• Destructors in Python are not guaranteed to run. __del__ (finalizer; when garbage collector garbage collects)
• Duck Typing: if an object has the requested method, a call to it will just work
  • “If it quacks like a duck, then it must be a duck”
• Checking if not None, obj is not None
• arr += [9] is the same as arr.append(9), but not the same as arr = arr + [9]
• Dictionaries have a separate array that keeps track of insertion order