[Buy Me a Coffee](ko-fi.com/superkai)☕ *[My post](https://dev.to/hyperkai/warning-in-python-415g) explains **Warning** with [warn()](https://docs.python.org/3/library/warnings.html#warnings.warn) in Python. [A warnings filter](https://docs.python.org/3/library/warnings.html#the-warnings-filter) can set which warnings to show using these filters(`actions`) below. *`"once"` may not work properly: |Value|Disposition| |-|-| |`"default"`|print the first occurrence of matching warnings for each location (module + line number) where the warning is issued| |"error"|turn matching warnings into exceptions| |"ignore"|never print matching warnings| |"always"|always print matching warnings| |"module"|print the first occurrence of matching warnings for each module where the warning is issued (regardless of line number)| |"once"|print only the first occurrence of matching warnings, regardless of location| By default, these filters below are set to `warnings.filters` and they can be reset with [resetwarnings()](https://docs.python.org/3/library/warnings.html#warnings.resetwarnings) as shown below: ```python import warnings print(warnings.filters) # [('default', None, , '__main__', 0), # ('ignore', None, , None, 0), # ('ignore', None, , None, 0), # ('ignore', None, , None, 0), # ('ignore', None, , None, 0)] warnings.resetwarnings() print(warnings.filters) # [] ``` Now, [filterwarnings()](https://docs.python.org/3/library/warnings.html#warnings.filterwarnings) or [simplefilter()](https://docs.python.org/3/library/warnings.html#warnings.simplefilter) can filter warnings as shown below: *Memos for `filterwarnings()`: - The 1st argument is `action`(Required-Type:`str`). *`"default"`, `"error"`, `"ignore"`, `"always"`, `"module"` or `"once"` can be set. - The 2nd argument is `message`(Optional-Default:`""`-Type:`str`). - The 3rd argument is `category`(Optional-Default:[Warning](https://docs.python.org/3/library/exceptions.html#Warning)-Type:`Warning`). - The 4th argument is `module`(Optional-Default:`""`-Type:`str`). *It may not work properly. - The 5th argument is `lineno`(Optional-Default:`0`-Type:`int`): *Memos: - It decides a line number. - It must be `x >= 0`. - The 6th argument is `append`(Optional-Default:`False`-Type:`bool`). *If it's `False`, a filter is add before other filters while if it's `True`, a filter is add after other filters. *Memos for `simplefilter()`: - The 1st argument is `action`(Required-Type:`str`). *`"default"`, `"error"`, `"ignore"`, `"always"`, `"module"` or `"once"` can be set. - The 2nd argument is `category`(Optional-Default:[Warning](https://docs.python.org/3/library/exceptions.html#Warning)-Type:`Warning`). - The 3rd argument is `lineno`(Optional-Default:`0`-Type:`int`): *Memos: - It decides a line number. - It must be `x >= 0`. - The 4th argument is `append`(Optional-Default:`False`-Type:`bool`). *If it's `False`, a filter is add before other filters while if it's `True`, a filter is add after other filters. ``` my_project |-main.py |-file1.py(module) └-file2.py(module) ``` `file1.py`: ```python import warnings # Line 1 # Line 2 warnings.warn(message="Warning 1", category=UserWarning) # Line 3 warnings.warn(message="Warning 2", category=DeprecationWarning) # Line 4 warnings.warn(message="Warning 2", category=DeprecationWarning) # Line 5 warnings.warn(message="Warning 3", category=UserWarning) # Line 6 ``` `file2.py`: ```python import warnings # Line 1 # Line 2 warnings.warn(message="Warning 1", category=UserWarning) # Line 3 warnings.warn(message="Warning 2", category=DeprecationWarning) # Line 4 warnings.warn(message="Warning 2", category=DeprecationWarning) # Line 5 warnings.warn(message="Warning 3", category=UserWarning) # Line 6 ``` `main.py` with `"default"` filter(`action`): ```python import warnings warnings.resetwarnings() warnings.filterwarnings(action="default") warnings.filterwarnings(action="default", message="", category=Warning, module="", lineno=0, append=False) warnings.simplefilter(action="default") warnings.simplefilter(action="default", category=Warning, lineno=0, append=False) print(warnings.filters) # [('default', None, , None, 0)] import file1, file2 # ...\my_project\file1.py:3: UserWarning: Warning 1 # warnings.warn(message="Warning 1", category=UserWarning) # ...\my_project\file1.py:4: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) # ...\my_project\file1.py:5: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) # ...\my_project\file1.py:6: UserWarning: Warning 3 # warnings.warn(message="Warning 3", category=UserWarning) # ...\my_project\file2.py:3: UserWarning: Warning 1 # warnings.warn(message="Warning 1", category=UserWarning) # ...\my_project\file2.py:4: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) # ...\my_project\file2.py:5: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) # ...\my_project\file2.py:6: UserWarning: Warning 3 # warnings.warn(message="Warning 3", category=UserWarning) ``` `main.py` with `"error"` filter(`action`): ```python import warnings warnings.resetwarnings() warnings.filterwarnings(action="error") warnings.simplefilter(action="error") print(warnings.filters) # [('error', None, , None, 0)] import file1, file2 # ...\my_project\file1.py", line 3, in # warnings.warn(message="Warning 1", category=UserWarning) # UserWarning: Warning 1 ``` `main.py` with `"ignore"` filter(`action`): ```python import warnings warnings.resetwarnings() warnings.filterwarnings(action="ignore") warnings.simplefilter(action="ignore") print(warnings.filters) # [('ignore', None, , None, 0)] import file1, file2 # Warnings are not shown ``` ```python import warnings warnings.resetwarnings() warnings.filterwarnings(action="ignore", category=UserWarning) warnings.simplefilter(action="ignore", category=UserWarning) print(warnings.filters) # [('ignore', None, , None, 0)] import file1, file2 # ...\my_project\file1.py:4: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) # ...\my_project\file1.py:5: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) # ...\my_project\file2.py:4: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) # ...\my_project\file2.py:5: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) ``` ```python import warnings warnings.resetwarnings() warnings.filterwarnings(action="ignore", message="Warning 1", category=UserWarning) print(warnings.filters) # [('ignore', re.compile('Warning 1', re.IGNORECASE), # , None, 0)] import file1, file2 # ...\my_project\file1.py:4: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) # ...\my_project\file1.py:5: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) # ...\my_project\file1.py:6: UserWarning: Warning 3 # warnings.warn(message="Warning 3", category=UserWarning) # ...\my_project\file2.py:4: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) # ...\my_project\file2.py:5: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) # ...\my_project\file2.py:6: UserWarning: Warning 3 # warnings.warn(message="Warning 3", category=UserWarning) ``` ```python import warnings warnings.resetwarnings() warnings.filterwarnings(action="ignore", lineno=6) warnings.simplefilter(action="ignore", lineno=6) print(warnings.filters) # [('ignore', None, , None, 6)] import file1, file2 # ...\my_project\file1.py:3: UserWarning: Warning 1 # warnings.warn(message="Warning 1", category=UserWarning) # ...\my_project\file1.py:4: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) # ...\my_project\file1.py:5: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) # ...\my_project\file2.py:3: UserWarning: Warning 1 # warnings.warn(message="Warning 1", category=UserWarning) # ...\my_project\file2.py:4: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) # ...\my_project\file2.py:5: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) ``` `main.py` with `"always"` filter(`action`): ```python import warnings warnings.resetwarnings() warnings.filterwarnings(action="always") warnings.simplefilter(action="always") print(warnings.filters) # [('always', None, , None, 0)] import file1, file2 # ...\my_project\file1.py:3: UserWarning: Warning 1 # warnings.warn(message="Warning 1", category=UserWarning) # ...\my_project\file1.py:4: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) # ...\my_project\file1.py:5: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) # ...\my_project\file1.py:6: UserWarning: Warning 3 # warnings.warn(message="Warning 3", category=UserWarning) # ...\my_project\file2.py:3: UserWarning: Warning 1 # warnings.warn(message="Warning 1", category=UserWarning) # ...\my_project\file2.py:4: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) # ...\my_project\file2.py:5: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) # ...\my_project\file2.py:6: UserWarning: Warning 3 # warnings.warn(message="Warning 3", category=UserWarning) ``` `main.py` with `"module"` filter(`action`): ```python import warnings warnings.resetwarnings() warnings.filterwarnings(action="module") warnings.simplefilter(action="module") print(warnings.filters) # [('module', None, , None, 0)] import file1, file2 # ...\my_project\file1.py:3: UserWarning: Warning 1 # warnings.warn(message="Warning 1", category=UserWarning) # ...\my_project\file1.py:4: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) # ...\my_project\file1.py:6: UserWarning: Warning 3 # warnings.warn(message="Warning 3", category=UserWarning) # ...\my_project\file2.py:3: UserWarning: Warning 1 # warnings.warn(message="Warning 1", category=UserWarning) # ...\my_project\file2.py:4: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) # ...\my_project\file2.py:6: UserWarning: Warning 3 # warnings.warn(message="Warning 3", category=UserWarning) ``` `main.py` with `"once"` filter(`action`): ```python import warnings warnings.resetwarnings() warnings.filterwarnings(action="once") warnings.simplefilter(action="once") print(warnings.filters) # [('once', None, , None, 0)] import file1, file2 # ...\my_project\file1.py:3: UserWarning: Warning 1 # warnings.warn(message="Warning 1", category=UserWarning) # ...\my_project\file1.py:4: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) # ...\my_project\file1.py:6: UserWarning: Warning 3 # warnings.warn(message="Warning 3", category=UserWarning) # ...\my_project\file2.py:3: UserWarning: Warning 1 # warnings.warn(message="Warning 1", category=UserWarning) # ...\my_project\file2.py:4: DeprecationWarning: Warning 2 # warnings.warn(message="Warning 2", category=DeprecationWarning) # ...\my_project\file2.py:6: UserWarning: Warning 3 # warnings.warn(message="Warning 3", category=UserWarning) ``` `main.py` with `append` argument. *If `append=False`, a filter is add before other filters while if `append=True`, a filter is add after other filters: ```python import warnings warnings.resetwarnings() print(warnings.filters) # [] warnings.filterwarnings(action="default", append=False) warnings.simplefilter(action="default", append=False) print(warnings.filters) # [('default', None, , None, 0)] warnings.filterwarnings(action="always", append=False) warnings.simplefilter(action="always", append=False) print(warnings.filters) # [('always', None, , None, 0), # ('default', None, , None, 0)] warnings.filterwarnings(action="once", append=True) warnings.simplefilter(action="once", append=True) print(warnings.filters) # [('always', None, , None, 0), # ('default', None, , None, 0), # ('once', None, , None, 0)] ```

warningfilter

Warning Filter in Python

Join Our Newsletter. No Spam, Only the good stuff.