Amend a csv file in Python

Question

So I have a CSV file with a bunch on IP's in it:

192.168.0.1,192.168.0.2,192.168.0.3,192.168.0.4,192.168.0.5,192.168.0.6,192.168.0.7,192.168.0.8,192.168.0.9,192.168.0.10

And I would like to add a new ip to the end of this csv file. Currently I am using this code to read in the data:

requests = csv.reader(open("file.csv", "rb"))
for request in requests:
 for ip in request:
 print "In List: " + str(ip)

This will print:

In List: 192.168.0.1
In List: 192.168.0.2
In List: 192.168.0.3
In List: 192.168.0.4
In List: 192.168.0.5
...

And then to write one to the end I've tried many methods, including this:

requestWriter = csv.writer(open("file.csv", "w"))
requestWriter.writerow(["192.168.0.X"])

This however replaces the whole file with the new entry. I then tried to loop through existing records and add them to the new file but this split the IP's up by their .'s! Am I missing something here? Surely there is an amend option for the csv reader/writer?

Thanks

• systempuntoout: You are not developing in Windows, isn't it? Because "rb" means read+binary and csv is tipically not binary. This probably works because you are developing on a system that does not differentiate between binary and text files (ie b has no effect).
• S.Lott: "and csv is typically not binary". Since for Windows it is binary, it's simpler to open CSV with "wb" to assure compatibility.
• systempuntoout: @S.Lott uh, csv is binary in Windows?
• S.Lott: @systempuntoout: In an obscure way, yes. From docs.python.org/library/csv.html#csv.writer. "If csvfile is a file object, it must be opened with the ‘b’ flag on platforms where that makes a difference." And the platform where it makes a difference is? You guessed it. Windows.
• S.Lott: -1: "I can't really disclose what system I'm working on". Can't possibly be true unless it was a seekrit custom-built operating system where disclosure of status as the only client would somehow violate national security. Otherwise, it's difficult to be sure of an answer when there's this kind of refusal to disclose basic facts.

Answer 1

Why don't you just append a new row?

fd = open('file.csv','a')
fd.write(yourCsvRowWithNewIP)
fd.close()

• kevingessner: @ing0: You can still use the CSV writer; the important part is opening the file with mode 'a'. See docs.python.org/library/functions.html#open
• Aaron Digulla: @systempuntoout: Don't forget the comma!
• ingh.am: @aaron It's ok, I didn't forget! :)