In Python's `ftplib` module, when you call the `ftp.login()` method to establish an FTP connection and log in to an FTP server, error handling depends on whether the login is successful or not. Here's how `ftp.login()` processes errors:
1. **Successful Login**:
If the login is successful, `ftp.login()` returns a success message. You can then proceed to perform FTP operations on the server, such as uploading, downloading, or listing files.
2. **Failed Login**:
If the login attempt fails, `ftp.login()` will raise an exception. The exception can be of type `ftplib.error_perm` if the login credentials are incorrect or `ftplib.error_temp` if the login failed due to a temporary issue, such as a network problem or the server being unavailable.
To handle these exceptions, you should use a `try...except` block. For example:
```python
from ftplib import FTP
try:
ftp = FTP('ftp.example.com')
ftp.login(user='username', passwd='password')
# Proceed with FTP operations after successful login
except ftplib.error_perm as e:
print(f"Login failed: {e}")
except ftplib.error_temp as e:
print(f"Temporary error during login: {e}")
except Exception as e:
print(f"An unexpected error occurred: {e}")
```
In the code above, we use specific `except` blocks for `ftplib.error_perm` and `ftplib.error_temp` to handle login-related errors separately. You can also use a more general `Exception` block to handle unexpected errors that may occur during the login process.
The specific exceptions that can be raised by `ftp.login()` can be found in the `ftplib` module documentation. It's important to handle these exceptions gracefully in your code to provide appropriate error messages or take corrective actions when FTP login fails.