127 

   128 \begin{frame}[fragile]

   129   \frametitle{Functions}

   130   \begin{itemize}

   131     \item \kwrd{def} - keyword to define a function

   132     \item Arguments are local to a function

   133     \item Functions can return multiple values

   134   \end{itemize}

   135 \end{frame}

   136 

   137 \begin{frame}[fragile]

   138   \frametitle{Functions: example}

   139   \begin{lstlisting}

   140 def signum( r ):

   141     """returns 0 if r is zero

   142     -1 if r is negative

   143     +1 if r is positive"""

   144     if r < 0:

   145         return -1

   146     elif r > 0:

   147         return 1

   148     else:

   149         return 0

   150   \end{lstlisting}

   151   \emphbar{Note docstrings}

   152 \end{frame}

   153 

   154 \begin{frame}[fragile]

   155   \frametitle {What does this function do?}

   156   \begin{lstlisting}

   157 def what( n ):

   158     if n < 0: n = -n

   159     while n > 0:

   160         if n % 2 == 1:

   161             return False

   162         n /= 10

   163     return True

   164   \end{lstlisting}

   165 \end{frame} 

   166 

   167 \begin{frame}[fragile]

   168   {What does this function do?}

   169 \begin{lstlisting}

   170 def what( n ):

   171     i = 1

   172     while i * i < n:

   173         i += 1

   174     return i * i == n, i

   175   \end{lstlisting}

   176 \end{frame}

   177 

   178 \begin{frame}[fragile]

   179   \frametitle {What does this function do?}

   180   \begin{lstlisting}

   181 def what( x, n ):

   182     if n < 0: 

   183        n = -n

   184        x = 1.0 / x

   185 

   186     z = 1.0

   187     while n > 0:

   188         if n % 2 == 1:

   189             z *= x

   190         x *= x

   191         n /= 2

   192     return z

   193   \end{lstlisting}

   194 \end{frame} 

   195