Use Python to remove lines in a files that start with an octothorpe?

python startswith
drbunsen picture drbunsen · Aug 8, 2011 · Viewed 27.4k times · Source

This seems like a straight-forward question but I can't seem to pinpoint my problem. I am trying to delete all lines in a file that start with an octothorpe (#) except the first line. Here is the loop I am working with:

for i, line in enumerate(input_file):
    if i > 1:
        if not line.startswith('#'):
            output.write(line)

The above code doesn't seem to work. Does anyone known what my problem is? Thanks!

Answer

Ned Batchelder picture Ned Batchelder · Aug 8, 2011

You aren't writing out the first line:

for i, line in enumerate(input_file):
    if i == 0:
        output.write(line)
    else:
        if not line.startswith('#'):
            output.write(line)

Keep in mind also that enumerate (like most things) starts at zero.

A little more concisely (and not repeating the output line):

for i, line in enumerate(input_file):
    if i == 0 or not line.startswith('#'):
        output.write(line)

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