Professional IronPython

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CHAPTER 12
Debugging ironPython APPlicAtions
FIgURE 12-5: 
Use formatwarning() to see how your warning will appear.
Of course, it’s handy to know the arguments for the 
formatwarning()
function. The following list 
provides a brief description of each argument.
➤➤
Message: The message you want to display to the user.
➤
➤
Category: The warning category you want to use.
➤
➤
Filename: The name of the file where the warning occurred (not necessarily the current file).
➤
➤
Line number: In most cases, this value contains the line at which the warning is detected, which 
isn’t always the line at which the warning occurs. For example, it’s possible for a warning to 
appear at the end of a structure, rather than at the appropriate line within the structure.
➤
➤
Line of code: An optional entry that shows the line of code at which the warning occurs. 
If you don’t supply this argument, the 
formatwarnings()
function defaults to a value of 
None
. The IronPython implementation differs from the standard in this regard. According 
to the standard, the interpreter is supposed to read the file, obtain the correct line of code, 
and display the specified line when you don’t provide the appropriate text.
Working with Categories
A warning category is a means of identifying a particular kind of warning. The category makes it pos-
sible to group like warnings together and reduces the risk that someone will misinterpret the meaning 
of a message. In short, a category is a way to pigeonhole a particular message so that others know 
what you intend. Of course, filtering considers the warning category, so you also need to use the cor-
rect category to ensure filtering works as expected. Table 12-3 contains a list of the warning message 
categories, including a general 
Warning
class that you shouldn’t ever use because it’s too general.