title: Python Count Elements in a List of Objects with Matching Attributes
body: <p>I am trying to find a simple and fast way of counting the number of Objects in a list that match a criteria.
  e.g.</p>
  
  <pre><code>class Person:
      def __init__(self, Name, Age, Gender):
          self.Name = Name
          self.Age = Age
          self.Gender = Gender
  
  # List of People
  PeopleList = [Person("Joan", 15, "F"), 
                Person("Henry", 18, "M"), 
                Person("Marg", 21, "F")]
  </code></pre>
  
  <p>Now what's the simplest function for counting the number of objects in this list that match an argument based on their attributes?
  E.g., returning 2 for Person.Gender == "F" or Person.Age &lt; 20.</p>