Help understanding code

[Dhruva Hein]

Hi. I am trying to understand a section of code written for Plone and I 
am having problems understanding the Python syntax in a few of the 
following lines.

I'd be grateful if someone could help me understand what's happening in 
the lines I've marked. I can't see how the dictionary is built or how 
the lists ['bytype'][cytype] make sense in python.

Thanks in advance.
class Stats:
  def getContentTypes(self):
      """ Returns the number of documents by type """
      pc = getToolByName(self, "portal_catalog")
      # call the catalog and loop through the records
      results = pc()                                                   
              <=== what is the difference between pc and pc()?
      numbers = {"total":len(results),"bytype":{},"bystate":{}} <=== 
This is hard to understand
      for result in results:
          # set the number for the type
          ctype = str(result.Type)
          num = numbers["bytype"].get(ctype, 0)  <==== where does .get 
come from? and what is the string 'bytype' doing?
          num += 1
          numbers["bytype"][ctype] = num    <====== is this some kind 
of an array?

          # set the number for the state
          state = str(result.review_state)
          num = numbers["bystate"].get(state, 0)
          num += 1
          numbers["bystate"][state] = num
      return numbers
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