In this tutorial, we’re going to show you how to use Python’s built-in FTP object to transfer files over the internet using the ancient protocol known as FTP (File Transfer Protocol). If you’ve ever struggled with downloading or uploading large files using FTP, then this guide is for you!
First things first: what an FTP object actually is. In Python land, it’s a fancy wrapper around some basic functions that allow us to connect to an FTP server and transfer files back and forth. It’s like having a personal assistant who knows all the ins and outs of this ancient protocol so we don’t have to worry about any of the ***** details ourselves!
Now, let’s take a look at some of these fancy functions that our FTP object provides us with. First up is `connect()`, which allows us to connect to an FTP server using its hostname and login credentials (username and password). Here’s what it looks like in action:
# Import the FTP module from the ftplib library
from ftplib import FTP
# Create an FTP object and assign it to the variable 'ftp'
ftp = FTP('example.com')
# Use the 'login' function of the FTP object to connect to the FTP server
# Provide the hostname, username, and password as parameters
ftp.login('my_username', 'my_password')
# The script now connects to the FTP server and allows us to perform operations on it.
Pretty straightforward, right? Now that we’re connected to the server, let’s take a look at some of the other methods our FTP object provides us with. One of the most useful is `retrbinary()`, which allows us to download files from the server using binary mode (which is important for large files). Here’s what it looks like:
# This script uses the FTP object's `retrbinary()` method to download a file from the server in binary mode and save it locally.
# First, we specify the file we want to retrieve from the server, in this case "my_file.txt", using the `RETR` command.
# Then, we use the `open()` function to create a local file named "my_local_file.txt" and specify that we want to write to it in binary mode using the 'wb' argument.
# Finally, we use the `write` method to write the retrieved file to our local file.
ftp.retrbinary('RETR my_file.txt', open('my_local_file.txt', 'wb').write)
This command tells our FTP object to download the file `my_file.txt` from the server and save it locally as `my_local_file.txt`. The second argument is a callback function that allows us to write the data directly into a local file using binary mode (which is important for large files).
Another useful method is `storbinary()`, which allows us to upload files to the server using binary mode:
# The following script uses the FTP library to upload a local file to a server using binary mode.
# Import the FTP library
import ftplib
# Connect to the server using FTP
ftp = ftplib.FTP('server_address')
# Open the local file in read binary mode
with open('my_local_file.txt', 'rb') as f:
# Use the storbinary() method to upload the file to the server
# The first argument is the command to store the file on the server
# The second argument is the local file object
ftp.storbinary('STOR my_new_file.txt', f)
# Close the FTP connection
ftp.close()
This command tells our FTP object to upload the file `my_local_file.txt` from our local machine and save it on the server under the name `my_new_file.txt`. The second argument is a callback function that allows us to read data directly from a local file using binary mode (which is important for large files).
Now, some of the less commonly used methods our FTP object provides us with. One such method is `dir()`, which allows us to list all the files and directories in the current directory:
# This script uses the FTP object's `retrlines()` method to list all the files and directories in the current directory.
# Import the necessary module for FTP operations
import ftplib
# Create an FTP object and connect to the FTP server
ftp = ftplib.FTP('ftp.server.com')
# Login to the FTP server with username and password
ftp.login('username', 'password')
# Set the transfer mode to binary
ftp.set_pasv(True)
# Use the `retrlines()` method to list all the files and directories in the current directory
ftp.retrlines('LIST')
# Close the FTP connection
ftp.quit()
This command tells our FTP object to send a LIST request to the server, which will return a list of all the files and directories in the current directory (along with some other information that we don’t really care about). The output is printed directly to the console.
Another useful method is `cwd()`, which allows us to change the working directory on the server:
# This script uses the FTP module to connect to a server and perform various operations.
# Import the FTP module
import ftplib
# Connect to the server using the FTP class and store the connection in a variable
ftp = ftplib.FTP('server_address')
# Log in to the server using the login method and provide the username and password
ftp.login('username', 'password')
# Use the listdir method to get a list of all files and directories in the current directory
# The output is printed directly to the console
file_list = ftp.listdir()
# Use the cwd method to change the working directory on the server
# This allows us to navigate to a specific directory on the server
ftp.cwd('my_directory')
# Close the connection to the server using the quit method
ftp.quit()
This command tells our FTP object to change the current working directory on the server to `my_directory`. If this directory doesn’t exist, an error will be raised.
Finally, some of the less commonly used methods that are still worth mentioning. One such method is `quit()`, which allows us to disconnect from the FTP server:
# This script uses the FTP module to connect to a server and change the current working directory to 'my_directory'.
# Import the FTP module
import ftplib
# Create an FTP object and connect to the server
ftp = ftplib.FTP('server_address')
# Login to the server with a username and password
ftp.login('username', 'password')
# Change the current working directory to 'my_directory'
ftp.cwd('my_directory')
# Check if the directory exists
if 'my_directory' in ftp.nlst():
# If it exists, print a success message
print("Directory changed successfully!")
else:
# If it doesn't exist, raise an error
raise ftplib.error_perm("Directory does not exist on the server.")
# Disconnect from the FTP server
ftp.quit()
# The quit() method allows us to disconnect from the FTP server.
This command tells our FTP object to send a QUIT request to the server, which will cause it to close the connection and exit gracefully.
Another useful method is `voidcmd(command)`, which allows us to execute arbitrary commands on the server:
# This command uses the FTP object to send a QUIT request to the server, closing the connection and exiting gracefully.
ftp.quit()
# This method allows us to execute arbitrary commands on the server. Here, we use it to change the permissions of a directory to 755.
ftp.voidcmd('SITE CHMOD 755 my_directory')
This command tells our FTP object to send a SITE CHMOD request to the server, which will change the permissions of `my_directory` to 755 (which is important for large files). The output is not printed directly to the console.
And that’s it! We’ve covered all the basics you need to know about FTP objects in Python. With these tools at your disposal, you can now transfer files over the internet like a pro. Just remember to always use binary mode for large files and be careful with permissions (especially if you’re working on someone else’s server).
Now let’s take a look at how we can implement property() in Python using an example from the context provided:
# This script is creating a class called Property that emulates the PyProperty_Type() function in Python.
class Property(object):
# This is the constructor method for the Property class, which takes in four parameters: fget, fset, fdel, and doc.
def __init__(self, fget=None, fset=None, fdel=None, doc=None):
# The fget parameter represents the function used to get the property value.
self.fget = fget
# The fset parameter represents the function used to set the property value.
self.fset = fset
# The fdel parameter represents the function used to delete the property value.
self.fdel = fdel
# The doc parameter represents the documentation for the property.
self.__doc__ = doc
# This method is used to get the property value.
def __get__(self, instance, owner):
# If the instance is None, return the Property class itself.
if instance is None:
return self
# Otherwise, use the fget function to get the property value and return it.
else:
value = self.fget(instance)
return value
# This method is used to set the property value.
def __set__(self, instance, value):
# Check if the fset function has a __func__ attribute, which indicates it is a bound method.
if hasattr(self.fset, '__func__'):
# If it is a bound method, call it with the instance and value parameters.
self.fset(instance, value)
# This method is used to delete the property value.
def __del__(self, instance):
# Check if the fdel function has a __func__ attribute, which indicates it is a bound method.
if hasattr(self.fdel, '__func__'):
# If it is a bound method, call it with the instance parameter.
self.fdel(instance)
In this example, we’re creating a property called Property that emulates the behavior of PyProperty_Type() in Objects/descrobject.c. This is useful for implementing custom properties with getters and setters using Python’s descriptor protocol.