layout.get(..., extension=bids.layout.Query.ANY) fails

layout.get assumes that the extension filter is a string or list of strings. We need to handle the Query options, as well as None.

~/Projects/bids-standard/pybids/bids/layout/layout.py in get(self, return_type, target, scope, regex_search, absolute_paths, drop_invalid_filters, **filters)
    918         if 'extension' in filters:
    919             exts = listify(filters['extension'])
--> 920             filters['extension'] = [x.lstrip('.') for x in exts]
    921 
    922         if drop_invalid_filters:

~/Projects/bids-standard/pybids/bids/layout/layout.py in <listcomp>(.0)
    918         if 'extension' in filters:
    919             exts = listify(filters['extension'])
--> 920             filters['extension'] = [x.lstrip('.') for x in exts]
    921 
    922         if drop_invalid_filters:

AttributeError: 'Query' object has no attribute 'lstrip'

[tyarkoni]

This is only failing because of a check intended to ensure backwards compatibility with people still using extensions instead of extension. We’re already issuing a warning that extensions goes away in 0.11, so I vote we just wait till 0.11 and this problem will go away by itself as soon as we remove the vestigial code.

[effigies]

The use case was determining which entities were used by a dataset.

[ent for ent in list(layout.get_entities(metadata=False))
 if layout.get(**{ent: bids.layout.Query.ANY})]

This failure required:

[ent for ent in list(layout.get_entities(metadata=False))
 if ent == 'extension' or layout.get(**{ent: bids.layout.Query.ANY})]

There might be smarter ways to go about this, but it seems silly for this to be the only entity that can’t take a Query.