python - Why does Pycharm's inspector complain about "d = {}"?

206
votes

When initializing a dictionary with d = {} Pycharm's code inspector generates a warning, saying

This dictionary creation could be rewritten as a dictionary literal.

If I rewrite it d = dict() the warning goes away. Since {} already is a dictionary literal, I'm pretty sure the message is erroneous. Furthermore, it seems like both d = {} and d = dict() are valid and Pythonic.

This related question seems to conclude that the choice is just a matter of style/preference: differences between "d = dict()" and "d = {}"

Why would Pycharm complain about d = {}?

UPDATE:

Mac nailed it. The warning actually applied to multiple lines, not just the one that was flagged.

Pycharm seems to look for a sequence of consecutive statements where you initialize a dictionary and then set values in the dictionary. For example, this will trigger the warning:

d = {}
d['a'] = 1

But this code will not:

d = {}
pass
d['a'] = 1
5
pythonpycharm
too noisy, and there is no real performance gain, just one more superfluous inspection – dashesy
Same thing happens for lists: a = [1]; a.append(2), probably because a=[1, 2] is nicer .... – cleros
yup. annoying message. all those underlines by PyCharm makes one uncomfortable before executing the program. – Rajkumar R
I found similar issue in JetBrains YouTrack - youtrack.jetbrains.com/issue/PY-19269#u=1461253420326 and it says: In this case PyCharm suggests that you can provide the value for the something attribute right into the dict literal instead of assigning it at the next line. – Dudnikof

5 Answers

257
votes

What is the following code to your dictionary declaration?

I think pycharm will trigger the error if you have something like:

dic = {}
dic['aaa'] = 5

as you could have written

dic = {'aaa': 5}

BTW: The fact that the error goes away if you use the function doesn't necessarily mean that pycharm believes dict() is a literal. It could just mean that it doesn't complain for:

dic = dict()
dic['aaa'] = 5

HTH!

19
votes

This can be disabled in the Project Settings or Default Settings.

  • Navigate to Settings -> Inspections -> Python
  • Uncheck "Dictionary creation could be rewritten by dictionary literal"
11
votes

for those who like (just like me) to initialize dictionaries with single operation 

d = {
  'a': 12,
  'b': 'foo',
  'c': 'bar'
}

instead of many lines like

d = dict()
d['a'] = 12
d['b'] = ....

in the end I ended up with this:

d = dict()
d.update({
  'a': 12,
  'b': 'foo',
  'c': 'bar'
})

Pycharm is not complaining on this

0
votes
mydict = {
  a: 5,
  b:z+c/2
}

The dictionary could have been created directly without initialising them first and then reassigning new values.

0
votes

I have a situation where this warning is bugging the hell out of me. In my case, I'm populating my dict partially as literals and partially from a tuple output by a function, like so:

def get_other_values():
    return 3, 4

foo = {
    "a": 1,
    "b": 2
}
foo["c"], foo["d"] = get_other_values()

So, unless I create interim vars for the output of get_other_values, PEP8 generates this warning even though I'm creating the dict with literals. And I can't assign the c and d keys in the literal, since the values are output as a tuple.