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Explicit returns mixed with implicit (fall through) returns

ID: py/mixed-returns
Kind: problem
Security severity: 
Severity: recommendation
Precision: high
Tags:
   - reliability
   - maintainability
Query suites:
   - python-security-and-quality.qls

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When a function contains both explicit returns (return value) and implicit returns (where code falls off the end of a function) this often indicates that a return statement has been forgotten. It is best to return an explicit return value even when returning None because this makes it easier for other developers to read your code.

Recommendation

Add an explicit return at the end of the function.

Example

In the check_state1 function, the developer probably did intend to use an implicit return value of None as this equates to False. However, the function in check_state2 is easier to read.

    def check_state1(state, interactive=True):
        if not state['good'] or not state['bad']:
            if (good or bad or skip or reset) and interactive:
                return                                          # implicitly return None
            if not state['good']:
                raise util.Abort(_('cannot bisect (no known good revisions)'))
            else:
                raise util.Abort(_('cannot bisect (no known bad revisions)')) 
        return True  							                              
           
    def check_state2(state, interactive=True):
        if not state['good'] or not state['bad']:
            if (good or bad or skip or reset) and interactive:
                return False                                    # return an explicit value
            if not state['good']:
                raise util.Abort(_('cannot bisect (no known good revisions)'))
            else:
                raise util.Abort(_('cannot bisect (no known bad revisions)'))
        return True

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