title: Using unittest.mock to patch input() in Python 3
body: <p>How do you use the @patch decorator to patch the built-in input() function?</p>
  
  <p>For example, here's a function in question.py that I'd like to test, which contains a call to input():</p>
  
  <pre><code>def query_yes_no(question, default="yes"):
  """ Adapted from http://stackoverflow.com/questions/3041986/python-command-line-yes-no-input """
  
      valid = {"yes": True, "y": True, "ye": True, "no": False, "n": False}
      if default is None:
          prompt = " [y/n] "
      elif default == "yes":
          prompt = " [Y/n] "
      elif default == "no":
          prompt = " [y/N] "
      else:
          raise ValueError("invalid default answer: '%s'" % default)
  
      while True:
          sys.stdout.write(question + prompt)
          choice = input().lower()
  
          if default is not None and choice == '':
              return valid[default]
          elif choice in valid:
              return valid[choice]
          else:
              sys.stdout.write("Please respond with 'yes' or 'no' "
                               "(or 'y' or 'n').\n")
  </code></pre>
  
  <p>Here's my test, which gives me the error "ImportError: No module named '<strong>builtins</strong>'":</p>
  
  <pre><code>import unittest
  from unittest.mock import patch
  
  import question
  
  class TestQueryYesNo(unittest.TestCase):
  
      @patch('__builtins__.input.return_value', 'y')
      def test_query_y(self):
          answer = question.query_yes_no("Blah?")
          self.assertTrue(answer)
  </code></pre>