gistfile1.py

rom flask import Flask

app = Flask(__name__)

@app.teardown_request
def teardown(exc = None):
    if exc is not None:
        print "An exception has occured!"

try:
    with app.test_request_context():
        raise Exception('dummy')
except:
    pass

# uncomment this to remove the issue
# import sys; sys.exc_clear()

with app.test_request_context():
    print "Nothing happening here"
    
# Output:
# An exception has occured!
# Nothing happening here
# An exception has occured! <== this is unexpected!