FileHandler
- Python course
- Advanced
- Lesson 70/83
- 5 min
Learn to write to a file with FileHandler.
FileHandler
logging.FileHandler writes logs to a file. The filename parameter takes a file path; it is added to the logger with addHandler.
import logging
handler = logging.FileHandler("app.log")
handler.setFormatter(logging.Formatter("%(levelname)s:%(message)s"))
logger = logging.getLogger("myapp")
logger.addHandler(handler)
logger.setLevel(logging.DEBUG)
logger.info("merhaba") # written to app.logYou can give the file path relative to the app directory; logs accumulate in the file as the app runs.
Adding handlers
A handler is added to a logger with logger.addHandler(handler). A logger can have many handlers; for example, two handlers can write both to a file and the screen.
logger.addHandler(logging.FileHandler("app.log"))
logger.addHandler(logging.StreamHandler())Handlers can have separate levels; this is useful to show only errors on the screen while writing all messages to the file. To remove a handler, call removeHandler.
Practice Write to a file with FileHandler and read it
Start with import logging. Define handler = logging.FileHandler("app.log"). Add handler.setFormatter(logging.Formatter("%(levelname)s:%(message)s")). Get logger = logging.getLogger("myapp"). Do logger.addHandler(handler) and logger.setLevel(logging.DEBUG). Write logger.info("merhaba"). Then read the file with open("app.log", "r", encoding="utf-8") and print its content with print(f.read().strip()).
Starter code
# import the logging module
# define a FileHandler to 'app.log'
# set a format on the handler (level:message)
# get the 'myapp' logger, add the handler and set level DEBUG
# write 'merhaba' at info level
# read the file and print its contentSample solution
import logging
handler = logging.FileHandler("app.log")
handler.setFormatter(logging.Formatter("%(levelname)s:%(message)s"))
logger = logging.getLogger("myapp")
logger.addHandler(handler)
logger.setLevel(logging.DEBUG)
logger.info("merhaba")
with open("app.log", "r", encoding="utf-8") as f:
print(f.read().strip())Expected output
INFO:merhaba
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which parameter does FileHandler take for the file path?
- output
- path
- file
- filename Correct answer
Explanation: FileHandler takes the file path as its first parameter (filename).
2 Complete the FileHandler call
import logging
handler = logging.____("app.log")import logging
handler = logging.FileHandler("app.log")Explanation: logging.FileHandler('app.log') creates a file handler.
3 Match the FileHandler concepts
| Term | Meaning |
|---|---|
FileHandler |
Writes to a file |
addHandler |
Adds a handler |
setFormatter |
Sets the format |
StreamHandler |
Writes to the screen |