SoFunction
Updated on 2025-05-15

Implementation Guide for Writing FTP Automated Upload Download Scripts in Python

introduction

Python provides a simple and powerful way to write FTP automation scripts, using the ftplib library to implement file upload and download functions. This script includes methods to connect to an FTP server, upload files, download files, and automate these tasks. With real-life cases and code examples, this guide shows how to get started quickly, automate file transfers, and how to scale according to requirements, such as adding error handling, logging, and multithreading support.

1. Introduction to ftplib library

1.1 Introduction to FTP protocol

FTP (File Transfer Protocol) is a protocol used to transfer files on the network. It allows users to upload files from one computer to another and download files from another computer. FTP uses two ports: 21 for command transmission and 20 for data transmission. It works through a client-server model where users interact with the FTP server through FTP client software.

1.2 The role of ftplib library

ftplib is a built-in standard library for Python that encapsulates many details of the FTP protocol, allowing users to perform FTP operations through simple interfaces. Using ftplib, developers can realize file upload and download, directory browsing, and other FTP server interaction functions without having to understand the complexity of the FTP protocol in depth.

1.3 The main functional modules of ftplib

The ftplib library mainly consists of several classes, the most important of which include the FTP class, which is used to create connections to the FTP server and log in; the FTPS class, which provides support for encrypted connections (using SSL/TLS); and exception handling classes such as error_reply. These classes and methods form the core of ftplib, allowing Python programmers to easily implement FTP client functions.

Through the study of this chapter, we will lay the foundation for the operation of the ftplib library and lay a solid foundation for further in-depth discussions on how to use this library for efficient file transfer. In the next chapter, we will dive into how to use ftplib for FTP connection and login.

2. FTP connection and login

Connect to the FTP server

To use the ftplib library to connect to the FTP server, you need to import the library first and create an FTP object, and then use theconnect Method specifies the address and port number of the FTP server (default is 21). The code example is as follows:

import ftplib
 
ftp = ()  # Create an FTP object('')  # Connect toFTPserver

Connection parameter analysis

  • FTP() : Create an instance of the FTP object representing the connection to the FTP server.
  • connect() : Used to establish a connection to the FTP server.
  • Parameter 1 (host ): The host name or IP address of the FTP server.
  • Parameter 2 (port ): The port that the FTP server listens to, the default is 21.

After the connection is successful, you can useprint(()) To check if the connection is successful and print out the welcome message.

Network exception handling

In practical applications, network problems may cause connection failure. To this end, it is necessary to handle exceptions on the connection process to ensure the robustness of the program. The code example is as follows:

try:
    ('', port=21)
except ftplib.error_perm as e:
    print('Connection failed:', e)

Used heretry-except Statement captureftplib Possible exceptions to be thrown, thus handling network connection exceptions.

User login

After the connection is successful, the next step is usually to log in to the FTP server. You can use FTP objectslogin Method to log in to the user, and you need to provide a user name and password. The code example is as follows:

('username', 'password')  # User login

Login parameter analysis

  • login() : Used to log in to the FTP server.
  • Parameter 1 (user ): username.
  • Parameter 2 (passwd ): password.

Similarly, exceptions may occur during the login process (such as username or password error), so exception handling is required:

try:
    ('username', 'password')
except ftplib.error_perm as e:
    print('Login failed:', e)

Solution to failure of permission verification

If the login fails, it is usually due to permission verification issues. First, confirm whether the provided username and password are correct, then check whether the FTP server is configured correctly and whether anonymous login is allowed (if anonymous account is used). If the problem remains the same, you may need to contact the server administrator for further troubleshooting.

Deep in code level

Use the ftplib interface to achieve effective communication

The ftplib library provides rich interfaces for interacting with an FTP server. Here are some commonly used interfaces and their uses:

  • nlst() : List the directory contents on the FTP server.
  • cwd() : Change the current working directory.
  • size() : Gets the size of the specified file.
  • delete() : Delete the specified file.

These interfaces are called via FTP objects, e.g.() The file list in the current directory will be listed.

Example of effective communication code to implement FTP server

The following is a code example that implements effective communication with an FTP server through the ftplib interface:

# List the file list in the current directorytry:
    files = ()
    for f in files:
        print(f)
except ftplib.error_perm as e:
    print('Failed to list files:', e)
 
# Change the working directorytry:
    ('target_directory')
except ftplib.error_perm as e:
    print('Change working directory failed:', e)
 
# Get file sizetry:
    file_size = ('')
    print(f'The file size is {file_size} byte')
except ftplib.error_perm as e:
    print('Failed to get file size:', e)
 
# Delete the filetry:
    ('file_to_delete.txt')
except ftplib.error_perm as e:
    print('Delete file failed:', e)

Among these operations, exception handling is indispensable. It can help us better understand the cause of the error and make corresponding handling.

In the next section, we will explore how to implement file upload function through the ftplib library and penetrate into more complex application scenarios.

3. File upload function implementation

Introduction to key functions for file upload

The FTP protocol supports file upload operations, and there are two main upload methods:storbinary andstorlines 。 storbinary Used for uploading binary files, andstorlines Suitable for uploading text files. In the ftplib library, both methods are encapsulated, allowing developers to implement file upload operations more easily.

storbinary function

storbinary The function accepts a command string and an iterable file object, which gradually reads data blocks from the file object and uploads them. usestorbinary When providing a formatted command string, usually"STOR filename" ,infilename It is the corresponding file name on the server.

storlines function

storlines Functions are suitable for uploading text files, and their usage methods are as followsstorbinary Similar, but it does not process binary data in the file object, but uploads the text line directly to the server.

The following chapters will demonstrate how to use these two functions in real-life applications through sample code.

Example code display

Upload files using storbinary

from ftplib import FTP
 
def upload_file_binary(ftp, local_path, remote_path):
    with open(local_path, 'rb') as fp:
        (f'STOR {remote_path}', fp)

In the above example, the upload_file_binary function receives the FTP connection object ftp , the local file path local_path and the file path remote_path on the remote server as parameters. The function opens the local file in binary mode through the with statement and calls the storbinary method to upload the file.

Upload text files using storlines

def upload_file_text(ftp, local_path, remote_path):
    with open(local_path, 'r') as fp:
        (f'STOR {remote_path}', fp)

This function andupload_file_binary Similar, but it opens the local file in text mode and usesstorlines Method to upload. This upload method is suitable for uploading plain text files.

Common error handling of file upload

No error exists in the file

If the file is not properly checked before attempting to upload it, it will causeFileNotFoundError abnormal. To avoid this, you should add code to check the existence of the file before uploading:

import os
 
def check_file_exists(file_path):
    if not (file_path):
        raise FileNotFoundError(f"The file {file_path} does not exist.")

Upload interrupt error

During the upload process, you may encounter network fluctuations and cause upload interruption. This problem can be handled by catching exceptions and retry mechanisms:

def try_upload(max_attempts=3):
    attempts = 0
    while attempts < max_attempts:
        try:
            upload_file_binary(ftp, local_path, remote_path)
            break
        except Exception as e:
            attempts += 1
            print(f"Upload failed: {e}. Retrying ({attempts}/{max_attempts})")
    if attempts == max_attempts:
        print("Max attempts reached. Upload failed.")

This code will try the mostmax_attempts Upload the file once, if an exception occurs in each attempt, an error message is printed and retryed until success or maximum attempts are reached.

Complete file upload function implementation

class FTPUploader:
    def __init__(self, ftp):
         = ftp
 
    def upload(self, local_path, remote_path):
        try:
            self.check_file_exists(local_path)
            with open(local_path, 'rb') as fp:
                (f'STOR {remote_path}', fp)
        except Exception as e:
            print(f"Error occurred: {e}")
 
    def check_file_exists(self, file_path):
        if not (file_path):
            raise FileNotFoundError(f"The file {file_path} does not exist.")

The above is a complete FTPUploader class, which contains methods to verify whether the file exists and upload the file. After this class is instantiated, you only need to provide an FTP connection instance and then call the upload method to perform the file upload operation.

Error handling and logging

In the process of implementing the file upload function, appropriate error handling and logging should be added to facilitate tracking of exceptions and status information during the upload process. In Python, the logging function can be implemented through the built-in logging module.

Setting up logging

import logging
 
def setup_logging():
    (level=,
                        format='%(asctime)s - %(levelname)s - %(message)s',
                        datefmt='%Y-%m-%d %H:%M:%S')

This code will configure the logger, use the INFO level and provide the format of timestamps, log levels, and messages. This allows log information to be recorded in the console or in the file.

Use logging in upload function

def upload(self, local_path, remote_path):
    self.check_file_exists(local_path)
    try:
        with open(local_path, 'rb') as fp:
            (f'STOR {remote_path}', fp)
        (f"File {local_path} uploaded to {remote_path}")
    except Exception as e:
        (f"Upload failed: {e}")

When uploading a file, if the upload is successful, an INFO-level log will be recorded; if an exception occurs, an ERROR-level log will be recorded. This allows real-time monitoring of status and recording any problems that occur during file upload.

Through the above chapters, we not only learned how to use the ftplib library to implement the file upload function, but also learned about possible errors and how to effectively handle them during the upload process. At the same time, we introduced how to integrate logging and error handling into file upload operations. These knowledge points can help developers write robust and reliable file upload scripts.

4. File download function implementation

File transfer is an important part of network communication, and FTP, as one of the important protocols for file transfer, has many conveniences and efficiency when downloading files. In this chapter, we will introduce in detail the steps of using Python's ftplib library to implement file downloads, including explanations of core functions related to downloads, specific code examples, and error handling and download speed optimization strategies.

Key functions and methods

To implement file download function, you must first be familiar with the download-related functions in the ftplib library.retrbinary Method is used to download files in binary mode, andretrlines The method is downloaded in text mode. and Functions like this can list files on the FTP server.

Retrbinary function

retrbinary The usage format of the function is as follows:

def retrbinary(self, cmd, callback, blocksize=8192, rest=None):
  • cmd : Commands sent to the server to request files, e.g.RETR filename 。
  • callback : Data block callback function, usually usedStringIO orBytesIO Object to save downloaded data.
  • blocksize : The size of the data block.
  • rest : Where to start downloading in the file, it is often used for breakpoint continuous transmission.

Retrlines function

retrlines The function usage format is as follows:

def retrlines(self, cmd, callback):
  • cmd : sameretrbinary 。
  • callback : Callback function when the server sends a line of data.

Sample code

Below is a simple code example showing how to use itretrbinary Function downloads a text file:

from ftplib import FTP
from io import BytesIO
 
def download_file(ftp, remote_file_path, local_file_path):
    local_file = open(local_file_path, 'wb')
    try:
        ('RETR ' + remote_file_path, local_file.write)
    except Exception as e:
        print('An error occurred during downloading:', e)
    finally:
        local_file.close()
 
# Assume that the FTP server has been successfully connected and logged inftp = FTP('')
(user='username', passwd='password')
 
# Download the file named on the FTP serverdownload_file(ftp, '', '')
 
()

In the above code, we definedownload_file Function, which accepts FTP objects, remote file paths, and local file paths as parameters. passretrbinary Method, download the file in binary mode and save it to the local path. At the same time, we demonstrate the logic of error handling to ensure that the open file is closed and the error message is printed when an exception occurs.

File download implementation

To realize a complete file download function, it is necessary to consider the file acquisition method, saving location, display of download progress, and processing of the file after downloading. When implementing the download function, you should first check whether the local file exists. If it exists and is the same size as the file on the remote server, you can skip the download process.

Download progress display

In order to improve the user experience, we can display the download progress. For example, in the abovedownload_file In the function, you can passBytesIO The object records the amount of data written to calculate the download progress:

from io import BytesIO
 
def download_file(ftp, remote_file_path, local_file_path):
    local_file = open(local_file_path, 'wb')
    total_size = int((remote_file_path))  # Get the remote file size    progress = BytesIO()
    try:
        ('RETR ' + remote_file_path, )
        (0)
        downloaded = len(())  # The amount of data downloaded        print(f"Download progress: {downloaded}/{total_size} ({downloaded / total_size * 100:.2f}%)")
    except Exception as e:
        print('An error occurred during downloading:', e)
    finally:
        local_file.close()

Breakpoint continuous transmission

Breakpoint continuous transmission means that after the network download is interrupted, you can restart the download from the last interrupted place, rather than re-downloading the entire file. This can greatly improve download efficiency, especially when downloading large files. passretrbinary Functionalrest Parameters can realize breakpoint continuous transmission:

def download_file_resumable(ftp, remote_file_path, local_file_path):
    local_file = open(local_file_path, 'ab')  # Open the file in append mode    progress = BytesIO()
    try:
        # Try to get the local file size, if it does not exist, it is 0        local_file.seek(0, 2)  # Move to the end of the file        local_file_size = local_file.tell()
        # Get file size from the server        remote_file_size = int((remote_file_path))
        # Calculate the file size to be downloaded        size = remote_file_size - local_file_size
        # If the local file size is smaller than the server file size, download it from the rest        if local_file_size &lt; remote_file_size:
            ('RETR ' + remote_file_path, , rest=local_file_size)
            local_file.write(())
            downloaded = local_file_size + len(())
            print(f"Download progress: {downloaded}/{remote_file_size} ({downloaded / remote_file_size * 100:.2f}%)")
        else:
            print("The local file has been downloaded in full.")
    except Exception as e:
        print('An error occurred during downloading:', e)
    finally:
        local_file.close()

Download speed optimization and file integrity verification

Download speed is an important part of the user experience, especially for large file downloads. To optimize download speed, you can try to increase the size of the data block (blocksize parameter). However, it is necessary to set it reasonably according to network conditions to avoid excessive server pressure or network congestion.

Download speed optimization

Increasing the block size can increase speed by reducing the number of interactions with the FTP server. However, excessively large data blocks can cause buffer overflow or network latency issues. Therefore, when optimizing download speed, multiple attempts are required to find the optimal data block size.

def download_file_optimized(ftp, remote_file_path, local_file_path):
    local_file = open(local_file_path, 'wb')
    try:
        ('RETR ' + remote_file_path, local_file.write, blocksize=16384)  # Set larger block size    except Exception as e:
        print('An error occurred during downloading:', e)
    finally:
        local_file.close()

File integrity verification

In order to ensure that the downloaded file is complete and not tampered with, we need to verify the integrity of the downloaded file. Usually, hash algorithms such as MD5 or SHA1 are used to verify files.

import hashlib
 
def verify_file_integrity(local_file_path, expected_md5):
    hash_md5 = hashlib.md5()
    with open(local_file_path, 'rb') as file:
        for chunk in iter(lambda: (4096), b""):
            hash_md5.update(chunk)
    return hash_md5.hexdigest() == expected_md5
 
#User Exampleexpected_md5 = 'your_expected_md5_value'  # Need to obtain in advanceif verify_file_integrity('', expected_md5):
    print("File integrity verification was successful.")
else:
    print("File integrity verification failed.")

summary

In this chapter, we have learned in-depth knowledge points about using the ftplib library to implement file download function. We first introduce the key download functions and methods, and then show how to write a reliable file download function through specific code examples. On this basis, we discussed the importance and implementation methods of download progress display, breakpoint continuous transmission, speed optimization, and file integrity verification.

Through the above content, readers should be able to master how to use Python to perform efficient, stable and secure file download operations. In the following chapters, we will learn more about how to integrate file upload and download capabilities into automated scripts and implement complex automated file transfer tasks.

5. Automatic file transfer script writing

5.1 Ideas for designing automated scripts

When designing automated file transfer scripts, the first thing to do is to clarify the main tasks and target environment of the script. This includes determining the type of file that needs to be uploaded and downloaded, as well as relevant information about the FTP server, such as address, port, username, password, etc. Then plan the script execution process, including initializing connections, file operations (uploading, downloading), disconnecting, etc., and add necessary exception handling mechanisms to the script to improve its robustness.

5.2 Implementation steps and code examples

Step 1: Connect to the FTP server

Use the FTP class of the ftplib library to establish a connection to the server. If the connection is successful, log in to the server; if the failure occurs, an exception is thrown and exception handling is performed.

import ftplib
 
def connect_ftp(server, username, password):
    ftp = (server)
    try:
        (username, password)
        print("Successfully connected and logged into the FTP server.")
    except Exception as e:
        print(f"Connection or login failed：{e}")
    return ftp

Step 2: File upload and download

Write file upload and download functions, and use them separatelystorbinary andretrbinary Method to operate.

def upload_file(ftp, local_file_path, remote_file_path):
    with open(local_file_path, 'rb') as file:
        (f'STOR {remote_file_path}', file)
    print(f"document {local_file_path} Uploaded to {remote_file_path}")
 
def download_file(ftp, remote_file_path, local_file_path):
    with open(local_file_path, 'wb') as file:
        (f'RETR {remote_file_path}', )
    print(f"document {remote_file_path} Downloaded to {local_file_path}")

Step 3: Task Scheduling and Multithreading

To improve efficiency, you can use Python'sthreading Module to implement multi-threaded operation, and use it at the same timeschedule Module to set timing tasks.

import threading
import schedule
 
def schedule_file_transfer():
    # Here you can define the rules and time of the timing task    ().("10:00").do(upload_and_download_files)
 
def upload_and_download_files():
    ftp = connect_ftp('', 'username', 'password')
    if ftp:
        upload_file(ftp, 'path/to/local/file', 'path/to/remote/file')
        download_file(ftp, 'path/to/remote/file', 'path/to/local/file')
        ()  # Close the connection

Step 4: Logging

Record key information during script operation to facilitate subsequent analysis and troubleshooting.

import logging
 
def setup_logging():
    (level=,
                        format='%(asctime)s - %(levelname)s - %(message)s')
    return ()
 
def log_transfer_info(logger, message):
    (f"File transfer information: {message}")
 
# Called in file upload and download functions log_transfer_info To record the log

Step 5: Integration and Testing

Integrate the above steps into a script file and conduct adequate testing to ensure that the script works as expected.

if __name__ == '__main__':
    logger = setup_logging()
    schedule_file_transfer()
    while True:
        schedule.run_pending()
        # Here you can add other tasks or let the program sleep for a while

5.3 Actual case analysis

Demonstrate the specific application scenarios of automated file transfer scripts through a practical case. For example, suppose you need to upload the backup files of the local database to the FTP server regularly every day and download the latest configuration files from the server to the local area.

5.4 Error handling and optimization suggestions

During the testing and use of scripts, pay attention to recording and analyzing possible exceptions and optimize scripts in a timely manner. For example, the strategies for network latency and disconnection can be optimized to improve the stability and reliability of file transfers.

Through the above steps, we can build a basic automated file transfer script. In actual use, it also needs to be adjusted and optimized according to specific needs.

The above is the detailed content of the implementation guide for writing FTP automated upload and download scripts in Python. For more information about Python FTP automated upload and download, please follow my other related articles!