new_contents: ### The Lovely Python WITH
  
  `with` is a python statement that encapsulates a class that runs a function and "tears it down". An example of this pattern would be opening and closing a file.
  
  In longhand, this would could look like
  
  ```python
  def controlled_execution(callback):
    set things up
    try:
      callback(thing)
    finally:
      tear things down
  
  def my_function(thing):
    do something
  
  controlled_execution(my_function)
  ```
  
  This is verbose.
  
  ```python
  class controlled_execution:
    def __enter__(self): # "context guard" assigns whatever __enter__ returns to the variable given by as
      set things up
      return thing
  
    def __exit__(self, type, value, traceback):
      tear things down
  
  with controlled_execution() as thing:
    some code
  ```
  In Python 2.5, the file object has been equipped with `__enter__` and `__exit__` methods. The former return the file object, and the latter closes the file.
  
subject: add things about with