1 \frametitle {Why are they useful?}

     2   \small

     3   \begin{lstlisting}

     4 for element in (1, 2, 3):

     5     print element

     6 for key in {'one':1, 'two':2}:

     7     print key

     8 for char in "123":

     9     print char

    10 for line in open("myfile.txt"):

    11     print line

    12 for line in urllib2.urlopen('http://site.com'):

    13     print line

    14   \end{lstlisting}