When scenarios ran successful

When a scenario runs successfuly it outputs ... OK at the end of each successful step, for example:

$ python calculator.py
Story: Specifying my new calculator
As a lazy mathematician
I want to use a calculator
So that I don't waste my time thinking

Scenario 1: Sum of 1 and 1
Given I have a calculator ... OK When I enter with 1 + 1 ... OK Then I have 2 as result ... OK
Ran 1 scenarios with 0 failures, 0 errors and 0 steps pending

When scenarios fail

When a scenario fail somewhere, due to any kind of exception, it put ... FAIL in the end of step line and outputs the Exception message in the Fails part (in the end of the scenario), for example:

$ python calculator.py
Story: Specifying my new calculator
As a lazy mathematician
I want to use a calculator
So that I don't waste my time thinking

Scenario 1: Sum of 1 and 1
Given I have a calculator ... OK When I enter with 1 + 1 ... OK
Then I have 2 as result ... FAIL
Ran 1 scenarios with 0 failures, 0 errors and 0 steps pending

So, the basic idea is to output OK when it is successful and FAIL when it was not successful

It's not possible to know where exactly the error occurred (line, statement or expression), but if you write well your stories, you will know where look for and it will be easy to fix.