json2path.py

#!/usr/bin/env python

import json
import sys

def pp(vv, prefix='$'): # vv = array w/ JSON data, prefix = what's printed at the start of each line
    if isinstance(vv, (list,tuple)): # if vv is a list/tuple - an Array in Ruby
        for i, v in enumerate(vv): # vv being enumerated means each array element
                                   # is being given an "index", so (a, b, c) => [(0, a), (1, b), (2, c)]...
                                   # so for each "index" & "value" pair of the enumerated vv array...
            pp(v, "{0}[{1}]".format(prefix, i)) # the pp method is called again, only on
                                                # the "values"... and I don't get the second part -
                                                # one element is printed in square brackets, but which one?
    elif isinstance(vv, dict):                  # if vv is a dict - a Hash in Ruby
        for k,v in sorted(vv.items()):          # then for each key&value pair in that sorted Hash
            pp(v, "{0}.{1}".format(prefix, k))  # the pp method is called again
                                                # and the key&value is printed separated by a "."?
    else:                                                # the `else` case prints out the value after
        print '{0} = {1}'.format(prefix, json.dumps(vv)) # an `=` sign when there's no nested hash/array left

pp(json.load(sys.stdin))

Line #11 in Ruby would be "#{prefix}[#{i}]" - prefix, then index in square brackets. This makes each element of a sequence (array/list/tuple) printed with an index attached to the prefix; if prefix = 'foo'``, andvv = ['a','b','c']`, the the output would be:

foo[0] = "a" # v='a', i=0, prefix='foo' -> pp('a', 'foo[0]')
foo[1] = "b" # v='b', i=1, prefix='foo' -> pp('b', 'foo[1]')
foo[2] = "c" # v='c', i=2, prefix='foo' -> pp('c', 'foo[2]')

It's similar for the dictionaries in line 16 - pp is called recursively, with vv set to value, and the lower prefix set to "#{prefix}.#{key}" to give dotted notation.

The line 19, at the leaves of the JSON data tree (when the value provided to pp is an atom - a single piece of data, not a sequence or a dictionary, where we cannot recurse deeper), is the only one that actually prints anything to the screen - the final prefix, and value (encoded as JSON to quote any special characters, such as newlines).