Capturing output representations¶

This example demonstrates how the configuration capture_repr (Controlling what output is captured) works. The default capture_repr setting is capture_repr: ('_repr_html_', '__repr__') and was used when building the Sphinx-Gallery documentation. The output that is captured with this setting is demonstrated in this example. Differences in outputs that would be captured with other capture_repr settings is also explained.

Nothing is captured for the code block below because no data is directed to standard output and the last statement is an assignment, not an expression.

# example 1
a = 2
b = 10

If you did wish to capture the value of b, you would need to use:

# example 2
a = 2
b = 10
b   # this is an expression

Out:

10

Sphinx-Gallery first attempts to capture the _repr_html_ of b as this is the first ‘representation’ method in the capture_repr tuple. As this method does not exist for b, Sphinx-Gallery moves on and tries to capture the __repr__ method, which is second in the tuple. This does exist for b so it is captured and the output is seen above.

A pandas dataframe is used in the code block below to provide an example of an expression with a _repr_html_ method.

# example 3
import pandas as pd

df = pd.DataFrame(data = {'col1': [1, 2], 'col2': [3, 4]})
df
col1 col2
0 1 3
1 2 4


The pandas dataframe df has both a __repr__ and _repr_html_ method. As _repr_html_ appears first in the capture_repr tuple, the _repr_html_ is captured in preference to __repr__.

For the example below, there is data directed to standard output and the last statement is an expression.

# example 4
print('Hello world')
a + b

Out:

Hello world

12

print() outputs to standard output, which is always captured. The string 'Hello world' is thus captured. A ‘representation’ of the last expression is also captured. Again, since this expression a + b does not have a _repr_html_ method, the __repr__ method is captured.

Matplotlib output¶

Matplotlib function calls generally return a Matplotlib object as well as outputting the figure. For code blocks where the last statement is a Matplotlib expression, a ‘representation’ of the object will be captured, as well as the plot. This is because Matplotlib objects have a __repr__ method and our capture_repr tuple contains __repr__. Note that Matplotlib objects also have a __str__ method.

In the example below, matplotlib.pyplot.plot() returns a list of Line2D objects representing the plotted data and the __repr__ of the list is captured as well as the figure:

import matplotlib.pyplot as plt

plt.plot([1,2,3])
plot 3 capture repr

Out:

[<matplotlib.lines.Line2D object at 0x7f1dc86fb990>]

To avoid capturing the text representation, you can assign the last Matplotlib expression to a temporary variable:

_ = plt.plot([1,2,3])
plot 3 capture repr

Alternatively, you can add plt.show(), which does not return anything, to the end of the code block:

plt.plot([1,2,3])
plt.show()
plot 3 capture repr

The capture_repr configuration¶

The capture_repr configuration is ('_repr_html_', '__repr__') by default. This directs Sphinx-Gallery to capture ‘representations’ of the last statement of a code block, if it is an expression. Sphinx-Gallery does this according to the order ‘representations’ appear in the tuple. With the default capture_repr setting, _repr_html_ is attempted to be captured first. If this method does not exist, the __repr__ method would be captured. If the __repr__ also does not exist (unlikely for non-user defined objects), nothing would be captured. For example, if the the configuration was set to 'capture_repr': ('_repr_html_') nothing would be captured for example 2 as b does not have a _repr_html_. You can change the ‘representations’ in the capture_repr tuple to finely tune what is captured in your example .py files.

To only capture data directed to standard output you can set capture_repr to be an empty tuple: capture_repr: (). With this setting, only data directed to standard output is captured. For the examples above, output would only be captured for example 4. Although the last statement is an expression for examples 2, 3 and 4 no ‘representation’ of the last expression would be output. You would need to add print() to the last expression to capture a ‘representation’ of it. The empty tuple setting imitates the behaviour of Sphinx-Gallery prior to v0.5.0, when this configuration was introduced.

Total running time of the script: ( 0 minutes 2.782 seconds)

Estimated memory usage: 8 MB

Gallery generated by Sphinx-Gallery