Move pylab documentation to its own module page

Previously, pylab was not listed under modules, but the module docstring
(and thus also the target of pylab links) wa on the API Reference top
page.

While pylab is discouraged, it's still a regular module and should be
handled as such. Even more importantly, by removing the pylab section
from the API reference top page, we de-emphasize it. Note, that pylab is
still mentioned in the more in-depth backend discussion at
https://matplotlib.org/devdocs/users/explain/figure/api_interfaces.html

Co-authored-by: hannah <[email protected]>
Co-authored-by: Jody Klymak <[email protected]>

Author: 3 people

doc/api/index.rst

@@ -80,12 +80,6 @@ Further reading:
 
 .. _api-index:
 
-The pylab API (discouraged)
-^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-.. automodule:: pylab
-   :no-members:
-
 Modules
 -------
 
@@ -162,3 +156,4 @@ Alphabetical list of modules:
    toolkits/mplot3d.rst
    toolkits/axes_grid1.rst
    toolkits/axisartist.rst
+   pylab.rst

doc/api/pylab.rst

@@ -0,0 +1,6 @@
+*********
+``pylab``
+*********
+
+.. automodule:: pylab
+   :no-members:

lib/matplotlib/pylab.py

@@ -1,14 +1,24 @@
 """
+`pylab` is a historic interface and its use is strongly discouraged. The equivalent
+replacement is `matplotlib.pyplot`.  See :ref:` api_interfaces` for a full overview
+of Matplotlib interfaces.
+
+`pylab` was designed to support a MATLAB-like way of working with all plotting related
+functions directly available in the global namespace. This was achieved through a
+wildcard import (``from pylab import *``).
+
 .. warning::
-   Since heavily importing into the global namespace may result in unexpected
-   behavior, the use of pylab is strongly discouraged. Use `matplotlib.pyplot`
-   instead.
-
-`pylab` is a module that includes `matplotlib.pyplot`, `numpy`, `numpy.fft`,
-`numpy.linalg`, `numpy.random`, and some additional functions, all within
-a single namespace. Its original purpose was to mimic a MATLAB-like way
-of working by importing all functions into the global namespace. This is
-considered bad style nowadays.
+   The use of `pylab` is discouraged for the following reasons:
+
+   ``from pylab import *`` imports all the functions from `matplotlib.pyplot`, `numpy`,
+   `numpy.fft`, `numpy.linalg`, and `numpy.random`, and some additional functions into
+   the global namespace.
+
+   Such a pattern is nowadays considered bad practice, as it clutters the global
+   namespace. Even more severely, in the case of `pylab`, this will overwrite some
+   builtin functions (e.g. the builtin `sum` will be replaced by `numpy.sum`), which
+   can lead to unexpected behavior.
+
 """
 
 from matplotlib.cbook import flatten, silent_list