StreamHandler()<\/code> \u2013 controls what is printed to the console<\/li>\nFileHandler()<\/code> \u2013 controls what is printed to the log file<\/li>\n<\/ul>\nWhenever you start your script, you will need to access this function to initialize the handlers. For example, in main():<\/p>\n
global logger\nlogger = log_handlers(logging.INFO, logging.INFO)<\/pre>\nBefore your script ends, you should shut the logging module down. For example, I used this as the last line of code in main():<\/p>\n
logging.shutdown()<\/pre>\nIn order to use the logger created previously, you will need to use the following code in place of a print statement. Where you would previously print a string to the console like this:<\/p>\n
# print a raw string\nprint \"Print this string...\"<\/pre>\nYou can now print the same string to the console AND the log file by using logger.info()<\/code> with the string in parenthesis, like this:<\/p>\n# print a raw string to both the console and the log\nlogger.info('Print this string...')<\/pre>\nWhere you would previously print a string and variable to the console like this:<\/p>\n
# print a raw string and variable containing a string\nprint \"The year is\", year\n<\/pre>\nYou can now print the same string and variable to the console AND the log file using logger.info like this:<\/p>\n
logger.info(\"The year is: %s\" % (year))<\/pre>\nNotice that the variable name year is in its own parenthesis. The string value stored in the variable will be substituted into the %s<\/code> in the double quotes. This will yield the same results as the print statement.<\/p>\nWhere you would previously print three variables, containing a string, number, and list like this:<\/p>\n
# print three variables, containing a string, number, and list\nprint year, xldate, pvid_list<\/pre>\nYou can now print the same three variables to the console AND the log file using logger.info<\/code> like this:<\/p>\nlogger.info(\"%s %s %s\" % (year, xldate, pvid_list))<\/pre>\nNotice that all three variable names are in the parenthesis, separated by commas. Each of these point to their own %s<\/code> placeholder in the string portion (in order). The first variable points to the first %s<\/code>, the second variable points to the second %s, etc..<\/p>\n![\"\"](\"http:\/\/bluegalaxy.info\/codewalk\/wp-content\/uploads\/2018\/07\/three-subs.png\")
<\/p>\n
The output is the same as the print statement:<\/p>\n
2015 41000 ['19615056', '15612770', '15612771']<\/pre>\nAll three lines also went to the log file, in this case called \u201cOutput_log_020615_1129.txt\u201d:<\/p>\n
![\"\"](\"http:\/\/bluegalaxy.info\/codewalk\/wp-content\/uploads\/2018\/07\/logging-out.png\")
<\/p>\n
The log file can be named anything you like. It can have the extension .txt<\/code> or .log<\/code>. In this example case, I used today\u2019s date and timestamp as part of the name of the log. \u201cOutput_log_\u201d + MMDDYY + \u201c_\u201d + HHMM + \u201c.txt\u201d.<\/p>\nHere is the log_handlers function that makes this work:<\/p>\n
def log_handlers(file_level, console_level = None):\n function_name = inspect.stack()[1][3]\n logger = logging.getLogger(function_name)\n logger.setLevel(logging.DEBUG) #By default, DEBUG logs all messages\n\n #log_name = 'Output_log_' + getDate() + '.log'\n log_name = 'Output_log_' + getDate() + '_' + getTime() + '.txt'\n\n # Clear out existing handlers to avoid duplicated data\n logger.handlers = []\n\n if not logger.handlers:\n if console_level != None:\n ch = logging.StreamHandler() #StreamHandler logs to console\n ch.setLevel(console_level)\n ch_format = logging.Formatter('%(message)s')\n ch.setFormatter(ch_format)\n logger.addHandler(ch)\n\n #FileHandler logs to log file. mode='w' is optional for overwrite\n fh = logging.FileHandler(log_name.format(function_name), mode='w')\n fh.setLevel(file_level)\n fh_format = logging.Formatter('%(message)s')\n fh.setFormatter(fh_format)\n logger.addHandler(fh)\n\n return logger<\/pre>\nThe mode=\u2018w\u2019<\/code> in the Filehandler setup is optional and will cause the log handler to overwrite the existing log file with each subsequent execution of your script. This can be left off and the default setting would be \u201cappend\u201d.<\/p>\nfh = logging.FileHandler(log_name.format(function_name), mode='w')<\/pre>\nFor example:<\/p>\n
fh = logging.FileHandler(log_name.format(function_name))<\/pre>\nWhile this tutorial covers just a single use case, there are many other things that can be done with the logging module. For more details, visit the following website resources:
\nhttps:\/\/docs.python.org\/2\/library\/logging.html<\/a>
\nhttp:\/\/www.blog.pythonlibrary.org\/2012\/08\/02\/python-101-an-intro-to-logging<\/a><\/p>\nComplete Python code for this tutorial can be found on my github here:
\nhttps:\/\/github.com\/chris-relaxing\/python-how-to-use-logging<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"Sending print statements to the console is very common in Python coding. It is simply a matter of using the key word print, followed by what you want printed to the screen. For example: # variables year = ‘2015’ xldate = 41000 pvid_list = [“19615056”, “15612770”, “15612771”] # print a raw string print “Print this … Continue reading Python: How to use the logging module<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[22],"tags":[4],"class_list":["post-2092","post","type-post","status-publish","format-standard","hentry","category-python-language","tag-python"],"_links":{"self":[{"href":"https:\/\/bluegalaxy.info\/codewalk\/wp-json\/wp\/v2\/posts\/2092","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/bluegalaxy.info\/codewalk\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/bluegalaxy.info\/codewalk\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/bluegalaxy.info\/codewalk\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/bluegalaxy.info\/codewalk\/wp-json\/wp\/v2\/comments?post=2092"}],"version-history":[{"count":9,"href":"https:\/\/bluegalaxy.info\/codewalk\/wp-json\/wp\/v2\/posts\/2092\/revisions"}],"predecessor-version":[{"id":2880,"href":"https:\/\/bluegalaxy.info\/codewalk\/wp-json\/wp\/v2\/posts\/2092\/revisions\/2880"}],"wp:attachment":[{"href":"https:\/\/bluegalaxy.info\/codewalk\/wp-json\/wp\/v2\/media?parent=2092"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/bluegalaxy.info\/codewalk\/wp-json\/wp\/v2\/categories?post=2092"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/bluegalaxy.info\/codewalk\/wp-json\/wp\/v2\/tags?post=2092"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}