Problem – To have a program that can issue warning messages (e.g., about deprecated features or usage problems).
Code #1 : Use the
The arguments to
warn() are a warning message along with a warning class, which is typically one of the following: UserWarning, DeprecationWarning, SyntaxWarning, RuntimeWarning, ResourceWarning, or FutureWarning.
The handling of warnings depends on how the interpreter is executed and other configuration. If Python with the
-W all option is run, the following output is obtained:
bash % python3 -W all example.py example.py:5: DeprecationWarning: logfile argument is deprecated warnings.warn('logfile argument is deprecated', DeprecationWarning)
Normally, warnings just produce output messages on standard error. To turn warnings into exceptions, use the
-W error option.
Code #2 :
bash % python3 -W error example.py Traceback (most recent call last): File "example.py", line 10, in
func(2, 3, logfile ='log.txt') File "example.py", line 5, in func warnings.warn('logfile argument is deprecated', DeprecationWarning) DeprecationWarning: logfile argument is deprecated bash %
Issuing a warning message is often a useful technique for maintaining software and assisting users with issues that don’t necessarily rise to the level of being a full-fledged exception.
Code #3 : Warning message generated by destroying a file without closing it.
__main__:1: ResourceWarning: unclosed file <_io.TextIOWrapper name='/etc/passwd' mode='r' encoding='UTF-8'>
- By default, not all warning messages appear. The -W option to Python can control the output of warning messages.
- -W all will output all warning messages, -W ignore ignores all warnings, and -W error turns warnings into exceptions.
- As an alternative, one can use the warnings.simplefilter() function to control output. An argument of always makes all warning messages appear, ignore ignores all warnings, and error turns warnings into exceptions.
- The warnings module provides a variety of more advanced configuration options related to the filtering and handling of warning messages.
- Python | Reraise the Last Exception and Issue Warning
- Python | Message Encode-Decode using Tkinter
- Python | Prompt for Password at Runtime and Termination with Error Message
- hmac - Keyed-Hashing for Message Authentication
- Python | Convert list to Python array
- Reading Python File-Like Objects from C | Python
- Python | Index of Non-Zero elements in Python list
- Important differences between Python 2.x and Python 3.x with examples
- Python | Merge Python key values to list
- Python | Sort Python Dictionaries by Key or Value
- Python | Set 4 (Dictionary, Keywords in Python)
- Python | Add Logging to Python Libraries
- Python | Add Logging to a Python Script
- Python | Visualizing O(n) using Python
If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to firstname.lastname@example.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.