Option 1: Python, using eppy:

In [1]:
import eppy.EPlusInterfaceFunctions.parse_idd as parse_idd

iddfile = "/Applications/EnergyPlus-8-6-0/Energy+.idd"
IDF.setiddname(iddfile)

x = parse_idd.extractidddata(iddfile)

useful = x[2]

The most useful (IMHO) is the second element of the 4-tuple x

That's a list of each idd object, each idd object being a list of dict where the first element (index 0) is the object itself, and the following are each field.

Example:

In [2]: useful[6]
Out[2]:
[{'format': ['singleLine'],
  'group': 'Simulation Parameters',
  'idfobj': 'SurfaceConvectionAlgorithm:Inside',
  'memo': ['Default indoor surface heat transfer convection algorithm to be used for all zones'],
  'unique-object': ['']},
 {'default': ['TARP'],
  'field': ['Algorithm'],
  'key': ['Simple', 'TARP', 'CeilingDiffuser', 'AdaptiveConvectionAlgorithm'],
  'note': ['Simple = constant value natural convection (ASHRAE)',
   'TARP = variable natural convection based on temperature difference (ASHRAE, Walton)',
   'CeilingDiffuser = ACH-based forced and mixed convection correlations',
   'for ceiling diffuser configuration with simple natural convection limit',
   'AdaptiveConvectionAlgorithm = dynamic selection of convection models based on conditions'],
  'type': ['choice']}]

Here's a way you would print each object and their fields (there's much more info) for the first few objects of the idd

In [3]:
for k in useful[2:5]:
    print(k[0]['idfobj'])
    for j in k[1:]:
        print("---- {}".format(j['field'][0]))

Out[3]:
Version
---- Version Identifier
SimulationControl
---- Do Zone Sizing Calculation
---- Do System Sizing Calculation
---- Do Plant Sizing Calculation
---- Run Simulation for Sizing Periods
---- Run Simulation for Weather File Run Periods
---- Do HVAC Sizing Simulation for Sizing Periods
---- Maximum Number of HVAC Sizing Simulation Passes
Building
---- Name
---- North Axis
---- Terrain
---- Loads Convergence Tolerance Value
---- Temperature Convergence Tolerance Value
---- Solar Distribution
---- Maximum Number of Warmup Days
---- Minimum Number of Warmup Days

Option 2: Ruby, using OpenStudio

This will print each object and its field, as well as save it into a hash (key = idd object name, value = list of fields)

h = {}

factory = OpenStudio::IddFileAndFactoryWrapper.new("EnergyPlus".to_IddFileType)
factory.objects.each do |obj|
  n = obj.numFields
  l = []
  puts obj.name.to_s
  obj.nonextensibleFields.each do |field|
    puts "---- #{field.name.to_s}"
    l << field.name.to_s
  end
  if l.length < n
    puts "ERROR, missing fields"
  end
  h[obj.name.to_s] = l
end

Of course you can access more info out of each field, for example field.properties.required, field.properties.note, field.properties.units.get, etc, etc

Option 3: using the new JSON input dictionary (JDD), using either Python or Ruby

E+ 8.7 release is in preparation and will include a new "JDD" for JSON input Data Dictionary, the JSON equivalent of the IDD. Currently this is on a separate development branch, but here's the input_processor_refactor/idd/Energy+.jdd.in.

I'm gonna propose a Python and a Ruby version to parse this file, print the fields for each object as well as store a simple dict/hash where the key is the object type, and the value is a list of the fields for each object. Of course, there's way more information in the JDD, use it as you want.

3.a Python

import json
import urllib.request 

jdd_url ...