Ben Finney wrote: > Steven D'Aprano <steve+comp.lang.pyt...@pearwood.info> writes: > >> LJ wrote: >> >> > def gt(l): >> > a["1"] = a["1"] | set([l]) >> >> The difference between this example and your second one: >> >> > def gt2(l): >> > b=b+l >> >> >> is that the second is a "binding operation" and the first is not. > > I disagree; they're both binding operations (and they both use the > binding operator ‘=’ to express this).
Define "operator" :-) In Python terms, operators include + - * etc. They return a result, and are implemented by a special __dunder__ method. (Sometimes by two dunder methods, e.g. __add__ and method __radd__.) By this definition, = is not an operator. And indeed, the Python docs don't list = as an operator: https://docs.python.org/2/reference/lexical_analysis.html#operators but it is listed as a delimiter: https://docs.python.org/2/reference/lexical_analysis.html#delimiters That's why I was careful to use the term "binding operation" and avoid "operator", although I admit that was pretty subtle :-) As for the rest of your comments: > The difference between the two is: what reference is being bound? I don't think we disagree, we merely have a different emphasis. The rules for assignments in Python are a bit complicated, and the official language used is often different from what we say informally: https://docs.python.org/2/reference/simple_stmts.html#assignment-statements Of course you are right that other assignment statements bind a value to a reference of some sort: spam.method().attribute['key'].thingy[0] = eggs but *not for the purpose of deciding what is a local variable*. That was the point I was emphasising. The docs referenced above say: Assignment of an object to a single target is recursively defined as follows. If the target is an identifier (name): If the name does not occur in a global statement in the current code block: the name is bound to the object in the current local namespace. Otherwise: the name is bound to the object in the current global namespace. which is a little less than clear, but basically it means that assignments of the form: name = something force name to be a local variable unless it is explicitly declared global. More information here: https://docs.python.org/2/reference/simple_stmts.html#the-global-statement Oh, I learned something new: strictly speaking, this is implementation- dependent and not guaranteed to work in the future! def func(): global math import math -- Steven -- https://mail.python.org/mailman/listinfo/python-list
