How to change the message in a Python AssertionError?
Solution 1:
assert expression, info
For instance,
>>> assert False, "Oopsie"
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AssertionError: Oopsie
From the docs:
Assert statements are a convenient way to insert debugging assertions into a program:
assert_stmt ::= "assert" expression ["," expression]
The simple form,
assert expression
, is equivalent toif __debug__: if not expression: raise AssertionError
The extended form
assert expression1, expression2
is equivalent to
if __debug__: if not expression1: raise AssertionError(expression2)
These equivalences assume that
__debug__
andAssertionError
refer to the built-in variables with those names. In the current implementation, the built-in variable__debug__
is True under normal circumstances, False when optimization is requested (command line option -O). The current code generator emits no code for an assert statement when optimization is requested at compile time. Note that it is unnecessary to include the source code for the expression that failed in the error message; it will be displayed as part of the stack trace.
Solution 2:
Use e.args
, e.message
is deprecated.
try:
assert False, "Hello!"
except AssertionError as e:
e.args += ('some other', 'important', 'information', 42)
raise
This preserves the original traceback. Its last part then looks like this:
AssertionError: ('Hello!', 'some other', 'important', 'information', 42)
Works in both Python 2.7 and Python 3.
Solution 3:
You want to take the caught exception, convert it to a string, combine it with some additional string info, and raise a new exception.
x = 3
y = 5
try:
assert( x == y )
except AssertionError, e:
raise( AssertionError( "Additional info. %s"%e ) )
Solution 4:
You can pass the desired message when creating the exception.
raise AssertionError(line1 + ' != ' + line2)
Hope this helps.