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+--- Thread: Recursion, with "some_dict={}" function parameter. (/thread-20244.html)
Recursion, with "some_dict={}" function parameter. - MvGulik - Aug-02-2019
I'm not getting some python(3.5.2) behaviour.
I got a function
def get_links_titles( links_list, titles_dict={}, r=0 ):. (Key-part: titles_dict={})In it I recall(recursion) it with
titles_del = get_links_titles( case_dict['redirlinks'], {}, r=r+1 ) it works as intended. The recursive case start with an empty titles_dict case.But when I don't use the
, {} part, and use titles_del = get_links_titles( case_dict['redirlinks'], r=r+1 )The
titles_dict in the recursion case is not empty, but contains the data titles_dict had before the recursive call. (???).Ergo: What Python behaviour rule(s) I'm I missing to make sense of that last case.
---
Mmm, seems that
titles_dict={} as function parameter is not a good idea based on some similar down the line unsuspected hiccup.So ditched it in the def-part and moved it inside the function. (not needed in def + wip function. re-investigate later.)
RE: Recursion, with "some_dict={}" function parameter. - fishhook - Aug-02-2019
Dictionaries are objects that are always passed as links to the original. Never do the following:
def get_links_titles( links_list, titles_dict={}, r=0 ):
passin this case, you will have only one object titles_dict through all of the function calls. Do like this:def get_links_titles(links_list, titles_dict=None, r=0):
titles_dict = titles_dict or {}
RE: Recursion, with "some_dict={}" function parameter. - ThomasL - Aug-02-2019
The same is with lists as default arguments
https://nikos7am.com/posts/mutable-default-arguments/
RE: Recursion, with "some_dict={}" function parameter. - MvGulik - Aug-02-2019
Aha. Its starting to make more sense to me now.
Definitely a subject I need to explore some more (todo). Additional Link definitely going to help with that.
(I think I used this ones to my benefit, but without actually realising why or how it worked)
Thanks for putting me on the right track. :-)