[Python-ideas] New 3.x restriction on number of keyword arguments (original) (raw)

Terry Reedy tjreedy at udel.edu
Fri Sep 17 23:50:00 CEST 2010

On 9/17/2010 4:00 PM, Raymond Hettinger wrote:

One of the use cases for named tuples is to have them be automatically created from a SQL query or CSV header. Sometimes (but not often), those can have a huge number of columns. In Python 2.x, it worked just fine -- we had a test for a named tuple with 5000 fields. In Python 3.x, there is a SyntaxError when there are more than 255 fields.

So, when the test failed due to the code change, the test was simply removed?

The origin of the change was a hack to fit positional argument counts and keyword-only argument counts in a single oparg in the python opcode encoding.

I do not remember any discussion of adding such a language restriction, though I could have forgotten or missed it. As near as I can tell, it is undocumented. While there are undocumented limits to the interpreter, like nesting depth, this one is so low that I would consider the discrepancy between doc and behavior a bug.

-- Terry Jan Reedy

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