Feature/membership check improvements

[KommuSoft]

Problem

Some dictionary lookups or membership checks are not done efficiently. Like if key in set(some_dict.keys()): this runs in linear time, since it first makes a set of all the keys in the dictionary.

Solution

Dropping .keys() where necessary, and if we check a dictionary to then get the corresponding value, we can replace:

if key in some_dict:
  val = some_dict[key]

by:

missing = object()
temp_val = some_dict.get(key, missing)
if temp_val is not missing:
    val = temp_val

and:

if some_key in my_dict.keys()

or:

if some_key in set(my_dict.keys())

is equivalent to just:

if some_key in my_dict

Acceptance Criteria

The tests run, and a bit faster (although that does not say much). The code just uses the fact that membership checks can be done on the dict directly, saving a few indirections.

[coveralls]

coverage: 99.913%. remained the same
when pulling 803bcbf on hapytex:feature/membership-check-improvements
into 518aa88 on django-import-export:main.

[matthewhegarty]

Thanks for submitting this.