[Python-Dev] ',' precedence in documentation] (original) (raw)

Christopher Lee leec at chem.ucla.edu
Sun Sep 14 23:01:15 CEST 2008

----- Forwarded message from Guido van Rossum <guido at python.org> -----

Note that in any case, the 'in' operator binds more tightly than the comma: e.g. f(x in y, z) means f((x in y), z).

Exactly the point I was trying to make. As far as the user's
concerned, an expression list x,y can itself be part of an expression; x in y is also an expression. Such expressions can be combined to form
larger expressions, so it follows logically that you need to know
which has precedence when both occur in an expression, e.g. whether x in y,z evaluates as (x in y),z or x in (y,z)

The page that Fredrik sent you to (http://docs.python.org/ref/exprlists.html ) doesn't address that question. I still think the precedence table (http://docs.python.org/ref/summary.html ) should show that "in" has higher precedence than comma in an
expression.

Can anyone show us "where it is written" in the Python docs that "in"
has higher precedence than comma, and why there is a good reason
that this information should NOT be included in the precedence table?

-- Chris

Adding comma to the precedence table would also disambiguate
expressions like: x and y,z x,y or z not x,y

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