How to use csv.Sniffer for 2 different CSV-types?

I want to read 2 different types of CSV-files:

• one with a ',' as delimiter
• one with a ';' as delimiter

I tried to check which delimiter I'm using by doing:

dialect = csv.Sniffer().sniff(csvfile, [',', ';'])  
data = csv.reader(csvfile, dialect)

but then I get the TypeError : expected string or buffer.

If I do this, it works, but then I don't know when to use what delimiter.

data = csv.reader(csvfile, delimiter = ",")  
data = csv.reader(csvfile, delimiter = ";")

Can someone help me please?