boolean.txt
+--

Booleans

 bool type has values True, False

 Used in  if b: ...  # do body once,  while b: ...  # do body repeatedly

 Other types are interpreted as True, False in boolean context (tests)
  nonzero, zero    # numeric types
  nonempty, empty  # collection types
  (other), None    # any types

 assert statement tests Boolean expression, exits program with message if False
   assert isinstance(s, list) and len(s) > 0 # document assumptions, intent

 assert can be turned off with python -o switch

 (aside: assertions can be the basis for a proof of correctness)






+--

Block structure

 Block starts after colon, indent indicates block, outdent exits:

   if b:
      ...  # execute indented section only if b is True
      ...
   ...     # jump here if b is False
   ...

 Used for all block structure in Python: alternative to begin, end, {, }, ;, ...

 Line break ends statement, use \ to extend line, not needed inside (...), [...]

 








+--

Booleans -- style

 Booleans are values!  You can return bool variables etc.

 Style
 
   Unnecessary         Sufficient
   -----------         ----------

   if b == True:       if b:
    ...                 ...



   Maybe wrong         Correct
   -----------         -------
   ...                 ...
   if b:               return b
     return True