extractor.py

#!/usr/bin/env python
"""
Extract and print network addresses from a file.

This was written for Python 3.x because Python 2.x is a decade old, and every
time you use it, Baby Guido cries.

If you have an older python, download the Miniconda Python installer at
http://conda.pydata.org/miniconda.html, run it, and load a new shell.

If you installed Miniconda for Python 2.x, create a Python 3.x environment:

    conda create -n py2 python=2
    source activate py2

Alternatively, you can just clone github.com/princebot/pythonize and run this:

    pythonize --miniconda --version 3

Or, if you reaaally want, you can just ask, and I’ll make you a py2 version. ^.^

"""

import ipaddress
import json
import sys


def extract_network_objects(text):
    """Return a list of network objects from input text."""
    try:
        data = json.loads(text)
    except json.DecodeError:
        return None
    ips = []
    for subnet in data['subnets']:
        address = subnet.get('range_end')
        mask_bits = subnet.get('mask_bits')
        network = '{}/{}'.format(address, mask_bits)
        try:
            ips.append(ipaddress.ip_network(network, strict=False))
        except ValueError:
            continue
    return ips or None


# extract_network_strings is just an example of how to do this without the
# ipaddress library: extract_network_objects is the function that main will
# actually use.

def extract_network_strings(text):
    """Return a list of strings describing networks in CIDR format."""
    try:
        data = json.loads(text)
    except json.DecodeError:
        return None
    ips = []
    for subnet in data['subnets']:
        address = subnet.get('network')
        mask_bits = subnet.get('mask_bits')
        ips.append('{}/{}'.format(address, mask_bits))
    return ips or None


def die(message):
    """Print an error message then exit."""
    print(message, file=sys.stderr)
    sys.exit(1)


if __name__ == '__main__':
    if len(sys.argv) < 2:
        die("error: no file argument")
    input_file = sys.argv[1]
    try:
        with open(input_file) as f:
            file_contents = f.read()
    except OSError:
        die("error: cannot read input file {}".format(input_file))
    ips = extract_network_objects(file_contents)
    if ips is None:
        die("error: no networks found in input file")
    for ip in ips:
        print(ip)