assertionerror returning empty string in python

I am doing this:

try: self.failUnless(sel.is_text_present("F!")) #sel.is_text_present("F!") is false
except AssertionError, e: 
    print("x"+e+"y")
    sys.exit()

开发者_运维百科it is printing nothing except xy. no class name or anything else. what does the error in AssertionError normally contain?

edit: apparently the user provides its own message. selenium generated many of these:

except AssertionError, e: self.verificationErrors.append(str(e))

without sending in a message at all, so it appends a bunch of empty strings to verificationErrors.

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Don't catch the errors from assertions. All the assertions in the unittest module take a final parameter, msg, which is the message to be raised if the assertion fails. Put your debugging there if necessary.

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Standard assert statement doesn't put anything into the AssertionError, it's the traceback that matters. There is a assert expr, msg variant that sets the error message, if you're using unittest, then the second argument of assertTrue (failUnless is deprecated) will do it.

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Sounds like you want to use your assertions as debug statements in the event of a failure. This should help...

import traceback

try:
  assert 1 == 2
except AssertionError: 
  traceback.print_exc()

This prints:

Traceback (most recent call last):
  File "./foo.py", line 4, in <module>
    assert 1 == 2