Unlike SFTP, FTP uses the plaintext file transfer method. This means any username or password transferred through the wire can be detected by an unrelated third party. Even though FTP is a very popular file transfer protocol, people frequently use this to transfer a file from their PCs to remote servers.

FTPlib is a Python library that will allow us to connection to an FTP server from a script. To begin, we must have installed Python in our operating system and the FTPLib package. We can install them on a Linux system in two ways:

 pip install ftplib
 apt-get install python-ftplib

In Python, ftplib is a built-in module that's used to transfer files to and from the remote machines. You can create an anonymous FTP client connection with the FTP() class:

ftp_client = ftplib.FTP(path, username, email)

Then, you can invoke the normal FTP commands, such as the CWD command, to list the files in a specific directory. To download a binary file, you need to create a file handler, such as the following:

file_handler = open(DOWNLOAD_FILE_NAME, 'wb')

To retrieve the binary file from the remote host, the syntax shown here can be used, along with the RETR command:

ftp_client.retrbinary('RETR remote_file_name', file_handler.write)

In the following script, we are trying to connect to the FTP server, ftp.free.fr, to get get a list of directories with the dir() method, and download a specific file on that server. To download a file through the ftplib libraries, we will use the retrbinary method. We need to pass two things to it as an input parameter: the retr command with the name of the file and a callback function that will be executed every time a block of data is received. In this case it will write it in a file of the same name.

You can find the following code in the ftp_download_file.py file:

!/usr/bin/env python3

import ftplib

FTP_SERVER_URL = 'ftp.free.fr'
DOWNLOAD_DIR_PATH = '/mirrors/ftp.kernel.org/linux/kernel/Historic/'
DOWNLOAD_FILE_NAME = 'linux-0.01.tar.gz'

def ftp_file_download(path, username):
    # open ftp connection
    ftp_client = ftplib.FTP(path, username)
    print("Welcome:", ftp_client.getwelcome())
    # list the files in the download directory
    ftp_client.cwd(DOWNLOAD_DIR_PATH)
    print("Current working directory:", ftp_client.pwd())
    print("File list at %s:" %path)
    files = ftp_client.dir()
    print(files)
    # download a file
    try:
        file_handler = open(DOWNLOAD_FILE_NAME, 'wb')
        ftp_cmd = 'RETR %s' %DOWNLOAD_FILE_NAME
        ftp_client.retrbinary(ftp_cmd,file_handler.write)
        file_handler.close()
        ftp_client.quit()
    except Exception as exception:
        print('File could not be downloaded:',exception)

if __name__ == '__main__':
    ftp_file_download(path=FTP_SERVER_URL,username='anonymous')

The preceding code illustrates how an anonymous FTP can be downloaded from ftp.free.fr, which hosts the first Linux kernel version. The FTP() class takes three arguments, such as the initial filesystem path on the remote server, the username, and the email address of the ftp user. The FTP.cwd() function is used to change the directory or folder (change the working directory). In this case, after accessing as an anonymous user, change the location to the kernel/Historic folder.

For anonymous downloads, no username and password is required. So, the script can be downloaded from the linux-0.01.tar.gz file, which can be found on the /mirrors/ftp.kernel.org/linux/kernel/Historic/ path.

In the following screenshot, we can see the execution of the previous script:

Another way to get information about the files and folders in the current location is to use the retrlines() method, which can indicate the commands to execute. LIST is a command that's defined by the protocol, as well as others that can also be applied in this function as RETR, NLST, or MLSD.

The second parameter is the callback function, which is called for each piece of received data:

def callback(info):
    print info
 ...
 ftp.retrlines('LIST', callback)

In this example, instead of using the ntransfercmd() method to apply a RETR command, we receive data in a byte array. We execute the RETR command to download the file in binary mode.

You can find the following code in the ftp_download_file_bytes.py file:

#!/usr/bin/env python3

import os, sys
from ftplib import FTP

f = FTP('ftp.free.fr')
f.login()

f.cwd('/mirrors/ftp.kernel.org/linux/kernel/Historic/')
f.voidcmd("TYPE I")

datasock, size = f.ntransfercmd("RETR linux-0.01.tar.gz")
bytes_so_far = 0
fd = open('linux-0.01.tar.gz', 'wb')

while 1:
    buf = datasock.recv(2048)
    if not buf:
        break
    fd.write(buf)
    bytes_so_far += len(buf)
    print("
Received", bytes_so_far, end=' ')
    if size:
        print("of %d total bytes (%.1f%%)" % (
        size, 100 * bytes_so_far / float(size)),end=' ')
    else:
        print("bytes", end=' ')
 sys.stdout.flush()

print()
fd.close()
datasock.close()
f.voidresp()
f.quit()

In this example, we are going to list versions that are available in the Linux kernel ftp with the dir() method.

You can find the following code in the  list_kernel_versions.py file:

#!/usr/bin/env python3

from ftplib import FTP

entries = []
f = FTP('ftp.free.fr')
f.login()
f.cwd('/mirrors/ftp.kernel.org/linux/kernel/')
f.dir(entries.append)
print("%d entries:" % len(entries))
for entry in entries:
    print(entry)
f.quit()

In the following screenshot, we can see the execution of the previous script: