Move dict_to_params to flask-specific helpers.py.

The rest of etiquette has nothing to do with URLs so this
doesn't belong in the backend helper file.

etiquette/helpers.py

@@ -122,22 +122,6 @@ def comma_space_split(s):
     s = [x for x in s if x]
     return s
 
-def dict_to_params(d):
-    '''
-    Given a dictionary of URL parameters, return a URL parameter string.
-
-    {'a':1, 'b':2} -> '?a=1&b=2'
-    '''
-    if not d:
-        return ''
-
-    params = [f'{key}={value}' for (key, value) in d.items() if value]
-    params = '&'.join(params)
-    if params:
-        params = '?' + params
-
-    return params
-
 def fit_into_bounds(image_width, image_height, frame_width, frame_height):
     '''
     Given the w+h of the image and the w+h of the frame,

frontends/etiquette_flask/etiquette_flask/endpoints/photo_endpoints.py

@@ -9,6 +9,7 @@ from voussoirkit import cacheclass
 
 from .. import common
 from .. import decorators
+from .. import helpers
 from .. import jsonify
 
 site = common.site
@@ -396,7 +397,7 @@ def get_search_core():
     if len(photos) == limit:
         next_params = original_params.copy()
         next_params['offset'] = offset + limit
-        next_params = etiquette.helpers.dict_to_params(next_params)
+        next_params = helpers.dict_to_params(next_params)
         next_page_url = '/search' + next_params
     else:
         next_page_url = None
@@ -404,7 +405,7 @@ def get_search_core():
     if offset > 0:
         prev_params = original_params.copy()
         prev_params['offset'] = max(0, offset - limit)
-        prev_params = etiquette.helpers.dict_to_params(prev_params)
+        prev_params = helpers.dict_to_params(prev_params)
         prev_page_url = '/search' + prev_params
     else:
         prev_page_url = None

frontends/etiquette_flask/etiquette_flask/helpers.py

@@ -0,0 +1,15 @@
+def dict_to_params(d):
+    '''
+    Given a dictionary of URL parameters, return a URL parameter string.
+
+    {'a':1, 'b':2} -> '?a=1&b=2'
+    '''
+    if not d:
+        return ''
+
+    params = [f'{key}={value}' for (key, value) in d.items() if value]
+    params = '&'.join(params)
+    if params:
+        params = '?' + params
+
+    return params