Context manager: with for file

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examples/advanced/with_file.py

import sys

if len(sys.argv) != 2:
    sys.stderr.write('Usage: {} FILENAME\n'.format(sys.argv[0]))
    exit()

file = sys.argv[1]
print(file)
with open(file) as f:
    for line in f:
        val = 30/int(line)

print('done')