sympy/sympy — pull request #1324 by smichr (2012-05-31 07:00:01+00:00)
Title: Solve - return None rather than []; allow 'dict' flag for canonical return structure

With dict=True a list (perhaps empty) or a list of solution mappings will be returned from solve regardless of input:

solve(x - 3, dict=True) -> [{x: 3}]