Deleting Dictionaries Keys with a For If Statement in Python 3

Question

I feel very dumb asking this. How do I delete a keys in a dictionary with an if statement that references the values. When I do this:

newdict = {"a":1,"b":2,"c":3}

for (key,value) in newdict:
    if value == 2:
        del newdict[key]
print(newdict)

It throws this error:

line 3, in <module>
    for (key,value) in newdict:
ValueError: not enough values to unpack (expected 2, got 1)

Thank you.

Possible duplicate of [Iterating over dictionaries using 'for' loops](https://stackoverflow.com/questions/3294889/iterating-over-dictionaries-using-for-loops) — user3483203, May 17 '18 at 18:45
When I add .items() I get RuntimeError: dictionary changed size during iteration — Aaron Mazie, May 17 '18 at 18:49
Also, if I use a dictionary comprehension {del k:v for k,v in newdict.items() if v == 2}, it throws back "SyntaxError: invalid syntax" for del — Aaron Mazie, May 17 '18 at 18:53
[How to delete items from a dictionary while iterating over it?](https://stackoverflow.com/questions/5384914/how-to-delete-items-from-a-dictionary-while-iterating-over-it) - Updated link formatting — Falt4rm, May 17 '18 at 19:01
@AaronMazie you dont want to use a dictionary comprehension for side effects. In your case, `{k: v for k, v in newdict.items() if v !=2 }` — user3483203, May 17 '18 at 19:06

M.Innat · Accepted Answer · 2018-05-17T19:23:49.337

If you need to delete based on the items value, use the items() method or it'll give ValueError. But remember if you do so it'll give a RuntimeError. This happens because newdict.items() returns an iterator not a list. So, Convert newdict.items() to a list and it should work. Change a bit of above code like following -

for key,value in list(newdict.items()):
    if value == 2:
        del newdict[key]

output -

{'a': 1, 'c': 3}

Deleting Dictionaries Keys with a For If Statement in Python 3

1 Answers1