#  You can read about the changes in [What's New In Python
#  3.0](http://docs.python.org/3.0/whatsnew/3.0.html). You should read it
#  thoroughly when you move from 2.x to 3.x since a lot has been changed.
#  
#  The whole answer here are quotes from the documentation.
#  
#  **[Views And Iterators Instead Of
#  Lists](http://docs.python.org/3.0/whatsnew/3.0.htmlviews-and-
#  iterators-instead-of-lists)**
#  
#  > Some well-known APIs no longer return lists:
#  >
#  > - [...]
#  > - [`map()`](http://docs.python.org/3.0/library/functions.htmlmap)
#  and
#  [`filter()`](http://docs.python.org/3.0/library/functions.htmlfilter)
#  return iterators. If you really need a list, a quick fix is e.g.
#  `list(map(...))`, but a better fix is often to use a list
#  comprehension (especially when the original code uses lambda), or
#  rewriting the code so it doesn’t need a list at all. Particularly
#  tricky is `map()` invoked for the side effects of the function; the
#  correct transformation is to use a regular `for` loop (since creating
#  a list would just be wasteful).
#  > - [...]
#  
#  **[Builtins](http://docs.python.org/3.0/whatsnew/3.0.htmlbuiltins)**
#  
#  > - [...]
#  > - Removed `reduce()`. Use [`functools.reduce()`](http://docs.python.
#  org/3.0/library/functools.htmlfunctools.reduce) if you really need
#  it; however, 99 percent of the time an explicit `for` loop is more
#  readable.
#  > - [...]
#  
#  [nhahtdh] [so/q/13638898] [cc by-sa 3.0]