title: Flask reqparse.RequestParser ValueError with parse_args()
body: <p>Good day everyone,</p>
  <p>I am having a really strange issue with Flask's <code>RequestParser.parse_args()</code>. Below is a snippet of my <code>__init__</code> method of the relevant class:</p>
  <pre><code>def __init__(self, arg1, arg2):
      self.arg1 = arg1
      self.arg2 = arg2
      self.arg_parser = reqparse.RequestParser()
      self.arg_parser.add_argument('optional_arg_from_url', type=bool, default=False)
  </code></pre>
  <p>Notice I only add 1 argument to <code>self.arg_parser</code>. Then, in the <code>post</code> method, I want to retrieve <code>optional_arg_from_url</code> with <code>arg_parser.parse_args()</code> as follows:</p>
  <pre><code>def post(self):
  
      # Authorization in headers
      token = request.headers.get('Authorization').split()[1]
  
      # Parse args
      args = self.arg_parser.parse_args()
      optional_arg_from_url = args['optional_arg_from_url']
  </code></pre>
  <p>Now, an example of the request url containing the optional arg would look as follows:</p>
  <p><code>http://localhost:8080/path/to/endpoint/?optional_arg_from_url=True</code></p>
  <p>The error that I am getting is <code>ValueError: not enough values to unpack: expected 2</code>, which is raised when <code>args = self.arg_parser.parse_args()</code> is called. I don't understand why 2 values are expected, since I only add one argument to the parser. Also, why would a value error be raised when I try to parse the args? Shouldn't it just parse all the args regardless?</p>
  <p>Another interesting thing, is that the corresponding unit tests are working, regardless of whether the optional arg is included in the url or not. The code ALSO works if I do not include the optional arg in the url (which means the arg defaults to <code>False</code>) and gets parsed correspondingly. It is just when I try to overwrite the arg's value to <code>True</code> within the request url when a value error is raised.</p>
  <p>I also made sure that <code>optional_arg_from_url</code> is spelled exactly the same everywhere, so that is not the issue.</p>
  <p>Any assistance is appreciated.</p>