--- Blake Winton firstname.lastname@example.org wrote:
Steve Howell wrote:
Let the Python interpreter build expression
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
row['deptno'] == 10
My language here was imprecise. I should have said something to the effect of this:
The interpreter would translate the "rowexpr" into bytecode that would execute the same way as the "lambda" example given the scope of the method convert_to_euros in the example above.
Also, the bytecode would not be the "same" as the lambda; it would just have similar complexity.
I'm sorry, why would that not be translated into:
lambda row: row['convert_to_euros'](row['salary'] > row['50000'] row['and'] row['deptno'] == row['10']
I am suggesting that in a rowexpr expression, instead of the typical local scope being the default scope, "row" would be the local scope for dereferencing. Since I am proposing an expression syntax, does not the local scope go away?
If you look at where salary, row, and deptno sit in the expression, it seems pretty clear to me that a well-defined scoping scheme would try to dereference row by default for all those tokens, and probably give up there, throwing an exception.
The convert_to_euros token in the expression obviously poses a thornier problem. Do you prefer row.convert_to_euros, if such a think exists, or do you go right to what would be the typical scope of a similar lambda expression, and prefer, say, the definition of "def convert_to_euros" that sits at the module level? I would think the latter.
The interpreter surely can evaluate such an expression and determine that convert_to_euros is going to be used a callable. Now, whether convert_to_euros is actually callable at run time is another story, but if it isn't, an exception is thrown, and at least you're not debugging somebody else's library to figure out why. Python would just tell you.
I don't mean to oversimplify this, which is why I'm batting it around on a forum with a lot of smart people. But clearly it could be done. Whether it *should* be done is, of course, a question for debate, and I accept this.
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