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[1.7.x] Fixed #22412 -- More nuanced advice re template filters and e…

…xceptions.

Thanks Tim for review.

Backport of 7e3834a from master
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1 parent 941f947 commit 0b43308e2de5dcac67b530bb03376655dfb61cef @carljm carljm committed with timgraham Apr 9, 2014
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  1. +5 −3 docs/howto/custom-template-tags.txt
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8 docs/howto/custom-template-tags.txt
@@ -88,9 +88,11 @@ Custom filters are just Python functions that take one or two arguments:
For example, in the filter ``{{ var|foo:"bar" }}``, the filter ``foo`` would be
passed the variable ``var`` and the argument ``"bar"``.
-Filter functions should always return something. They shouldn't raise
-exceptions. They should fail silently. In case of error, they should return
-either the original input or an empty string -- whichever makes more sense.
+Usually any exception raised from a template filter will be exposed as a server
+error. Thus, filter functions should avoid raising exceptions if there is a
+reasonable fallback value to return. In case of input that represents a clear
+bug in a template, raising an exception may still be better than silent failure
+which hides the bug.
Here's an example filter definition:

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