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`View the original notebook on nbviewer <http://nbviewer.jupyter.org/github/jupyter/notebook/blob/master/docs/source/examples/Notebook/Running%20Code.ipynb>`__
Running Code
============
First and foremost, the Jupyter Notebook is an interactive environment
for writing and running code. The notebook is capable of running code in
a wide range of languages. However, each notebook is associated with a
single kernel. This notebook is associated with the IPython kernel,
therefor runs Python code.
Code cells allow you to enter and run code
------------------------------------------
Run a code cell using ``Shift-Enter`` or pressing the
.. raw:: html
<button class="btn btn-default btn-xs">
.. raw:: html
</button>
button in the toolbar above:
.. code:: python
a = 10
.. code:: python
print(a)
There are two other keyboard shortcuts for running code:
- ``Alt-Enter`` runs the current cell and inserts a new one below.
- ``Ctrl-Enter`` run the current cell and enters command mode.
Managing the Kernel
-------------------
Code is run in a separate process called the Kernel. The Kernel can be
interrupted or restarted. Try running the following cell and then hit
the
.. raw:: html
<button class="btn btn-default btn-xs">
.. raw:: html
</button>
button in the toolbar above.
.. code:: python
import time
time.sleep(10)
If the Kernel dies you will be prompted to restart it. Here we call the
low-level system libc.time routine with the wrong argument via ctypes to
segfault the Python interpreter:
.. code:: python
import sys
from ctypes import CDLL
# This will crash a Linux or Mac system
# equivalent calls can be made on Windows
dll = 'dylib' if sys.platform == 'darwin' else 'so.6'
libc = CDLL("libc.%s" % dll)
libc.time(-1) # BOOM!!
Cell menu
---------
The "Cell" menu has a number of menu items for running code in different
ways. These includes:
- Run and Select Below
- Run and Insert Below
- Run All
- Run All Above
- Run All Below
Restarting the kernels
----------------------
The kernel maintains the state of a notebook's computations. You can
reset this state by restarting the kernel. This is done by clicking on
the
.. raw:: html
<button class="btn btn-default btn-xs">
.. raw:: html
</button>
in the toolbar above.
sys.stdout and sys.stderr
-------------------------
The stdout and stderr streams are displayed as text in the output area.
.. code:: python
print("hi, stdout")
.. code:: python
from __future__ import print_function
print('hi, stderr', file=sys.stderr)
Output is asynchronous
----------------------
All output is displayed asynchronously as it is generated in the Kernel.
If you execute the next cell, you will see the output one piece at a
time, not all at the end.
.. code:: python
import time, sys
for i in range(8):
print(i)
time.sleep(0.5)
Large outputs
-------------
To better handle large outputs, the output area can be collapsed. Run
the following cell and then single- or double- click on the active area
to the left of the output:
.. code:: python
for i in range(50):
print(i)
Beyond a certain point, output will scroll automatically:
.. code:: python
for i in range(500):
print(2**i - 1)
`View the original notebook on nbviewer <http://nbviewer.jupyter.org/github/jupyter/notebook/blob/master/docs/source/examples/Notebook/Running%20Code.ipynb>`__
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