Python library: matplotlib

Installation

The following attempt to install matplotlib …

$ python3 -m pip install -U matplotlib

… resulted in these warnings:

WARNING: The scripts f2py, f2py3 and f2py3.9 are installed in '/home/rene/.local/bin' which is not on PATH.
Consider adding this directory to PATH or, if you prefer to suppress this warning, use --no-warn-script-location.
WARNING: The scripts fonttools, pyftmerge, pyftsubset and ttx are installed in '/home/rene/.local/bin' which is not on PATH.
Consider adding this directory to PATH or, if you prefer to suppress this warning, use --no-warn-script-location.

Plotting a simple graph

import numpy as np
import matplotlib.pyplot as plt

x = np.linspace(-np.pi, np.pi, 300)
y = np.sin(x)

plt.plot(x , y, 'r-', label='sin(x)') # r- draws a red line
plt.ylim(-1.25, 1.25)
plt.legend()
plt.show()

Github repository about-python, path: /libraries/matplotlib/sin.py

Matplotlib is currently using agg, which is a non-GUI backend, so cannot show the figure.

When I experienced this error on Debian, installing tkinter solved the problem.

Module members

`_add_data_doc()`
`_api`	Module
`atexit`	Module
`bezier`	Module
`cbook`	Module
`checkdep_usetex()`
`_check_versions()`
`_c_internal_utils`	Module
`_cm`	Module
`cm`	Module
`_cm_listed`	Module
`_color_data`	Module
`colormaps`	?
`colors`	Module
`color_sequences`	?
`contextlib`	Module
`cycler()`
`defaultParams`	`dict` object
`default_test_modules`	`list` object
`_deprecated_ignore_map`	`dict` object
`_deprecated_map`	`dict` object
`_deprecated_remain_as_none`	`dict` object
`_docstring`	Module
`_ensure_handler`	?
`_enums`	Module
`_ExecInfo`	`matplotlib._ExecInfo` class
`ExecutableNotFoundError`	`matplotlib.ExecutableNotFoundError` class
`_fontconfig_pattern`	Module
`ft2font`	Module
`functools`	Module
`get_backend()`
`get_cachedir()`
`get_configdir()`
`_get_config_or_cache_dir()`
`get_data_path()`
`_get_executable_info`	?
`_get_ssl_context`	?
`_get_version()`
`_get_xdg_cache_dir()`
`_get_xdg_config_dir()`
`importlib`	Module
`_init_tests()`
`inspect`	Module
`interactive()`
`is_interactive()`
`is_url()`
`_label_from_arg()`
`locale`	Module
`_log`	?
`_logged_cached()`
`logging`	Module
`MatplotlibDeprecationWarning`	`matplotlib._api.deprecation.MatplotlibDeprecationWarning` class
`matplotlib_fname()`
`MutableMapping`	?
`namedtuple()`
`numpy`	Module
`_open_file_or_url()`
`os`	Module
`Parameter`	`inspect.Parameter` class
`_parse_to_version_info()`
`parse_version()`
`Path`	`pathlib.Path` class
`_path`	Module
`path`	Module
`pprint`	Module
`_preprocess_data()`
`rc()`	A convenience function that allows to set multiple runtime configurations (=rc) at once. See also `rcParams`.
`rc_context()`	A context manager to override values of `rcParams` temporaily (`with mpl.rc_context({'lines.linewidth': 4}): …`). `rc_context` can also be used as a decorator to set rc defaults for a given function.
`rcdefaults()`
`rc_file()`
`rc_file_defaults()`
`RcParams`	?
`rcParams`	An instance of `matplotlib.RcParams` which is a dictionary like object used for run-time (=rc) configuration (for example `mpl.rcParams['lines.lineWidth'] = 3`). See also `rc()` and `rc_context` and the list of rcParams.
`rc_params()`
`rcParamsDefault`	?
`rc_params_from_file()`
`_rc_params_in_file()`
`rcParamsOrig`	?
`rcsetup`	Module
`re`	Module
`_replacer()`
`sanitize_sequence()`
`scale`	Module
`set_loglevel()`
`shutil`	Module
`subprocess`	Module
`sys`	Module
`tempfile`	Module
`test()`
`ticker`	Module
`transforms`	Module
`use()`	Configure the backend.
`validate_backend()`
`_version`	Module
`_VersionInfo`	`matplotlib._VersionInfo` class
`warnings`	Module

Using matplotlib in web servers

I've found this recommendation regarding useing matplotlib in Web servers

When using Matplotlib in a web server it is strongly recommended to not use pyplot (pyplot maintains references to the opened figures to make `~.matplotlib.pyplot.show` work, but this will cause memory leaks unless the figures are properly closed).
Since Matplotlib 3.1, one can directly create figures using the `.Figure` constructor and save them to in-memory buffers. In older versions, it was necessary to explicitly instantiate an Agg canvas (see e.g. :doc:`/gallery/user_interfaces/canvasagg`).

TODO

matplotlib.pyplot is a collection of functions that make matplotlib work like MATLAB.

Data to be plotted is expected to be provided as numpy.array or numpy.ma.masked_array objects, or objects that can be passed to numpy.asarray().

There are two interfaces:

Object oriented style (also refered to as explicit interface)
Implicit (modeled on MATLAB)

When using the OO style (?):

A matplotlib.figure.Figure object
A matplotlib.axes.Axes object represents a plot
A matplotlib.axis.Axis object represents one of the plot's axis (x, y or z)

Matplotlib accepts TeX equation expressions in any text expression.

Matplotlib uses the Pillow library to load image data.

Axes class

The Axes class is central to matplotlib because it defines the plotting area for data to be drawn.

Standard use

import matplotlib.pyplot as plt
import numpy             as np

#
#     Create a figure …
#
fig = plt.figure()

#
#     … use the figure to create one or more axes …
#
ax  = fig.add_subplot(2, 1, 1) # two rows, one column, first plot

#
#    … and use the axes to create the Artist primitives.
#

ax.…()

fig.show()
plt.waitforbuttonpress() # Really necessary?

Variant: create figure and axes in one go:

fig, ax = plt.subplots()

Coordinates

The default coordinate system for figures: 0,0 is bottom-left, 1,1 is top-right.

The coordinate system can be changed by setting the transform property of an Artist object.

See also the transFigure property of the Figure object.

styles/rcParams

Plots can be styled using rcParams. rcParams can be set using the following methods, in order of decreasing precedence:

Setting matplotlib.rcParams at runtime
Using style sheets
Using a matplotlibrc file

Available styles can be found with

print(plt.style.available)