% operator in python over string

Question

What does the following Python statement mean?

send_data=""
str_len = "%#04d" % (len(send_data)/2)

Answer 1

http://www.python.org/doc/2.5.2/lib/typesseq-strings.html

Answer 2

This sets str_len to show half the length of send_data, padded with zeros to be four characters right. The % character is carrying out interpolation. See the references provided by others.