Python inserting variable string as file name

I'm trying to create a file with a unique file name for every time my script runs. I am only intending to do this to every week or month. so I chose to use the date for the file name.

f = open('%s.csv', 'wb') %name

is where I'm getting this error.

Traceback (most recent call last):
File "C:\Users\User\workspace\new3\stjohnsinvoices\BabblevoiceInvoiceswpath.py", line 143,      in <module>
f = open('%s.csv', 'ab') %name
TypeError: unsupported operand type(s) for %: 'file' and 'str'

it works if I use a static filename, is there an issue with the open function, that means you can't pass a string like this?

name is a string and has values such as :

31/1/2013BVI

Many thanks for any help.

You need to put % name straight after the string:

f = open('%s.csv' % name, 'wb')

The reason your code doesn't work is because you are trying to % a file, which isn't string formatting, and is also invalid.

you can do something like

filename = "%s.csv" % name
f = open(filename , 'wb')

or f = open('%s.csv' % name, 'wb')

And with the new string formatting method...

f = open('{0}.csv'.format(name), 'wb')

Very similar to peixe.
You don't have to mention the number if the variables you add as parameters are in order of appearance

f = open('{}.csv'.format(name), 'wb')

Another option - the f-string formatting (ref):

f = open(f"{name}.csv", 'wb') 

Even better are f-strings in python 3!

f = open(f'{name}.csv', 'wb')