#!/usr/bin/env python

The first line in this file is the "shebang" line.  When you execute a file
from the shell, the shell tries to run the file using the command specified
on the shebang line.  The ! is called the "bang".  The # is not called the
"she", so sometimes the "shebang" line is also called the "hashbang".
The hash character is used because it defines a comment in most scripting
languages, so the shebang line will be ignored by the scripting language
by default.
The shebang line was invented because scripts are not compiled, so they are
not executable files, but people still want to "run" them.  The shebang
line specifies exactly how to run a script.  In other words, this shebang
line says that, when I type in ./basics.py, the shell will actuall run
  /usr/bin/env python basics.py
We use
  #!/usr/bin/env python
instead of
  #!/usr/bin/python
because we must specify an absolute path to a program, and /usr/bin/env
is a utility that uses the user's path to run an application (in this
case, python).  Thus, it's more portable.

More on shebang lines, including portability:
http://en.wikipedia.org/wiki/Shebang_(Unix)

If you don't like this basic walk through python, check out
http://docs.python.org/tutorial/
or
http://diveintopython.org/