Searching for some kind of data type

[Giampaolo Rodola']

Hi,
for an FTP server I wrote I'd need to group the FTP commands in one
table that defines the command itself, the syntax string, required
permission, whether it requires authorization, whether it takes
argument and whether there's a need to validate the path from the
argument.
The more obvious way I found to do that is something like this:

class CommandProperty:
def __init__(self, perm, auth_needed, arg_needed, check_path,
syntax):
self.perm = perm
self.auth_needed = auth_needed
self.arg_needed = arg_needed
self.check_path = check_path
self.syntax = syntax

ftp_cmds = {
"ABOR" : CommandProperty(perm=None, auth_needed=True,
arg_needed=False, check_path=False, syntax="ABOR (abort transfer)."),
"APPE" : CommandProperty(perm='a', auth_needed=True,
arg_needed=True, check_path=True, syntax="APPE <SP> file-name
(append data to an existent file)."),
"CDUP" : CommandProperty(perm='e',
auth_needed=True,arg_needed=False, check_path=False, syntax="CDUP (go
to parentdirectory)."),
...
...
...
}

....but I find it somewhat redundant and... "ugly".
I was wondering if there was some kind of data type which could better
fit such purpose or if someone could suggest me some other approach to
do this same thing. Maybe using a dictionary is not the better choice
here.


Thanks in advance


--- Giampaolo
http://code.google.com/p/pyftpdlib/

 

[Gary Herron]

Seems completely reasonable to me. You might just consider using
keyword arguments in the __init__ method and eliminate the dictionary
altogether.

Not tested, but you will get the idea:

class CommandProperty:
def __init__(self, perm = perm, auth_needed = True, arg_needed =
True,
check_path = False, syntax = syntax):

self.perm = perm
self.auth_needed = auth_needed
self.arg_needed = arg_needed
self.check_path = check_path
self.syntax = syntax

ftpCommands = dict(
ABOR = CommandProperty(perm = None, arg_needed = False,
syntax="ABOR (abort transfer)."),
APPE = CommandProperty(perm = 'a', check_path=True,
syntax = "APPE <SP> file-name (append data to" \
"an existent file)."),
CDUP = CommandProperty(perm= 'e', arg_needed = False,
syntax="CDUP (go> to parentdirectory)."),
...
...
...
)

How does this strike you? With care, the comment and the table could
be kept aligned and nicely readable

cmd_data = dict(
# cmd = (perm, auth, arg, path, syntax),
ABOR = (None, False, False, False, "ABOR (abort transfer)."),
APPE = (None, False, False, True, "APPE <SP> file-name (append data to"),
...
]

ftpCommands = {}
for cmd,args in cmd_data.iteritems():
ftpCommands[cmd] = CommandProperty(*args)

Gary Herron

 

[Giampaolo Rodola']

Seems completely reasonable to me.  You might just consider using
keyword arguments in the __init__ method and eliminate the dictionary
altogether.

Not tested, but you will get the idea:

class CommandProperty:
    def __init__(self, perm = perm, auth_needed = True, arg_needed =
True,
                 check_path = False, syntax = syntax):

        self.perm = perm
        self.auth_needed = auth_needed
        self.arg_needed = arg_needed
        self.check_path = check_path
        self.syntax = syntax

ftpCommands = dict(
    ABOR = CommandProperty(perm = None, arg_needed = False,
             syntax="ABOR (abort transfer)."),
    APPE = CommandProperty(perm = 'a',  check_path=True,
             syntax = "APPE <SP> file-name (append data to" \
                      "an existent file)."),
    CDUP = CommandProperty(perm= 'e', arg_needed = False,
             syntax="CDUP (go> to parentdirectory)."),
...
...
...
    )

How does this strike you?    With care, the comment and the table could
be kept aligned and nicely readable

cmd_data = dict(
 # cmd = (perm, auth,   arg, path,   syntax),
 ABOR = (None, False, False, False, "ABOR (abort transfer)."),
 APPE  = (None, False, False, True,  "APPE <SP> file-name (append data to"),
 ...
]

ftpCommands = {}
for cmd,args in cmd_data.iteritems():
    ftpCommands[cmd] = CommandProperty(*args)

Gary Herron

IMHO this is a "little" easier to manage because you can take
advantage of the default values for keyword arguments to eliminate
some of the arguments.

Hope this helps,
Larry

- Mostra testo citato -- Nascondi testo citato

- Mostra testo citato -

Thanks, I didnt' know dict() could be used with =.
I think I'm going to use this solution.


--- Giampaolo
http://code.google.com/p/pyftpdlib/

 

[Paul Hankin]

Hi,
for an FTP server I wrote I'd need to group the FTP commands in one
table that defines the command itself, the syntax string, required
permission, whether it requires authorization, whether it takes
argument and whether there's a need to validate the path from the
argument.
The more obvious way I found to do that is something like this:

class CommandProperty:
    def __init__(self, perm, auth_needed, arg_needed, check_path,
syntax):
        self.perm = perm
        self.auth_needed = auth_needed
        self.arg_needed = arg_needed
        self.check_path = check_path
        self.syntax = syntax

ftp_cmds = {
    "ABOR" : CommandProperty(perm=None, auth_needed=True,
arg_needed=False, check_path=False, syntax="ABOR (abort transfer)."),
    "APPE" : CommandProperty(perm='a',  auth_needed=True,
arg_needed=True,  check_path=True,  syntax="APPE <SP> file-name
(append data to an existent file)."),
    "CDUP" : CommandProperty(perm='e',
auth_needed=True,arg_needed=False, check_path=False, syntax="CDUP (go
to parentdirectory)."),
    ...
    ...
    ...
    }

...but I find it somewhat redundant and... "ugly".
I was wondering if there was some kind of data type which could better
fit such purpose or if someone could suggest me some other approach to
do this same thing. Maybe using a dictionary is not the better choice
here.

How about something like this? The idea is to summarize the command
table, then construct the ftp command dictionary programatically from
it.

cmd_table = dict(
ABOR='-AR- (abort transfer)',
APPE='aARP <SP> file-name (append data to a file)',
CDUP='eA-- (go to parent directory)',
...
)

The first block of four characters give the options: permission,
whether authentication is needed, whether the argument is required,
and whether the path needs checking. Permission is the permission
letter or - (for none), A or - for authentication, R or - for argument
required, and - or P for path required. Then the help text follows
(with the command name omitted since it's redundant).

Turning these into CommandProperty's is straightforward (untested
code):

ftp_commands = {}
for cmd, descriptor in cmd_table.iteritems():
options, help = descriptor.split(' ', 1)
options = [None if opt == '-' else opt for opt in options]
perm, auth, arg, path = options
assert perm is None or perm in 'ae...'
assert auth is None or auth == 'A'
assert arg is None or arg == 'R'
assert path is None or path == 'P'
ftp_commands[cmd] = CommandProperty(perm=perm, auth_required=auth,
arg_required=arg, check_path=path, syntax = '%s %s' % (cmd, help))