def alias_magic(self, line=''):
        """Create an alias for an existing line or cell magic.

        Examples
        --------
        ::

          In [1]: %alias_magic t timeit
          Created `%t` as an alias for `%timeit`.
          Created `%%t` as an alias for `%%timeit`.

          In [2]: %t -n1 pass
          1 loops, best of 3: 954 ns per loop

          In [3]: %%t -n1
             ...: pass
             ...:
          1 loops, best of 3: 954 ns per loop

          In [4]: %alias_magic --cell whereami pwd
          UsageError: Cell magic function `%%pwd` not found.
          In [5]: %alias_magic --line whereami pwd
          Created `%whereami` as an alias for `%pwd`.

          In [6]: %whereami
          Out[6]: u'/home/testuser'