I'm trying to load a CSV file to Amazon S3 with Python. I need to know CSV file's modification time. I'm using ftplib to connect FTP with Python (2.7).

回答1:

MLST or MDTM

While you can retrieve a timestamp of an individual file over FTP with MLST or MDTM commands, neither is supported by ftplib.

Of course you can implement the MLST or MDTM on your own using FTP.voidcmd.

See:

3. File Modification Time (MDTM)
7. Listings for Machine Processing (MLST and MLSD)

A simple example for MDTM:

from ftplib import FTP
from dateutil import parser

# ... (connection to FTP)

timestamp = ftp.voidcmd("MDTM /remote/path/file.txt")[4:].strip()

time = parser.parse(timestamp)

print(time)

MLSD

The only command explicitly supported by the ftplib library that can return standardized file timestamp is MLSD via FTP.mlsd method. Though its use makes sense only if you want to retrieve timestamps for more files.

Retrieve a complete directory listing using MLSD
Search the returned collection for the file(s) you want
Retrieve modify fact
Parse it according to the specification, YYYYMMDDHHMMSS[.sss]

For details, refer to RFC 3659, particularly the:

7.5.3. The modify Fact section
2.3. Times section

from ftplib import FTP
from dateutil import parser

# ... (connection to FTP)

files = ftp.mlsd("/remote/path")

for file in files:
    name = file[0]
    timestamp = file[1]['modify']
    time = parser.parse(timestamp)
    print(name + ' - ' + str(time))

Note that times returned by MLST, MLSD and MDTM are in UTC (unless the server is broken). So you may need to correct them for your local timezone.

Again, refer to RFC 3659 2.3. Times section:

Time values are always represented in UTC (GMT), and in the Gregorian calendar regardless of what calendar may have been in use at the date and time indicated at the location of the server-PI.

LIST

If the FTP server does not support any of MLST, MLSD and MDTM, all you can do is to use an obsolete LIST command. That involves parsing a proprietary listing it returns.

A common *nix listing is like:

-rw-r--r-- 1 user group           4467 Mar 27  2018 file1.zip
-rw-r--r-- 1 user group         124529 Jun 18 15:31 file2.zip

With a listing like this, this code will do:

from ftplib import FTP
from dateutil import parser

# ... (connection to FTP)

lines = []
ftp.dir("/remote/path", lines.append)

for line in lines:
    tokens = line.split(maxsplit = 9)
    name = tokens[8]
    time_str = tokens[5] + " " + tokens[6] + " " + tokens[7]
    time = parser.parse(time_str)
    print(name + ' - ' + str(time))