot_p()
            ...
    
    # Note the `session_factory` parameter. Pass the class, not
    # an instance.
    with ftputil.FTPHost(server, user, password,
                         session_factory=FTPTLSSession) as ftp_host:
        # Use `ftp_host` as usual.
        ...
    
  • If you need to work with Python 2.6, you can use the ftpslib.FTP_TLS class from the M2Crypto project. Again, you can't use the class directly but need to use ftputil.session.session_factory or a recipe similar to that above.

    Unfortunately, M2Crypto.ftpslib.FTP_TLS (at least in version 0.22.3) doesn't work correctly if you pass unicode strings to its methods. Since ftputil does exactly that at some point (even if you used byte strings in ftputil calls) you need a workaround in the session factory class:

    import M2Crypto
    
    import ftputil
    import ftputil.tool
    
    
    class M2CryptoSession(M2Crypto.ftpslib.FTP_TLS):
    
        def __init__(self, host, user, password):
            M2Crypto.ftpslib.FTP_TLS.__init__(self)
            # Change the port number if needed.
            self.connect(host, 21)
            self.auth_tls()
            self.login(user, password)
            self.prot_p()
            self._fix_socket()
            ...
    
        def _fix_socket(self):
            """
            Change the socket object so that arguments to `sendall`
            are converted to byte strings before being used.
            """
            original_sendall = self.sock.sendall
            # Bound method, therefore no `self` argument.
            def sendall(data):
                data = ftputil.tool.as_bytes(data)
                return original_sendall(data)
            self.sock.sendall = sendall
    
    # Note the `session_factory` parameter. Pass the class, not
    # an instance.
    with ftputil.FTPHost(server, user, password,
                         session_factory=M2CryptoSession) as ftp_host:
        # Use `ftp_host` as usual.
        ...
    

    That said, session_factory has this workaround built in, so normally you don't need to define the session factory yourself!

How do I connect to a non-default port?

By default, an instantiated FTPHost object connects on the usual FTP port. If you have to use a different port, refer to the section Session factories.

How can I debug an FTP connection problem?

You can do this with a session factory. See Session factories.

If you want to change the debug level only temporarily after the connection is established, you can reach the session object as the _session attribute of the FTPHost instance and call _session.set_debuglevel. Note that the _session attribute should only be accessed for debugging. Calling arbitrary ftplib.FTP methods on the session object may cause bugs!

Conditional upload/download to/from a server in a different time zone

You may find that ftputil uploads or downloads files unnecessarily, or not when it should. This can happen when the FTP server is in a different time zone than the client on which ftputil runs. Please see the section on time zone correction. It may even be sufficient to call synchronize_times.

When I use ftputil, all I get is a ParserError exception

The FTP server you connect to may use a directory format that ftputil doesn't understand. You can either write and plug in an own parser or ask on the mailing list for help.

I don't find an answer to my problem in this document

Please send an email with your problem report or question to the ftputil mailing list, and we'll see what we can do for you. :-)

Bugs and limitations

  • ftputil needs at least Python 2.6 to work.
  • Whether ftputil "sees" "hidden" directory and file names (i. e. names starting with a dot) depends on the configuration of the FTP server. See Hidden files and directories for details.
  • Due to the implementation of lstat it can not return a sensible value for the root directory / though stat'ing entries in the root directory isn't a problem. If you know an implementation that can do this, please let me know. The root directory is handled appropriately in FTPHost.path.exists/isfile/isdir/islink, though.
  • In multithreaded programs, you can have each thread use one or more FTPHost instances as long as no instance is shared with other threads.
  • Currently, it is not possible to continue an interrupted upload or download. Contact me if this causes problems for you.
  • There's exactly one cache for lstat results for each FTPHost object, i. e. there's no sharing of cache results determined by several FTPHost objects. See Local caching of file system information for the reasons.

Files

If not overwritten via installation options, the ftputil files reside in the ftputil package. There's also documentation in reStructuredText and in HTML format. The locations of these files after installation is system-dependent.

The files test_*.py and mock_ftplib.py are for unit-testing. If you only use ftputil, i. e. don't modify it, you can delete these files.

References

Authors

ftputil is written by Stefan Schwarzer <sschwarzer@sschwarzer.net>, in part based on suggestions from users.

The original lrucache module was written by Evan Prodromou <evan@prodromou.name>.

Feedback is appreciated. :-)