title: FLAGS = None meaning?
body: <p>I am new to python &amp; tensorFlow, and I am following <a href="https://github.com/tensorflow/tensorflow/blob/master/tensorflow/examples/tutorials/mnist/mnist_softmax.py" rel="noreferrer">this MNIST tutorial</a> on tensorFlow documentation. </p>
  
  <p>In the first bit, I don't know what FLAGS = None does here. I searched in Google, and came back empty. Seems like this is too obvious to others? </p>
  
  <pre><code>from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  
  import argparse
  import sys
  
  from tensorflow.examples.tutorials.mnist import input_data
  
  import tensorflow as tf
  
  FLAGS = None
  
  
  def main(_):
    # Import data
    mnist = input_data.read_data_sets(FLAGS.data_dir, one_hot=True)
  </code></pre>
  
  <p>So what is FLAGS and how it is used? 
  e.g., FLAGS.data_dir</p>
  
  <p>Any help would be appreciated!</p>