title: Filtering Characters from a String
body: <p>I need to make a function that takes two strings as imnput and returns a copy of str 1 with all characters from str2 removed.     </p>
  
  <p>First thing is to iterate over str1 with a for loop, then compare to str2, to accomplish subtraction I should create a 3rd string in which to store the output but I'm a little lost after that.</p>
  
  <pre><code>def filter_string(str1, str2):
      str3 = str1   
      for character in str1:
         if character in str2:
             str3 = str1 - str2
      return str3
  </code></pre>
  
  <p>This is what I've been playing with but I don't understand how I should proceed. </p>