Python Recipe: Read CSV/TSV Textfiles and Ignore Comment-lines

Scientific data commonly comes in tab-separated textfile format containing comment lines. What is the best way to read this data? Analogous to the recipe given by skip.montanaro, use a commented file decorator as follows:

import sys, re
import csv
class CommentedFile:
    def __init__(self, f, commentstring="#"):
        self.f = f
        self.commentstring = commentstring
    def next(self):
        line = self.f.next()
        while line.startswith(self.commentstring):
            line = self.f.next()
        return line
    def __iter__(self):
        return self

tsv_file = csv.reader(CommentedFile(open("inputfile.txt", "rb")),
                      delimiter='\t')
for row in tsv_file:
    print row[2] # prints column 3 of each line