Elegant way to skip first line when using python fileinput module?

Question

Is there an elegant way of skipping first line of file when using python fileinput module?

I have data file with nicely formated data but the first line is header. Using fileinput I would have to include check and discard line if the line does not seem to contain data.

The problem is that it would apply the same check for the rest of the file. With read() you can open file, read first line then go to loop over the rest of the file. Is there similar trick with fileinput?

Is there an elegant way to skip processing of the first line?

Example code:

import fileinput

# how to skip first line elegantly?

for line in fileinput.input(["file.dat"]):
    data = proces_line(line);
    output(data)

Answer 1

lines = iter(fileinput.input(["file.dat"]))
next(lines) # extract and discard first line
for line in lines:
    data = proces_line(line)
    output(data)

or use the itertools.islice way if you prefer

import itertools
finput = fileinput.input(["file.dat"])
lines = itertools.islice(finput, 1, None) # cuts off first line
dataset = (process_line(line) for line in lines)
results = [output(data) for data in dataset]

Since everything used are generators and iterators, no intermediate list will be built.

Answer 2

The fileinput module contains a bunch of handy functions, one of which seems to do exactly what you're looking for:

for line in fileinput.input(["file.dat"]):
  if not fileinput.isfirstline():
    data = proces_line(line);
    output(data)

fileinput module documentation

Answer 3

It's right in the docs: http://docs.python.org/library/fileinput.html#fileinput.isfirstline