[Bug]: matplotlib.set_loglevel() adds a console handler #23646
Description
Bug summary
matplotlib.set_loglevel() adds a logging console handler which then leads to duplicate messages in application code. The best practice is to allow the application code to add the handlers to its logger along with formatting, filtering, etc. The existing #13264 attempted to address this.
Code for reproduction
import logging
import matplotlib as mpl
mpl_logger = logging.getLogger("matplotlib")
mpl.set_loglevel("debug")
mpl_logger.hasHandlers()
logger = logging.getLogger()
ch = logging.StreamHandler()
logger.addHandler(ch)
logger.setLevel(logging.DEBUG)
import matplotlib.pyplot as pltActual outcome
True
DEBUG:matplotlib:CACHEDIR=C:\Users\ljohnsto.matplotlib
CACHEDIR=C:\Users\ljohnsto.matplotlib
DEBUG:matplotlib.font_manager:Using fontManager instance from C:\Users\ljohnsto.matplotlib\fontlist-v330.json
Using fontManager instance from C:\Users\ljohnsto.matplotlib\fontlist-v330.json
Expected outcome
False
CACHEDIR=C:\Users\ljohnsto.matplotlib
Using fontManager instance from C:\Users\ljohnsto.matplotlib\fontlist-v330.json
Additional information
The workaround is:
In [1]: import logging
In [2]: import matplotlib as mpl
In [3]: mpl_logger = logging.getLogger("matplotlib")
In [4]: mpl.set_loglevel("debug")
In [5]: mpl_logger_handlers = mpl_logger.handlers.copy()
In [6]: for h in mpl_logger_handlers:
...: mpl_logger.removeHandler(h)
...:
In [7]: logger = logging.getLogger()
In [8]: ch = logging.StreamHandler()
In [9]: logger.addHandler(ch)
In [10]: logger.setLevel(logging.DEBUG)
In [11]: import matplotlib.pyplot as plt
CACHEDIR=C:\Users\ljohnsto\.matplotlib
Using fontManager instance from C:\Users\ljohnsto\.matplotlib\fontlist-v330.json
'''
### Operating system
Windows
### Matplotlib Version
3.5.2
### Matplotlib Backend
TkAgg
### Python version
3.9.13
### Jupyter version
_No response_
### Installation
pip