Professional IronPython

TAblE 12-1: 
Warning-Related Functions and Their Purpose
FUNCTIoN 
PURPoSE
filterwarnings() 
Adds rules to a warning that affects when it triggers and how the inter-
preter reacts to the warning.
formatwarning() 
Displays a warning in the standard way.
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Understanding IronPython Warnings
 
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243
FUNCTIoN 
PURPoSE
resetwarnings() 
Resets the warning state to its default settings.
showwarning() 
Displays the specified warning. You can use this function to write
the warning to a file. The function defaults to writing the warning
to the 
sys.stderr
device.
simplefilter() 
Provides a simplified version of the 
filterwarnings()
function that 
doesn’t require the use of Regular Expressions.
warn() 
Used to issue a warning of a particular category.
warn_explicit() 
Provides low-level access to the 
warn()
function so that you can out-
put extended warning information.
warnpy3k() 
Issues warnings for Python 3.x–related deprecations. This function 
doesn’t do anything unless you start IronPython using the 
–3
command 
line switch.
This chapter doesn’t describe every argument you can use with every function; 
it concentrates on actual usage instead. The site at 
http://docs.python.org/
library/warnings.html
 provides information about all of the arguments you 
can use with each of these functions.
Working with Actions
Before you do too much with warnings, it’s important to know that warnings have an action associated 
with them. For example, you can choose to turn a particular warning into an exception or to ignore it 
completely. You can apply actions to warnings in a number of ways using either the 
filterwarnings()
or 
simplefilter()
function. Table 12-2 shows the list of standard warning actions.