ftplib substitute, virtual filesystem, pure Python
Author: Stefan Schwarzer
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
- Method names are familiar from Python’s
shutilmodules. For example, use
os.path.jointo join paths for a local file system and
ftp_host.path.jointo join paths for a remote FTP file system.
- Remote file system navigation (
- Upload and download files (
- Time zone synchronization between client and server (needed for
- Create and remove directories (
rmtree) and remove files (
- Get information about directories, files and links (
- Iterate over remote file systems (
- Local caching of results from
statcalls to reduce network access (also applies to
- Read files from and write files to remote hosts via file-like
FTPHost.open; the generated file-like objects have the familiar methods like
close. You can also iterate over these files line by line in a
The exceptions are in the namespace of the
ftputil.error module, e.g.
The exception classes are organized as follows:
FTPError FTPOSError(FTPError, OSError) PermanentError(FTPOSError) CommandNotImplementedError(PermanentError) TemporaryError(FTPOSError) FTPIOError(FTPError) InternalError(FTPError) InaccessibleLoginDirError(InternalError) NoEncodingError(InternalError) ParserError(InternalError) RootDirError(InternalError) TimeShiftError(InternalError)
and are described here:
is the root of the exception hierarchy of the module.
is derived from
OSError. This is for similarity between the os module and
try: os.chdir("nonexisting_directory") except OSError: ...
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): ...
osmodule, 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
FTPOSErroris that the latter holds the FTP server return code in the
errnoattribute of the exception object and the error text in
is raised for 5xx return codes from the FTP server. This corresponds to
ftplib.error_permare not identical).
indicates that an underlying command the code tries to use is not implemented. For an example, see the description of the FTPHost.chmod method.
is raised for FTP return codes from the 4xx category. This corresponds to
ftplib.error_tempare not identical).
denotes an I/O error on the remote host. This appears mainly with file-like objects that are retrieved by calling
>>> try: ... f = open("not_there") ... except IOError as obj: ... print(obj.errno) ... print(obj.strerror) ... 2 No such file or directory
>>> 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.
subsumes exception classes for signaling errors due to limitations of the FTP protocol or the concrete implementation of
This exception is raised if the directory in which “you” are placed upon login is not accessible, i.e. a
chdircall with the directory as argument would fail.
is raised if an FTP session instance doesn’t have an
encodingattribute (see also session factories).
is used for errors during the parsing of directory listings from the server. This exception is used by the
Because of the implementation of the
lstatmethod it is not possible to do a
statcall 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.
is used to denote errors which relate to setting the time shift.
FTPHost instances can be created 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. Usually the
session_factory arguments aren’t needed though.
FTPHost objects can also be used in a
import ftputil with ftputil.FTPHost(server, user, password) as ftp_host: print(ftp_host.listdir(ftp_host.curdir))
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
with statement, the instance is closed as well. Exceptions will
be propagated (as with
try ... finally).
The keyword argument
session_factory may be used to generate FTP
connections with other factories than the default
example, the standard library of Python 3 contains a class
ftplib.FTP_TLS which extends
ftplib.FTP to use an encrypted
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
This functionality of the constructor also allows to wrap
objects to do something that wouldn’t be possible with the
As an example, assume you want to connect to another than the default
ftplib.FTP only offers this by means of its
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 enter a ticket.
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
session_factory(base_class=ftplib.FTP, port=21, use_passive_mode=None, encrypt_data_channel=True, encoding=None, debug_level=None)
base_classis a base class to inherit a new session factory class from. By default, this is
ftplib.FTPfrom the Python standard library.
portis the command channel port. The default is 21, used in most FTP server configurations.
use_passive_modeis either a boolean that determines whether passive mode should be used or
Nonemeans to let the base class choose active or passive mode.
encrypt_data_channeldefines whether to encrypt the data channel for secure connections. This is only supported for the base classes
M2Crypto.ftpslib.FTP_TLS, otherwise the parameter is ignored.
encodingcan be a string to set the encoding of directory and file paths on the remote server. (This has nothing to do with the encoding of file contents!) If you pass a string and your base class is neither
ftplib.FTP_TLS, the used heuristic in
session_factorymay not work reliably. Therefore, if in doubt, let
Noneand define your
base_classso that it sets the encoding you want.
Note: In Python 3.9, the default path encoding for
ftplib.FTP_TLSchanged from previously “latin-1” to “utf-8”. Hence, if you don’t pass an
session_factory, you’ll get different path encodings for Python 3.8 and earlier vs. Python 3.9 and later.
If you’re sure that you always use only ASCII characters in your remote paths, you don’t need to worry about the path encoding and don’t need to use the
debug_levelsets 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
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, encoding="UTF-8", 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
connects on command channel 31, will encrypt the data channel, use the
UTF-8 encoding for remote paths 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.
Directory and file names
Keep in mind that this section only applies to directory and file names, not file contents. Encoding and decoding for file contents is handled by the
encodingargument for FTPHost.open.
Generally, paths can be
bytes objects (or
bytes). However, you can’t mix different
string types (
str) in one call (for example in
FTPHost.path.join). If a method gets a string argument (or a string
argument wrapped in a
object) and returns one or more strings, these strings will have the
same string type (
str) as the argument(s). Mixing different
string types in one call (for example in
allowed and will cause a
TypeError. These rules are the same as for
local file system operations.
Although you can pass paths as
bytes, the former is
recommended. See below for the reason.
If you have directory or file names with non-ASCII characters, you
need to be aware of the encoding the session factory
ftplib.FTP) uses. This needs to be the same encoding that the
FTP server uses for the paths.
The following diagram shows string conversions on the way from your code to the remote FTP server. The opposite way works analogously, so encoding steps in the diagram become decoding steps and decoding steps in the diagram become encoding steps.
Both “branching points” in the upper and lower part of diagrams are independent, so depending on how you pass paths to ftputil and which file system API the FTP server uses, there are four possible combinations.
+-----------+ +-----------+ | Your code | | Your code | +-----------+ +-----------+ | | | str | bytes v v +-------------+ +-------------+ decode with encoding of session, | ftputil API | | ftputil API | e.g. `ftplib.FTP` instance +-------------+ +-------------+ \ / \ str / v v +---------------+ encode with encoding | ftplib API | specified in `FTP` instance +---------------+ | | bytes v +-------------+ | socket API | +-------------+ / \ / \ local / client - - - - - / - - - - - \ - - - - - - - - - - - - - - - - - - - - - - / \ remote / server / bytes \ v v +------------+ +------------+ decode with encoding from | FTP server | | FTP server | FTP server configuration +------------+ +------------+ | | | bytes | str v v +-------------+ +-------------+ | remote file | | remote file | | system API | | system API | +-------------+ +-------------+ \ / \ bytes / v v +-------------------+ | file system | +-------------------+
As you can see at the top of the diagram, if you use
(regular unicode strings), there’s one fewer decoding step, and so one
fewer source of problems. If you use
bytes objects for paths, ftputil
tries to get the encoding for the FTP server from the
attribute of the session instance (say, an instance of
encoding attribute is present, a
NoEncodingError is raised.
All encoding/decoding steps must use the same encoding, the encoding the server uses (at the bottom of the diagram). If the server uses the bytes from the socket directly, i.e. without an encoding step, you have to use the file system encoding.
Until and including Python 3.8, the encoding implicitly assumed by the
ftplib module was latin-1, so using
bytes was the safest strategy.
However, Python 3.9 made the
encoding configurable via an
encoding, but defaults to UTF-8.
If you don’t pass a session factory to the
ftputil.FTPHost constructor, ftputil will use latin-1 encoding for the
paths. This is the same value as in earlier ftputil versions in
combination with Python 3.8 and earlier.
- If possible, use only ASCII characters in paths.
- If possible, pass paths to ftputil as
- If you use a custom session factory, the session instances created
by the factory must have an
encodingattribute with the name of the path encoding to use. If your session instances don’t have an
encodingattribute, ftputil raises a
NoEncodingErrorwhen the session is created.
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 does not use the
-a option in the
LIST command to find hidden files.
To tell the server to list hidden directories and files, set
ftp_host = ftputil.FTPHost(server, user, password, account, session_factory=ftplib.FTP) ftp_host.use_list_a_option = True
- If the server doesn’t understand the
-aoption at all, the server may interpret
-aas the name of a file or directory, which can result in odd behavior. Therefore, use
-aonly if you’re sure the server you’re talking to supports it. Another approach is to have test code for
-asupport and fall back to not using the option.
- Even if the server knows about the
-aoption, the server may be configured to ignore it.
FTPHost attributes and methods
are strings which denote the current and the parent directory on the remote server.
sepholds 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.pathto write platform-independent Python code for local filesystems. Keep in mind that most, but not all, arguments of
FTPHostmethods 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
returns the absolute current directory on the remote host. This method works like
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
targetmay 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:
chunkis 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
targetare strings. See the description of
uploadfor more details.
upload_if_newer(source, target, callback=None)
is similar to the
uploadmethod. 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_newerfor 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
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_neweris used a second time. There are at least two possibilities after a failed upload:
- remove the incomplete target file with
FTPHost.remove, then use
upload_if_newerto transfer it again.
download_if_newer(source, target, callback=None)
upload_if_newerbut performs a download from the server to the local host. Read the descriptions of download and
upload_if_newerfor more information. If a download actually happened, the return value is
Time zone correction
download_if_newer to work correctly, the
time zone of the server must be taken into account. By default, ftputil
assumes that the timestamps in server listings are in
sets the so-called time shift value, measured in seconds. The time shift here is defined as the difference between the time used in server listings and UTC.
time_shift = server_time - utc_time
For example, a server in Berlin/Germany set to the local time (currently UTC+03:00), would require a time shift value of 3 * 3600.0 = 10800.0 seconds to be handled correctly by ftputil’s
download_if_newer, as well as the
Note that servers don’t necessarily send their file system listings in their local time zone. Some use UTC, which actually makes sense because UTC doesn’t lead to an ambiguity when there’s a switch back from the daylight saving time to the “normal” time of the server location.
If the time shift value is invalid, for example its absolute value is larger than 24 hours, a
Versions of ftputil before 4.0.0 used a different definition of “time shift”, server_time – local_client_time.
This had the advantage that the default of 0.0 would be correct if the server was set to the same time zone as the client where ftputil runs. On the other hand, this approach meant that the time shift depended on two time zones, not only the one used on the server side. This could be confusing if server and client didn’t use the same time zone.
See also synchronize_times for a way to set the time shift with a simple method call. If you can’t use
synchronize_timesand the server uses the same time zone as the client, you can set the time shift value with
set_time_shift( round( (datetime.datetime.now() - datetime.datetime.utcnow()).seconds, -2 ) )
returns the currently-set time shift value. See
set_time_shiftabove for its definition.
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
If you can’t fulfill these conditions, you can nevertheless set the time shift value explicitly with set_time_shift. Trying to call
synchronize_timesif the above conditions aren’t met results in a
Creating and removing directories
makes the given directory on the remote host. This does not construct “intermediate” directories that don’t already exist. The
modeparameter is ignored; this is for compatibility with
FTPHostobject is passed into a function instead of the
osmodule. See the explanation in the subsection Exception hierarchy.
makedirs(path, [mode], exist_ok=False)
works similar to
mkdir(see above), but also makes intermediate directories like
modeparameter is only there for compatibility with
os.makedirsand is ignored.
exist_okcontrols whether the existence of any directory but the last in the
pathshould be considered an error. If the default
Falseis used or passed to
makedirs, ftputil will raise a
PermanentErrorif any directory but the last already exists.
removes the given remote directory. If it’s not empty, raise a
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
ignore_errorsis set to a true value, errors are ignored. If
ignore_errorsis a false value and
onerrorisn’t set, all exceptions occurring during the tree iteration and processing are raised. These exceptions are all of type
To distinguish between different kinds of errors, pass in a callable for
onerror. This callable must accept three arguments:
funcis a bound method object, for example
pathis the path that was the recent argument of the respective method (
exc_infois the exception info as it is gotten from
The code of
rmtreeis taken from Python’s
shutilmodule and adapted for
Removing files and links
removes a file or link on the remote host, similar to
is an alias for
Retrieving information about directories, files and links
returns a list containing the names of the files and directories in the given path, similar to os.listdir. The special names
..are not in the list.
stat (and some others) rely on the directory
listing format used by the FTP server. When connecting to a host,
FTPHost’s constructor tries to guess the right format, which succeeds
in most cases. However, if you get strange results or
exceptions by a mere
lstat call, please enter a
stat give wrong modification dates or times, look at the
methods that deal with time zone differences (time zone
returns an object similar to that from os.lstat. This is a kind of tuple with additional attributes; see the documentation of the
osmodule for details.
The result is derived by parsing the output of a
LISTcommand on the server. Therefore, the result from
FTPHost.lstatcan not contain more information than the received text. In particular:
User and group ids can only be determined as strings, not as numbers, and that only if the server supplies them. This is usually the case with Unix servers but maybe not for other FTP servers.
Values for the time of the last modification may be rough, depending on the information from the server. For timestamps older than a year, this usually means that the precision of the modification timestamp value is not better than a day. For newer files, the information may be accurate to a minute.
If the time of the last modification is before the epoch (usually 1970-01-01 UTC), set the time of the last modification to 0.0.
Links can only be recognized on servers that provide this information in the
Stat attributes that can’t be determined at all are set to
None. For example, a line of a directory listing may not contain the date/time of a directory’s last modification.
There’s a special problem with stat’ing the root directory. (Stat’ing things in the root directory is fine though.) In this case, a
RootDirErroris raised. This has to do with the algorithm used by
(l)stat, and I know of no approach which mends this problem.
ftputilrecognizes the common Unix-style and Microsoft/DOS-style directory formats. If you need to parse output from another server type, please write to the ftputil mailing list. You may consider writing your own parser.
statinformation also for files which are pointed to by a link. This method follows multiple links until a regular file or directory is found. If an infinite link chain is encountered or the target of the last link in the chain doesn’t exist, a
The limitations of the
lstatmethod also apply to
FTPHost objects contain an attribute named
path, similar to
os.path. The following
methods can be applied to the remote host with the same semantics as for
abspath(path) basename(path) commonprefix(path_list) dirname(path) exists(path) getmtime(path) getsize(path) isabs(path) isdir(path) isfile(path) islink(path) join(path1, path2, ...) normcase(path) normpath(path) split(path) splitdrive(path) splitext(path) walk(path, func, arg)
Like Python’s counterparts under
is... methods return
False if they can’t find the path given by
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
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
object in an
FTPHost’s namespace. For example, after calling
ftp_host = ftputil.FTPHost(host, user, password)
the cache can be accessed as
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
listdir and then process the found directories and
files. This can also happen implicitly by a call to
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
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
getmtime all derive their
results from a previously fetched
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
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
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
FTPHost objects. After some thinking, this turns out to
be very error-prone. For example, it won’t help with different processes
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"))
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
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
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
Iteration over directories
walk(top, topdown=True, onerror=None, followlinks=False)
iterates over a directory tree, similar to os.walk. Actually,
FTPHost.walkuses the code from Python with just the necessary modifications, so see the linked documentation.
path.walk(path, func, arg)
walkmethod in FTPHost.path can be used, though
FTPHost.walkis probably easier to use.
closes the connection to the remote host. After this, no more interaction with the FTP server is possible with this
FTPHostobject. Usually you don’t need to close an
closeif you set up the instance in a
renames the source file (or directory) on the FTP server.
sets the access mode (permission flags) for the given path. The mode is an integer as returned for the mode by the
lstatmethods. 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:
Not all FTP servers support the
chmodcommand. 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 CHMODcommand isn’t allowed.
ftputilmaps this special error response to a
CommandNotImplementedErrorwhich is derived from
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 ...
CommandNotImplementedErroris more specific, you have to test for it first.
copyfileobj(source, target, length=64*1024)
copies the contents from the file-like object
sourceto the file-like object
target. The only difference to
shutil.copyfileobjis 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
targethave to match; the string type read from
sourcemust be an accepted string type when written to
target. For example, if you open
sourcein Python 3 as a local text file and
targetas a remote file object in binary mode, the transfer will fail since
source.readgives unicode strings (
target.writeonly accepts byte strings (
See File-like objects for the construction and use of remote file-like objects.
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
ftputildon’t work for you.
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
FTPHostobject 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_alivefrom a callback function.
keep_alivemethod won’t help if the connection has already timed out. In this case, a
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_alivemethod 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_aliveto 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 range(15): time.sleep(60) ftp_host.keep_alive() # Will raise an `ftputil.error.TemporaryError`. data += fobj.read()
FTPFile objects are returned by a call to
FTPHost.open; never use
FTPFile constructor directly.
The APIs for remote file-like objects is modeled after the APIs of the
open function and its return value.
FTPHost.open(path, mode="r", buffering=None, encoding=None, errors=None, newline=None, rest=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
getcwdmethod). 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
bytesobjects. That is, read operations return
bytesand write operations only accept
Similarly, text files always work with strings (
str). Here, read operations return string and write operations only accept strings.
newlinehave the same semantics as in open.
If the file is opened in binary mode, you may pass 0 or a positive integer for the
restargument. The argument is passed to the underlying FTP session instance (for example an instance of
ftplib.FTP) to start reading or writing at the given byte offset. For example, if a remote file contains the letters “abcdef” in ASCII encoding,
rest=3will start reading at “d”.
If you pass
restvalues which point after the file, the behavior is undefined and may even differ from one FTP server to another. Therefore, use the
restargument only for error recovery in case of interrupted transfers. You need to keep track of the transferred data so that you can provide a valid
restargument for a resumed transfer.
FTPHost.open can also be used in a
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
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
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 >>>
ftp is a single FTP connection, represented by an
ftplib.FTP instance, not an
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 noticeable 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_alivemethod since it calls
pwdon 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_alivedoesn’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
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().ignores_line(line) my_test = ... return is_total_line or my_test
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
|4||st_uid||int||str||usually only available as string|
|5||st_gid||int||str||usually only available as string|
|-||_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
Parser classes can use several helper methods which are defined in the
parse_unix_modeparses strings like “drwxr-xr-x” and returns an appropriate
parse_unix_timereturns a float number usable for the
st_...timevalues 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_timeparses 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
MSParser in the module
To actually use the parser, call the method set_parser
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.
Bugs and limitations
ftputilneeds at least Python 3.6 to work.
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
lstatit 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
- In multithreaded programs, you can have each thread use one or more
FTPHostinstances 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
lstatresults for each
FTPHostobject, i.e. there’s no sharing of cache results determined by several
FTPHostobjects. See Local caching of file system information for the reasons.
If not overwritten via installation options, the
ftputil files reside
ftputil package. There’s also documentation in
reStructuredText and in
HTML format. The locations of these files after installation is
scripted_session.py are for unit-testing. If
you only use
ftputil, i.e. don’t modify it, you can delete these
- Postel J, Reynolds J. 1985. RFC 959 - File Transfer Protocol (FTP).
- Python Software Foundation. 2020. The Python Standard Library.
ftputil is written by Stefan Schwarzer <<email@example.com>>
and contributors (see
lrucache module was written by Evan Prodromou
Feedback is appreciated. :-)