ABSTRACT: I propose the following syntax: rowexpr: convert_to_euros(salary) > 50000 and deptno = 10 Rowexpr returns a function object that can be called with one argument, row, and the items "salary" and "deptno" are used to derefence row. RATIONALE: A lot of time people write Python code that works with other small interpreters, such as SQL engines, math libraries, etc., that have an expression syntax of their own. To use SQL as an example, I may want my SQL engine to use this Python expression: where convert_to_euros(salary) > 50000 and deptno = 10 To interact with SQL engines, I could imagine code like the following: sql(..., lambda row: convert_to_euros(row['salary']
50000 and row['deptno'] = 10) # not concise
sql(..., sql_parse('convert_to_euros(salary) > 50000 and deptno = 10') # requires sophisticated library sql(..., [and_op, [ge_op(func_call_op(convert_to_euros, 'salary'), 50000), eq_opt(itemgetter_op('deptno'), 10)]) # UGLY!!! SOLUTION: Let the Python interpreter build expression objects for you. You write: rowexpr: convert_to_euros(salary) > 50000 and deptno = 10 Python translates that into the same bytecode as: lambda row: convert_to_euros(row['salary'] > 50000 and row['deptno'] == 10 Benefits: 1) Allows smaller code. 2) Having Python translate the rowexpr creates an opportunity for better error messages, catching more things at startup time, etc. 3) In the particular case of SQL, it enable the development methodology that you might start off by writing code that processes data in memory, but with mostly SQL-like syntax, and then switch over to a real SQL database as scalability becomes a bigger concern. COMMON OBJECTIONS: 1) More syntax, of course. 2) Folks used to SQL would still need to adjust to differences between Python expressions (==) and SQL (=). 3) In the case of SQL, people may already be happy enough with current tools, and of course, interpreters external to Python can cache expressions, etc. OPEN QUESTIONS: Would a rowexpr be limited to dictionaries, or could it also try to access object attributes? ____________________________________________________________________________________Be a better Globetrotter. Get better travel answers from someone who knows. Yahoo! Answers - Check it out. http://answers.yahoo.com/dir/?link=list&sid=396545469