[Python-Dev] Pre-PEP: Allow Empty Subscript List Without Parentheses (original) (raw)

Shane Hathaway shane at hathawaymix.org
Sun Jun 18 09:54:36 CEST 2006

Noam Raphael wrote:

2006/6/17, "Martin v. Löwis" <martin at v.loewis.de>:

Noam Raphael wrote:

I meant the extra code for writing a special class to handle scalars, if I decide that the "x[()]" syntax is too ugly or too hard to type, so I write a special class which will allow the syntax "x.value". What I cannot understand is why you use a zero-dimensional array to represent a scalar. Scalars are directly supported in Python:

x = 5 I need a zero-dimensional array as a single cell - an object that holds a value that can change over time. It works just like a cell in a spreadsheet: For example, say that if you change the value of cell A1 to 0.18, cell A2 changes to 5. When using the library I design, you would write "sheet1[0, 0] = 0.18", and, magically, "sheet1[0, 1]" will become 5. But in my library, everything is meaningful and doesn't have to be two-dimensional. So, if in the spreadsheet example, A1 meant the income tax rate, you would write "incometax[] = 0.18", and, magically, "profit['Jerusalem', 2005]" will become 5.

Try to think more about how users will use your API. You haven't specified where those names (sheet1, income_tax, and profit) are coming from. What do you expect users of your library to do to bring those names into their namespace?

Let me take a wild guess so you can see what I'm asking:

import spreadsheetlib sheet1 = spreadsheetlib.sheet('sheet1') income_tax = spreadsheetlib.cell('income_tax') profit = spreadsheetlib.cell('profit')

So far, that's a mess! What are you really going to do? Will it be better? This could be a much greater concern than optimizing away parentheses.

A possible way to solve the namespace problem is to make all names an attribute of some object.

from spreadsheetlib import sp sp.sheet1[0, 0] = 0.18 assert sp.sheet1[0, 1] == 5 sp.income_tax = 0.18 assert sp.profit['Jerusalem', 2005] == 5

That would be a pretty usable API, IMHO, and you'd be able to write it now without any changes to Python.

Shane

More information about the Python-Dev mailing list