title: Finding keys for a value in a dictionary of integers
body: <p>The problem is to write a Python function that returns a list of keys in aDict with the value target. All keys and values in the dictionary are integers and the keys in the list we return must be in increasing order.</p>
  
  <p>This is the work I have so far:</p>
  
  <pre><code>def keysWithValue(aDict, target):
      '''
      aDict: a dictionary
      target: an integer
      '''
      ans = []
      if target not in aDict.values():
          return ans
      else:
          for key in aDict.keys():
              if target in aDict[key]:
                  ans+=[key]
          return ans.sort()
  </code></pre>
  
  <p>I keep on getting:</p>
  
  <blockquote>
    <p>"TypeError: argument of type 'int' is not iterable"</p>
  </blockquote>
  
  <p>but I don't really understand what that means, and how to fix it. If anyone could help, I'd be really grateful!</p>