review_2.txt - week 2 review
+--

Python

 Distinguish capital-P Python language, small-p python interpreter (program)

 Several Python language versions (we use 2.x not 3), python interpreters (CPython)

 python interpreter can be interactive calculator/prototyper with built-in help
  dir()  help()  dir(x)  help(x) 

 python interpreter can execute Python programs non-interactively (lots of ways)

 Python programs are stored in modules: files that end in .py, contain Python code

 Python import statement loads, executes modules into python interpreter
  works the same in interactive session or non-interactive command

 Python development uses python interpreter and Python-aware editor for modules

 Integrated development environment (like IDLE) integrates both, adds conveniences








+--

Values, types, expressions, statements

 Values are pieces of data: 42, 'Hello, world' ...

 In Python all values are objects (lots going on behind the curtain!)

 Values belong to types (examples: string vs. int, can be subtle, int vs. float)

 Expressions combine values with operators, compute new values, no other effects
   2+2    2*3  'Hello ' + 'world'   'Hello'*3

 Statements (print, assign) contain expressions, have effects (output, storage)
   print 2+2 # effect is output     x = 2+2  # effect is storage

 Syntax errors - appearance - checked at compile time
   2 + ((3)

 Type errors - meaning - types not consistent with operators - checked at run time
   2 + '3'

 Python functions for types: 
  queries: type(2)  type('3')  tests: isinstance('3',int)  conversions: 2+int('3')