Rule Definition
When a file is opened by Python, resources are allocated until the file is closed. Thus it is important to ensure the file is closed as soon as the file manipulation is done by handling correctly potential exceptions. Delegating file closing to the underlying interpreter/compiler can have a negative impact on code portability and can result in unexpected behavior.

Remediation
Use the with statement to open a file, otherwise explicitly close opened files while correctly handling exceptions arising from file manipulation.

Violation Code Sample

>>> f = open("hello.txt",'w')
>>> f.write("world")
>>> f.close()

Fixed Code Sample

>>> f = open("hello.txt", 'w')
>>> try:
>>>     f.write("world")
>>> finally:
>>>     f.close()

# or even better
>>> with open("hello.txt", 'w') as f:
>>>     f.write("world")
        

This rule is compliant with OMG CISQ ASCPEM-PRF-15, ASCRM-CWE-772 recommendations.