Python：在其他输出之前记录打印到控制台的注释

Question

I have been trying to understand logging in python. I have an init module, two other modules and a main module. For some reason, when I run my module, log details jump the code flow and are printed first before the other outputs

Could someone tell me why this is happening

this is in __init__.py

from dir1.mod1 import FirstClass
from dir1.mod2 import SecondClass

logger = logging.getLogger(__name__)

logger.setLevel(logging.DEBUG)
f_handler=logging.FileHandler('python_logs.log')
f_handler.setLevel(logging.DEBUG)
c_handler = logging.StreamHandler()
c_handler.setLevel(logging.ERROR)

f_formatter = logging.Formatter('%(name)s - %(levelname)s - %(message)s')
c_formatter = logging.Formatter('%(name)s - %(levelname)s - %(message)s')

f_handler.setFormatter(f_formatter)
c_handler.setFormatter(c_formatter)

logger.addHandler(f_handler)
logger.addHandler(c_handler)

This is in other two modules(written inside __init__() of the resp class

self.logger = logging.getLogger(__name__)

snippet of addn() function defined inside one of the module

def addn(self):
    z=self.x +self.y
    print('sum is '+z)
    self.logger.error('incrementing number!')
    self.logger.info('Still incrementing number!!')
    return z

And my main modules(which I run) has this:

from dir1.mod1 import FirstClass
from dir1.mod2 import SecondClass

number = FirstClass(2,2)
print('addition results')
number.addn()

I was expecting a output as below

addition results

sum is 3

dir1.mod1 - ERROR - incrementing number!

But what I got was

dir1.mod1 - ERROR - incrementing number!

dir1.mod1 - ERROR - incrementing number!

addition results:

sum is 3

Why is the log message printed first jumping out of code flow? And also could someone tell me why log message gets printed twice??

Answer 1

U can try disable the propagate property of your logger.

Propagate : If this attribute evaluates to true, events logged to this logger will be passed to the handlers of higher level (ancestor) loggers, in addition to any handlers attached to this logger. Messages are passed directly to the ancestor loggers' handlers - neither the level nor filters of the ancestor loggers in question are considered.

This is an example of init logger that uses file and stdout with different debug level:

def init_logger_singleton():

    global logger

    logger = logging.getLogger(name='loggerName')
    logger.propagate = False
    logger.setLevel(10)
    formatter = logging.Formatter(
        '\t%(message)s'
    )

    filehandler = logging.StreamHandler()
    filehandler.setLevel(40)
    filehandler.setFormatter(formatter)
    logger.addHandler(filehandler)

I used number to define the log level, but 10 = DEBUG and 40 = ERRO. More information at this link.

Answer 2

Python StreamHandler will log to stderr by default while you print statements goes to stdout. Those are two different pipelines and the ordering isn't guaranteed between them.

To ensure proper ordering start by sending all output to the same pipe. For example you could add the file=sys.stderr argument to your print statements.

Answer 3

您还可以将参数sys.stdout添加到您的流处理程序，因此print和记录器事件都将传递到一个通道。

stream_handler = logging.StreamHandler(sys.stdout)