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Code Cells

Code, Output, Streams

An empty code cell:

[ ]:

Two empty lines:

[ ]:

Leading/trailing empty lines:

[1]:


# 2 empty lines before, 1 after

A simple output:

[2]:
6 * 7
[2]:
42

The standard output stream:

[3]:
print('Hello, world!')
Hello, world!

Normal output + standard output

[4]:
print('Hello, world!')
6 * 7
Hello, world!
[4]:
42

The standard error stream is highlighted and displayed just below the code cell. The standard output stream comes afterwards (with no special highlighting). Finally, the “normal” output is displayed.

[5]:
import sys

print("I'll appear on the standard error stream", file=sys.stderr)
print("I'll appear on the standard output stream")
"I'm the 'normal' output"
I'll appear on the standard output stream
I'll appear on the standard error stream
[5]:
"I'm the 'normal' output"

Note

Using the IPython kernel, the order is actually mixed up, see https://github.com/ipython/ipykernel/issues/280.

Cell Magics

IPython can handle code in other languages by means of cell magics:

[6]:
%%bash
for i in 1 2 3
do
    echo $i
done
1
2
3

Special Display Formats

See IPython example notebook.

Local Image Files

[7]:
from IPython.display import Image
i = Image(filename='images/notebook_icon.png')
i
[7]:
_images/code-cells_20_0.png
[8]:
display(i)
_images/code-cells_21_0.png

See also SVG support for LaTeX.

[9]:
from IPython.display import SVG
SVG(filename='images/python_logo.svg')
[9]:
_images/code-cells_23_0.svg

Image URLs

[10]:
Image(url='https://www.python.org/static/img/python-logo-large.png')
[10]:
[11]:
Image(url='https://www.python.org/static/img/python-logo-large.png', embed=True)
---------------------------------------------------------------------------
gaierror                                  Traceback (most recent call last)
File /usr/lib/python3.10/urllib/request.py:1348, in AbstractHTTPHandler.do_open(self, http_class, req, **http_conn_args)
   1347 try:
-> 1348     h.request(req.get_method(), req.selector, req.data, headers,
   1349               encode_chunked=req.has_header('Transfer-encoding'))
   1350 except OSError as err: # timeout error

File /usr/lib/python3.10/http/client.py:1282, in HTTPConnection.request(self, method, url, body, headers, encode_chunked)
   1281 """Send a complete request to the server."""
-> 1282 self._send_request(method, url, body, headers, encode_chunked)

File /usr/lib/python3.10/http/client.py:1328, in HTTPConnection._send_request(self, method, url, body, headers, encode_chunked)
   1327     body = _encode(body, 'body')
-> 1328 self.endheaders(body, encode_chunked=encode_chunked)

File /usr/lib/python3.10/http/client.py:1277, in HTTPConnection.endheaders(self, message_body, encode_chunked)
   1276     raise CannotSendHeader()
-> 1277 self._send_output(message_body, encode_chunked=encode_chunked)

File /usr/lib/python3.10/http/client.py:1037, in HTTPConnection._send_output(self, message_body, encode_chunked)
   1036 del self._buffer[:]
-> 1037 self.send(msg)
   1039 if message_body is not None:
   1040
   1041     # create a consistent interface to message_body

File /usr/lib/python3.10/http/client.py:975, in HTTPConnection.send(self, data)
    974 if self.auto_open:
--> 975     self.connect()
    976 else:

File /usr/lib/python3.10/http/client.py:1447, in HTTPSConnection.connect(self)
   1445 "Connect to a host on a given (SSL) port."
-> 1447 super().connect()
   1449 if self._tunnel_host:

File /usr/lib/python3.10/http/client.py:941, in HTTPConnection.connect(self)
    940 sys.audit("http.client.connect", self, self.host, self.port)
--> 941 self.sock = self._create_connection(
    942     (self.host,self.port), self.timeout, self.source_address)
    943 # Might fail in OSs that don't implement TCP_NODELAY

File /usr/lib/python3.10/socket.py:824, in create_connection(address, timeout, source_address)
    823 err = None
--> 824 for res in getaddrinfo(host, port, 0, SOCK_STREAM):
    825     af, socktype, proto, canonname, sa = res

File /usr/lib/python3.10/socket.py:955, in getaddrinfo(host, port, family, type, proto, flags)
    954 addrlist = []
--> 955 for res in _socket.getaddrinfo(host, port, family, type, proto, flags):
    956     af, socktype, proto, canonname, sa = res

gaierror: [Errno -2] Name or service not known

During handling of the above exception, another exception occurred:

URLError                                  Traceback (most recent call last)
Cell In [11], line 1
----> 1 Image(url='https://www.python.org/static/img/python-logo-large.png', embed=True)

File /usr/lib/python3/dist-packages/IPython/core/display.py:957, in Image.__init__(self, data, url, filename, format, embed, width, height, retina, unconfined, metadata, alt)
    955 self.unconfined = unconfined
    956 self.alt = alt
--> 957 super(Image, self).__init__(data=data, url=url, filename=filename,
    958         metadata=metadata)
    960 if self.width is None and self.metadata.get('width', {}):
    961     self.width = metadata['width']

File /usr/lib/python3/dist-packages/IPython/core/display.py:327, in DisplayObject.__init__(self, data, url, filename, metadata)
    324 elif self.metadata is None:
    325     self.metadata = {}
--> 327 self.reload()
    328 self._check_data()

File /usr/lib/python3/dist-packages/IPython/core/display.py:992, in Image.reload(self)
    990 """Reload the raw data from file or URL."""
    991 if self.embed:
--> 992     super(Image,self).reload()
    993     if self.retina:
    994         self._retina_shape()

File /usr/lib/python3/dist-packages/IPython/core/display.py:358, in DisplayObject.reload(self)
    355 elif self.url is not None:
    356     # Deferred import
    357     from urllib.request import urlopen
--> 358     response = urlopen(self.url)
    359     data = response.read()
    360     # extract encoding from header, if there is one:

File /usr/lib/python3.10/urllib/request.py:216, in urlopen(url, data, timeout, cafile, capath, cadefault, context)
    214 else:
    215     opener = _opener
--> 216 return opener.open(url, data, timeout)

File /usr/lib/python3.10/urllib/request.py:519, in OpenerDirector.open(self, fullurl, data, timeout)
    516     req = meth(req)
    518 sys.audit('urllib.Request', req.full_url, req.data, req.headers, req.get_method())
--> 519 response = self._open(req, data)
    521 # post-process response
    522 meth_name = protocol+"_response"

File /usr/lib/python3.10/urllib/request.py:536, in OpenerDirector._open(self, req, data)
    533     return result
    535 protocol = req.type
--> 536 result = self._call_chain(self.handle_open, protocol, protocol +
    537                           '_open', req)
    538 if result:
    539     return result

File /usr/lib/python3.10/urllib/request.py:496, in OpenerDirector._call_chain(self, chain, kind, meth_name, *args)
    494 for handler in handlers:
    495     func = getattr(handler, meth_name)
--> 496     result = func(*args)
    497     if result is not None:
    498         return result

File /usr/lib/python3.10/urllib/request.py:1391, in HTTPSHandler.https_open(self, req)
   1390 def https_open(self, req):
-> 1391     return self.do_open(http.client.HTTPSConnection, req,
   1392         context=self._context, check_hostname=self._check_hostname)

File /usr/lib/python3.10/urllib/request.py:1351, in AbstractHTTPHandler.do_open(self, http_class, req, **http_conn_args)
   1348         h.request(req.get_method(), req.selector, req.data, headers,
   1349                   encode_chunked=req.has_header('Transfer-encoding'))
   1350     except OSError as err: # timeout error
-> 1351         raise URLError(err)
   1352     r = h.getresponse()
   1353 except:

URLError: <urlopen error [Errno -2] Name or service not known>
[12]:
Image(url='https://jupyter.org/assets/homepage/main-logo.svg')
[12]:

Math

[13]:
from IPython.display import Math
eq = Math(r'\int\limits_{-\infty}^\infty f(x) \delta(x - x_0) dx = f(x_0)')
eq
[13]:
$\displaystyle \int\limits_{-\infty}^\infty f(x) \delta(x - x_0) dx = f(x_0)$
[14]:
display(eq)
$\displaystyle \int\limits_{-\infty}^\infty f(x) \delta(x - x_0) dx = f(x_0)$
[15]:
from IPython.display import Latex
Latex(r'This is a \LaTeX{} equation: $a^2 + b^2 = c^2$')
[15]:
This is a \LaTeX{} equation: $a^2 + b^2 = c^2$
[16]:
%%latex
\begin{equation}
\int\limits_{-\infty}^\infty f(x) \delta(x - x_0) dx = f(x_0)
\end{equation}
\begin{equation} \int\limits_{-\infty}^\infty f(x) \delta(x - x_0) dx = f(x_0) \end{equation}

Plots

Make sure to use at least version 0.1.6 of the matplotlib-inline package (which is an automatic dependency of the ipython package).

By default, the plots created with the “inline” backend have the wrong size. More specifically, PNG plots (the default) will be slightly larger than SVG and PDF plots.

This can be fixed easily by creating a file named matplotlibrc (in the directory where your Jupyter notebooks live, e.g. in this directory: matplotlibrc) and adding the following line:

figure.dpi: 96

If you are using Git to manage your files, don’t forget to commit this local configuration file to your repository. Different directories can have different local configurations. If a given configuration should apply to multiple directories, symbolic links can be created in each directory.

For more details, see Default Values for Matplotlib’s “inline” Backend.

By default, plots are generated in the PNG format. In most cases, it looks better if SVG plots are used for HTML output and PDF plots are used for LaTeX/PDF. This can be achieved by setting nbsphinx_execute_arguments in your conf.py file like this:

nbsphinx_execute_arguments = [
    "--InlineBackend.figure_formats={'svg', 'pdf'}",
]

In the following example, nbsphinx should use an SVG image in the HTML output and a PDF image for LaTeX/PDF output (other Jupyter clients like JupyterLab will still show the default PNG format).

[17]:
import matplotlib.pyplot as plt
[18]:
fig, ax = plt.subplots(figsize=[6, 3])
ax.plot([4, 9, 7, 20, 6, 33, 13, 23, 16, 62, 8]);
_images/code-cells_38_0.svg

For comparison, this is how it would look in PNG format …

[19]:
%config InlineBackend.figure_formats = ['png']
[20]:
fig
[20]:
_images/code-cells_41_0.png

… and in 'png2x' (a.k.a. 'retina') format:

[21]:
%config InlineBackend.figure_formats = ['png2x']
[22]:
fig
[22]:
_images/code-cells_44_0.png

Pandas Dataframes

Pandas dataframes should be displayed as nicely formatted HTML tables (if you are using HTML output).

[23]:
import numpy as np
import pandas as pd
[24]:
df = pd.DataFrame(np.random.randint(0, 100, size=[5, 4]),
                  columns=['a', 'b', 'c', 'd'])
df
[24]:
a b c d
0 68 59 94 53
1 57 73 43 52
2 30 5 11 72
3 40 32 96 88
4 74 67 66 36

For LaTeX output, however, the plain text output is used by default.

To get nice LaTeX tables, a few settings have to be changed:

[25]:
pd.set_option('display.latex.repr', True)

This is not enabled by default because of Pandas issue #12182.

The generated LaTeX tables utilize the booktabs package, so you have to make sure that package is loaded in the preamble with:

\usepackage{booktabs}

In order to allow page breaks within tables, you should use:

[26]:
pd.set_option('display.latex.longtable', True)

The longtable package is already used by Sphinx, so you don’t have to manually load it in the preamble.

Finally, if you want to use LaTeX math expressions in your dataframe, you’ll have to disable escaping:

[27]:
pd.set_option('display.latex.escape', False)

The above settings should have no influence on the HTML output, but the LaTeX output should now look nicer:

[28]:
df = pd.DataFrame(np.random.randint(0, 100, size=[10, 4]),
                  columns=[r'$\alpha$', r'$\beta$', r'$\gamma$', r'$\delta$'])
df
[28]:
$\alpha$ $\beta$ $\gamma$ $\delta$
0 31 35 96 73
1 30 58 56 16
2 70 18 11 38
3 13 93 24 96
4 68 47 57 86
5 74 80 59 64
6 55 41 72 59
7 51 7 77 84
8 28 74 88 7
9 41 56 91 16

Markdown Content

[29]:
from IPython.display import Markdown
[30]:
md = Markdown("""
# Markdown

It *should* show up as **formatted** text
with things like [links] and images.

[links]: https://jupyter.org/

![Jupyter notebook icon](images/notebook_icon.png)

## Markdown Extensions

There might also be mathematical equations like
$a^2 + b^2 = c^2$
and even tables:

A     | B     | A and B
------|-------|--------
False | False | False
True  | False | False
False | True  | False
True  | True  | True

""")
md
[30]:

Markdown

It should show up as formatted text with things like links and images.

Jupyter notebook icon
Markdown Extensions

There might also be mathematical equations like \(a^2 + b^2 = c^2\) and even tables:

A

B

A and B

False

False

False

True

False

False

False

True

False

True

True

True

YouTube Videos

[31]:
from IPython.display import YouTubeVideo
YouTubeVideo('9_OIs49m56E')
[31]:

Interactive Widgets (HTML only)

The basic widget infrastructure is provided by the ipywidgets module. More advanced widgets are available in separate packages, see for example https://jupyter.org/widgets.

The JavaScript code which is needed to display Jupyter widgets is loaded automatically (using RequireJS). If you want to use non-default URLs or local files, you can use the nbsphinx_widgets_path and nbsphinx_requirejs_path settings.

Other Languages

The examples shown here are using Python, but the widget technology can also be used with different Jupyter kernels (i.e. with different programming languages).

Troubleshooting

To obtain more information if widgets are not displayed as expected, you will need to look at the error message in the web browser console.

To figure out how to open the web browser console, you may look at the web browser documentation:

The error is most probably linked to the JavaScript files not being loaded or loaded in the wrong order within the HTML file. To analyze the error, you can inspect the HTML file within the web browser (e.g.: right-click on the page and select View Page Source) and look at the <head> section of the page. That section should contain some JavaScript libraries. Those relevant for widgets are:

<!-- require.js is a mandatory dependency for jupyter-widgets -->
<script crossorigin="anonymous" integrity="sha256-Ae2Vz/4ePdIu6ZyI/5ZGsYnb+m0JlOmKPjt6XZ9JJkA=" src="https://cdnjs.cloudflare.com/ajax/libs/require.js/2.3.4/require.min.js"></script>
<!-- jupyter-widgets JavaScript -->
<script type="text/javascript" src="https://unpkg.com/@jupyter-widgets/html-manager@^0.18.0/dist/embed-amd.js"></script>
<!-- JavaScript containing custom Jupyter widgets -->
<script src="../_static/embed-widgets.js"></script>

The two first elements are mandatory. The third one is required only if you designed your own widgets but did not publish them on npm.js.

If those libraries appear in a different order, the widgets won’t be displayed.

Here is a list of possible solutions:

  • If the widgets are not displayed, see #519.

  • If the widgets are displayed multiple times, see #378.

Arbitrary JavaScript Output (HTML only)

[32]:
%%javascript

var text = document.createTextNode("Hello, I was generated with JavaScript!");
// Content appended to "element" will be visible in the output area:
element.appendChild(text);

Unsupported Output Types

If a code cell produces data with an unsupported MIME type, the Jupyter Notebook doesn’t generate any output. nbsphinx, however, shows a warning message.

[33]:
display({
    'text/x-python': 'print("Hello, world!")',
    'text/x-haskell': 'main = putStrLn "Hello, world!"',
}, raw=True)

Data type cannot be displayed: text/x-python, text/x-haskell

ANSI Colors

The standard output and standard error streams may contain ANSI escape sequences to change the text and background colors.

[34]:
print('BEWARE: \x1b[1;33;41mugly colors\x1b[m!', file=sys.stderr)
print('AB\x1b[43mCD\x1b[35mEF\x1b[1mGH\x1b[4mIJ\x1b[7m'
      'KL\x1b[49mMN\x1b[39mOP\x1b[22mQR\x1b[24mST\x1b[27mUV')
ABCDEFGHIJKLMNOPQRSTUV
BEWARE: ugly colors!

The following code showing the 8 basic ANSI colors is based on https://tldp.org/HOWTO/Bash-Prompt-HOWTO/x329.html. Each of the 8 colors has an “intense” variation, which is used for bold text.

[35]:
text = ' XYZ '
formatstring = '\x1b[{}m' + text + '\x1b[m'

print(' ' * 6 + ' ' * len(text) +
      ''.join('{:^{}}'.format(bg, len(text)) for bg in range(40, 48)))
for fg in range(30, 38):
    for bold in False, True:
        fg_code = ('1;' if bold else '') + str(fg)
        print(' {:>4} '.format(fg_code) + formatstring.format(fg_code) +
              ''.join(formatstring.format(fg_code + ';' + str(bg))
                      for bg in range(40, 48)))
            40   41   42   43   44   45   46   47
   30  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ 
 1;30  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ 
   31  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ 
 1;31  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ 
   32  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ 
 1;32  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ 
   33  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ 
 1;33  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ 
   34  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ 
 1;34  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ 
   35  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ 
 1;35  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ 
   36  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ 
 1;36  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ 
   37  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ 
 1;37  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ  XYZ 

ANSI also supports a set of 256 indexed colors. The following code showing all of them is based on http://bitmote.com/index.php?post/2012/11/19/Using-ANSI-Color-Codes-to-Colorize-Your-Bash-Prompt-on-Linux.

[36]:
formatstring = '\x1b[38;5;{0};48;5;{0}mX\x1b[1mX\x1b[m'

print('  + ' + ''.join('{:2}'.format(i) for i in range(36)))
print('  0 ' + ''.join(formatstring.format(i) for i in range(16)))
for i in range(7):
    i = i * 36 + 16
    print('{:3} '.format(i) + ''.join(formatstring.format(i + j)
                                      for j in range(36) if i + j < 256))
  +  0 1 2 3 4 5 6 7 8 91011121314151617181920212223242526272829303132333435
  0 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 16 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 52 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 88 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
124 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
160 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
196 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
232 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

You can even use 24-bit RGB colors:

[37]:
start = 255, 0, 0
end = 0, 0, 255
length = 79
out = []

for i in range(length):
    rgb = [start[c] + int(i * (end[c] - start[c]) / length) for c in range(3)]
    out.append('\x1b['
               '38;2;{rgb[2]};{rgb[1]};{rgb[0]};'
               '48;2;{rgb[0]};{rgb[1]};{rgb[2]}mX\x1b[m'.format(rgb=rgb))
print(''.join(out))
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX