Custom sort Python list with certain strings always at beginning? -

i working in python 2.7. have list of strings this:

mylist = ['is_local', 'quantity_123', 'actual_cost_456',           'actual_cost_123', 'quantity_456', 'total_items_123',           'id', 'total_items_456', 'name', 'postcode'] 

the list have id, name, postcode , is_local fields in it, other fields vary.

i sort list starts set fields above, , has other fields in alphabetical order.

for example:

mylist.sort(custom_sort) print mylist ['id', 'name', 'postcode', 'is_local', 'actual_cost_123',   'actual_cost_456', 'quantity_123', 'quantity_456' ...] 

my problem how define custom_sort function. i've tried this:

def custom_sort(a, b):   if == 'id':     return 1   elif == 'name':     return 1   elif == 'postcode':     return 1   elif == 'is_dispensing':     return 1   elif > b:     return 1   else:     return -1 

but mylist.sort(custom_sort) gives me error: typeerror: argument of type 'nonetype' not iterable.

if have not duplicate elements within mylist can use set.difference method difference between custom list mylist sort , append custom list :

>>> l=['id', 'name', 'postcode', 'is_local'] >>> l+sorted(set(mylist).difference(l)) ['id', 'name', 'postcode', 'is_local', 'actual_cost_123', 'actual_cost_456', 'quantity_123', 'quantity_456', 'total_items_123', 'total_items_456'] >>>  

else can use list comprehension :

>>> l+sorted([i in mylist if not in l]) ['id', 'name', 'postcode', 'is_local', 'actual_cost_123', 'actual_cost_456', 'quantity_123', 'quantity_456', 'total_items_123', 'total_items_456'] >>>