Python Forum

the following code:

foo = {}.update(os.environ)

has a behavior that i have been unable to find documentation that describes (assuming import os has been done). does anyone know if such documentation exists and where that documentation can be found? i have PDF documentation for python version 3.5.2 but a reference in an HTML document of 3.4 or later should be good enough.

According to the documentation, the behavior is the same as foo = None.

(Feb-17-2018, 01:32 PM)Gribouillis Wrote: [ -> ]According to the documentation, the behavior is the same as foo = None.

my documentation (PDF letter format for 3.5.2) didn't give that information. maybe i need to switch back to the HTML documentation (been using PDF for 3+ years).

If you read carefully, typing pydoc3 dict.update in a terminal gives the same information.

yes, it sure does. i was not aware of this way to get python documentation.

If have a "cool" editor mouse over update

foo = {}.update(os.environ)

foo is None because the method update returns None.
You can do this technique with data types, which returns a new copy of them selfs if mutated (str does this).

It's the same pitfall like this:

sorted_list = [1,4,5,6,7,3,2].sort()

list.sort() makes an inline sort (mutating the object itself) and returns None.

i guess i am just used to methods that returned something useful. i did know about .sort but didn't think of it as another case. i usually use sorted(iterable).