iPython magic

iPython supports a number of magic commands that can make your life easier. There are two types of them: line magics and cell magics. Line magics start with % sign, %timeit is a good example:

In [1]: %timeit sum(x**2 for x in range(1000))
243 µs ± 2.31 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)

Cell magics start with double % sign, look at %%ruby:

In [2]: %%ruby
   ...: 3.times do |x|
   ...:   puts x
   ...: end
   ...:
0
1
2

You can even define custom magics. This is an example magic that helps you ignore an expression result except the very end:

In [3]: from IPython.core.magic import register_line_magic

In [4]: @register_line_magic
   ...: def tail(line):
   ...:     result = repr(eval(line))
   ...:     if len(result) > 100:
   ...:         return '... {}'.format(result[-100:])
   ...:

In [5]: %tail list(range(1000))
Out[5]: '...  980, 981, 982, 983, 984, 985, 986, 987, 988, 989, 990, 991, 992, 993, 994, 995, 996, 997, 998, 999]'

All that is also true for Jupyter Notebook.