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