Find the max number of elements in lists as value in a dictionary

[Jon Ribbens]

On 2016-05-25, Daiyue Weng <daiyueweng at gmail.com> wrote:
> I want to find the maximal number of elements contained in a nested
> dictionary, e.g.
>
> data = {
>         'violations':
>          {
>             'col1': {'err': [elem1, elem2, elem3]},
>             'col2': {'err': [elem1, elem2]}
>          }
>         }
>
> so to find the maximal number of elements in the lists for key 'err' in key
> 'col1' and 'col2'. Also key 'violations' may contain many keys (e.g. 'col1'
> , 'col2', 'col3' etc), so what's the best way to do this (using a loop)?
>
> max = 0for col in data.violations:
>    if max < len(data.violations.col.err):
>       max = len(data.violations.col.err)

In Python 3 you could do:

  max((len(col["err"]) for col in data["violations"].values()), default=0)

In Python 2 you can do the same but you can't specify "default=0" and
so it will throw an exception if there are no lists found, so you
could use something like:

  max_errs = 0
  if data["violations"]:
      max_errs = max(len(col["err"]) for col in data["violations"].values())