matplotlib · tacaswell · Feb 18, 2019 · Jan 24, 2019
diff --git a/doc/devel/contributing.rst b/doc/devel/contributing.rst
@@ -435,18 +435,22 @@ To include `logging` in your module, at the top of the module, you need to
 will log to a logger named ``matplotlib.yourmodulename``.
 
 If an end-user of Matplotlib sets up `logging` to display at levels
-more verbose than `logger.WARNING` in their code as follows::
+more verbose than `logger.WARNING` in their code with the Matplotlib-provided
+helper::
+
+  plt.set_loglevel("debug")
+
+or manually with ::
 
   import logging
-  fmt = '%(name)s:%(lineno)5d - %(levelname)s - %(message)s'
-  logging.basicConfig(level=logging.DEBUG, format=fmt)
+  logging.basicConfig(level=logging.DEBUG)
   import matplotlib.pyplot as plt
 
 Then they will receive messages like::
 
-  matplotlib.backends:   89 - INFO - backend MacOSX version unknown
-  matplotlib.yourmodulename: 347 - INFO - Here is some information
-  matplotlib.yourmodulename: 348 - DEBUG - Here is some more detailed information
+  DEBUG:matplotlib.backends:backend MacOSX version unknown
+  DEBUG:matplotlib.yourmodulename:Here is some information
+  DEBUG:matplotlib.yourmodulename:Here is some more detailed information
 
 Which logging level to use?
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~

diff --git a/doc/faq/troubleshooting_faq.rst b/doc/faq/troubleshooting_faq.rst
@@ -114,35 +114,18 @@ provide the following information in your e-mail to the `mailing list
   the error will help you find a bug in *your* code that is causing the
   problem.
 
-* You can get helpful debugging output from Matlotlib by using the `logging`
-  library in your code and posting the verbose output to the lists.  For a
-  command-line version of this, try::
+* Matplotlib provides debugging information through the `logging` library, and
+  a helper function to set the logging level: one can call ::
 
-     python -c "from logging import *; basicConfig(level=DEBUG); from pylab import *; plot(); show()"
+    plt.set_loglevel("info")  # or "debug" for more info
 
+  to obtain this debugging information.
 
-  If you want to put the debugging hooks in your own code, then the
-  most simple way to do so is to insert the following *before* any calls
-  to ``import matplotlib``::
-
-    import logging
-    logging.basicConfig(level=logging.DEBUG)
-
-    import matplotlib.pyplot as plt
-
-  Note that if you want to use `logging` in your own code, but do not
-  want verbose Matplotlib output, you can set the logging level
-  for Matplotlib independently::
-
-    import logging
-    # set DEBUG for everything
-    logging.basicConfig(level=logging.DEBUG)
-    logger = logging.getLogger('matplotlib')
-    # set WARNING for Matplotlib
-    logger.setLevel(logging.WARNING)
-
-  The `logging` module is very flexible, and can be a valuable tool in chasing
-  down errors.
+  Standard functions from the `logging` module are also applicable; e.g. one
+  could call ``logging.basicConfig(level="DEBUG")`` even before importing
+  Matplotlib (this is in particular necessary to get the logging info emitted
+  during Matplotlib's import), or attach a custom handler to the "matplotlib"
+  logger.  This may be useful if you use a custom logging configuration.
 
 If you compiled Matplotlib yourself, please also provide:
 

diff --git a/doc/users/next_whats_new/2019-01-24-AL-set_loglevel.rst b/doc/users/next_whats_new/2019-01-24-AL-set_loglevel.rst
@@ -0,0 +1,7 @@
+:orphan:
+
+New logging API
+```````````````
+
+`matplotlib.set_loglevel`/`.pyplot.set_loglevel` can be called to display more
+(or less) detailed logging output.
diff --git a/lib/matplotlib/__init__.py b/lib/matplotlib/__init__.py
@@ -206,48 +206,43 @@ def _check_versions():
     sys.argv = ['modpython']
 
 
-_verbose_msg = """\
-matplotlib.verbose is deprecated;
-Command line argument --verbose-LEVEL is deprecated.
-This functionality is now provided by the standard
-python logging library.  To get more (or less) logging output:
-    import logging
-    logger = logging.getLogger('matplotlib')
-    logger.set_level(logging.INFO)"""
+# The decorator ensures this always returns the same handler (and it is only
+# attached once).
+@functools.lru_cache()
+def _ensure_handler():
+    """
+    The first time this function is called, attach a `StreamHandler` using the
+    same format as `logging.basicConfig` to the Matplotlib root logger.
+
+    Return this handler every time this function is called.
+    """
+    handler = logging.StreamHandler()
+    handler.setFormatter(logging.Formatter(logging.BASIC_FORMAT))
+    _log.addHandler(handler)
+    return handler
 
 
-def _set_logger_verbose_level(level_str='silent', file_str='sys.stdout'):
+def set_loglevel(level):
     """
-    Use a --verbose-LEVEL level to set the logging level:
+    Sets the Matplotlib's root logger and root logger handler level, creating
+    the handler if it does not exist yet.
 
+    Typically, one should call ``set_loglevel("info")`` or
+    ``set_loglevel("debug")`` to get additional debugging information.
+
+    Parameters
+    ----------
+    level : {"notset", "debug", "info", "warning", "error", "critical"}
+        The log level of the handler.
+
+    Notes
+    -----
+    The first time this function is called, an additional handler is attached
+    to Matplotlib's root handler; this handler is reused every time and this
+    function simply manipulates the logger and handler's level.
     """
-    levelmap = {'silent': logging.WARNING, 'helpful': logging.INFO,
-                'debug': logging.DEBUG, 'debug-annoying': logging.DEBUG,
-                'info': logging.INFO, 'warning': logging.WARNING}
-    # Check that current state of logger isn't already more verbose
-    # than the requested level.  If it is more verbose, then leave more
-    # verbose.
-    newlev = levelmap[level_str]
-    oldlev = _log.getEffectiveLevel()
-    if newlev < oldlev:
-        _log.setLevel(newlev)
-        std = {
-            'sys.stdout': sys.stdout,
-            'sys.stderr': sys.stderr,
-        }
-        if file_str in std:
-            fileo = std[file_str]
-        else:
-            fileo = sys.stdout
-            try:
-                fileo = open(file_str, 'w')
-                # if this fails, we will just write to stdout
-            except IOError:
-                _log.warning('could not open log file "{0}" for writing. '
-                             'Check your matplotlibrc'.format(file_str))
-        console = logging.StreamHandler(fileo)
-        console.setLevel(newlev)
-        _log.addHandler(console)
+    _log.setLevel(level.upper())
+    _ensure_handler().setLevel(level.upper())
 
 
 def _logged_cached(fmt, func=None):

diff --git a/lib/matplotlib/pyplot.py b/lib/matplotlib/pyplot.py
@@ -18,6 +18,7 @@
 The object-oriented API is recommended for more complex plots.
 """
 
+import functools
 import importlib
 import inspect
 import logging
@@ -166,6 +167,11 @@ def uninstall_repl_displayhook():
 draw_all = _pylab_helpers.Gcf.draw_all
 
 
+@functools.wraps(matplotlib.set_loglevel)
+def set_loglevel(*args, **kwargs):  # Ensure this appears in the pyplot docs.
+    return matplotlib.set_loglevel(*args, **kwargs)
+
+
 @docstring.copy(Artist.findobj)
 def findobj(o=None, match=None, include_self=True):
     if o is None: