How to check empty gzip file in Python

Question

I don\'t want to use OS commands as that makes it is OS dependent.

This is available in tarfile, tarfile.is_tarfile(filename), to check if

Answer 1

Looking through the source code for the Python 2.7 version of the gzip module, it seems to immediately return EOF, not only in the case where the gzipped file is zero bytes, but also in the case that the gzip file is zero bytes, which is arguably a bug.

However, for your particular use-case, we can do a little better, by also confirming the gzipped file is a valid CSV file.

This code...

import csv
import gzip

# Returns true if the specified filename is a valid gzip'd CSV file
# If the optional 'columns' parameter is specified, also check that
# the first row has that many columns
def is_valid(filename, columns=None):

    try:

        # Chain a CSV reader onto a gzip reader
        csv_file = csv.reader(gzip.open(filename))

        # This will try to read the first line
        # If it's not a valid gzip, this will raise IOError
        for row in csv_file:

            # We got at least one row
            # Bail out here if we don't care how many columns we have
            if columns is None:
                return True

            # Check it has the right number of columns
            return len(row) == columns

        else:

            # There were no rows
            return False

    except IOError:

        # This is not a valid gzip file
        return False


# Example to check whether File.txt.gz is valid
result = is_valid('File.txt.gz')

# Example to check whether File.txt.gz is valid, and has three columns
result = is_valid('File.txt.gz', columns=3)

...should correctly handle the following error cases...

1. The gzip file is zero bytes
2. The gzip file is not a valid gzip file
3. The gzipped file is zero bytes
4. The gzipped file is not zero bytes, but contains no CSV data
5. (Optionally) The gzipped file contains CSV data, but with the wrong number of columns