ftplib raises an error if the status code of the response starts with a '5'. That means the server is returning a 5xx error:
0.5.1 500 Internal Server Error
The server encountered an unexpected condition which prevented it from
fulfilling the request.
10.5.2 501 Not Implemented
The server does not support the functionality required to fulfill the
request. This is the appropriate response when the server does not
recognize the request method and is not capable of supporting it for
any resource.
10.5.3 502 Bad Gateway
The server, while acting as a gateway or proxy, received an invalid
response from the upstream server it accessed in attempting to fulfill
the request.
10.5.4 503 Service Unavailable
The server is currently unable to handle the request due to a
temporary overloading or maintenance of the server. The implication is
that this is a temporary condition which will be alleviated after some
delay. If known, the length of the delay MAY be indicated in a
Retry-After header. If no Retry-After is given, the client SHOULD
handle the response as it would for a 500 response.
Note: The existence of the 503 status code does not imply that a
server must use it when becoming overloaded. Some servers may wish
to simply refuse the connection.
10.5.5 504 Gateway Timeout
The server, while acting as a gateway or proxy, did not receive a
timely response from the upstream server specified by the URI (e.g.
HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
to access in attempting to complete the request.
Note: Note to implementors: some deployed proxies are known to
return 400 or 500 when DNS lookups time out.
10.5.6 505 HTTP Version Not Supported
The server does not support, or refuses to support, the HTTP protocol
version that was used in the request message. The server is indicating
that it is unable or unwilling to complete the request using the same
major version as the client, as described in section 3.1, other than
with this error message. The response SHOULD contain an entity
describing why that version is not supported and what other protocols
are supported by that server.
According to the ftp docs:
FTP.retrbinary(command, callback[, maxblocksize[, rest]])
Retrieve a
file in binary transfer mode. command should be an appropriate RETR
command: 'RETR filename'.
But you wrote this:
ftp.retrbinary('RETR' + filename, localfile.write, 1024)
which will produce something like this:
ftp.retrbinary('RETRdog.jpg', localfile.write, 1024)
You need to add a space after 'RETR'.
Create your own ftp server with python
By the way, you can write a short python program that will act as an ftp server. First install the module pyftpdlib:
$ pip3.4 install pyftpdlib #See note on 3.4 below
If you only have one version of python on your system, you can just write:
$ pip install pyftpdlib
If you have more than one version of python on your computer, substitute the correct version number for 3.4. The version number you specify is the python version where the pyftpdlib module will install.
Here is what an ftp server looks like in python:
from pyftpdlib.authorizers import DummyAuthorizer
from pyftpdlib.handlers import FTPHandler
from pyftpdlib.servers import FTPServer
my_authorizer = DummyAuthorizer()
my_authorizer.add_user(
username = '7stud',
password = '1234',
homedir = '.',
perm='elrw' #permissions: 'e'->change dir, 'l'->list files, 'r'->retrieve files, 'w'->store a file to the server
)
my_handler = FTPHandler
my_handler.authorizer = my_authorizer
port = 2121
my_handler.banner = "You connected to my ftp server on port: {}".format(port)
address = ('localhost', port)
server = FTPServer(address, my_handler)
server.max_cons = 256
server.max_cons_per_ip = 5
server.serve_forever()
pyftpdlib docs and tutorial here.
add_user() and permissions described here.
Then, you can create a directory for your server:
$ mkdir ftp_server
$ cd ftp_server
$ touch my_ftp_server.py
Put the code above into the file my_ftp_server.py. Then add some files to the ftp_server directory that you want to practice 'downloading'. Then start up the server by running my_ftp_server.py.
In another terminal window, switch directories to the directory containing your python program:
$ cd python_programs
Then make some minor changes to your ftp client program:
from ftplib import FTP
def getfile(conn): #It's good practice not to refer to global variables in your functions.
#Instead, pass in any values your function needs as arguments.
conn.retrlines('LIST') # List directory contents
filename = input('Name of file: ')
localfile = open(filename, 'wb')
ftp_command = 'RETR {}'.format(filename)
conn.retrbinary(ftp_command, localfile.write, 1024)
localfile.close()
user = '7stud'
passw = '1234'
port = 2121
url = input('FTP url: ').lower().strip()
ftp = FTP()
ftp.connect(url, port)
ftp.login(user, passw)
getfile(ftp)
ftp.quit()
Here's a sample run of your ftp client program:
~/python_programs$ python3.4 ftp_client.py
FTP url: localhost
drwxr-xr-x 4 7stud staff 136 Feb 11 09:07 cgi-bin
-rw-r--r-- 1 7stud staff 3446 Jun 08 2013 client_socket.py
-rw-r--r-- 1 7stud staff 680 Feb 15 03:03 ftp_server.py
-rw-r--r-- 1 7stud staff 721 Feb 12 03:01 http_server.py
-rw-r--r-- 1 7stud staff 498 Jan 01 07:10 index.html
-rw-r--r-- 1 7stud staff 68 Jan 01 05:03 oneliner.py
-rw-r--r-- 1 7stud staff 954 Feb 11 09:05 socket_server.py
-rw-r--r-- 1 7stud staff 0 Feb 15 02:50 test.png
Name of file: test.png
~/python_programs$ ls *.png
bar_freq.png example.png test.png
~/python_programs$
