Weasyprint logging is missconfigured

[PamelaM]

From the python docs https://docs.python.org/2/howto/logging.html#library-config :

Note It is strongly advised that you do not add any handlers other than NullHandler to your 
library’s loggers. This is because the configuration of handlers is the prerogative of the 
application developer who uses your library. The application developer knows their target 
audience and what handlers are most appropriate for their application: if you add handlers 
‘under the hood’, you might well interfere with their ability to carry out unit tests and 
deliver logs which suit their requirements.

The default handler should be the NullHandler.

[liZe]

I agree. Silent logs have been asked before (at least #300 and #312) and that should be the default when WeasyPrint used as a library. We should log to stderr only when it's the "normal" way to handle logs, i.e. when WeasyPrint is launched from the CLI.

[PamelaM]

For those hitting this problem before it's fixed, here's how I've disabled the weasyprint logging handler - the logger needs to be set up before the first import of weasyprint

import logging

logger = logging.getLogger("weasyprint")
if not logger.handlers:
    logger.addHandler(logging.NullHandler())

from weasyprint import HTML

[hoIIer]

possibly related, I think all of the WARNING messages are coming from this package?

[alacret]

This hack doesn't work for Django applications. Neither in the settings.py nor before the import of the library.

Use this instead:

settings.py

import logging

...

logger = logging.getLogger("weasyprint")
logger.addHandler(logging.NullHandler())
logger.setLevel(40) # Only show errors, use 50

[conformist-mw]

For those who use Django internal LOGGING dict-like config:

LOGGING = {
    'version': 1,
    ...
    'handlers': {
        ...
        'null_handler': {
            'level': 'ERROR',
            'class': 'logging.NullHandler',
        },
    },
    'loggers': {
        ...
        'weasyprint': {
            'level': 'ERROR',
            'handlers': ['null_handler'],
        },
    }
}

[florianm]

Using

• weasyprint==59.0
• django_weasyprint==2.2.1
• django==4.2.5

I was still getting log messages such as __init__ glyf pruned.
The following logging config silences them:

LOGGING = {
    "version": 1,
    "disable_existing_loggers": False,
    "formatters": {
         ...
        "terse": {
            "format": "%(levelname)s %(asctime)s %(name)s %(message)s"
        },
    },
    "handlers": {
        "null_handler": {
            "level": "ERROR",
            "class": "logging.NullHandler",
        },
        "console": {
            "level": "DEBUG",
            "class": "logging.StreamHandler",
            "formatter": "terse",
        },
    },
    "loggers": {
       ...
        "fontTools.subset": {
            "level": "ERROR",
            "handlers": ["null_handler"],
        },
    },
}

Salient points:

• The offensively chatty logger's name is fontTools.subset, not weasyprint.
• I found the offending logger's name by including %(name)s in the formatter (formatter docs). The default %(module)s gave me only the filename __init__ which was not too useful.
• This setting completely silences the fonttools logger (null handler) AND only allows errors. YMMV - you could adjust the level to WARN and send to the console, so you get warnings like missing dependencies but silence the chatty info logs.