from datetime import datetime
from collections import OrderedDict # For python 2.7 and above
data = { "01-01-2015" : "some data",
"05-05-2015" : "some data",
"03-04-2015" : "some data" }
# For python 2.7 and above:
ordered_data = OrderedDict(
sorted(data.items(), key = lambda x:datetime.strptime(x[0], '%d-%m-%Y')) )
# For python 2.6 and below where OrderedDict is not present:
# ordered_data = sorted(data.items(), key = lambda x:datetime.strptime(x[0], '%d-%m-%Y'))
print(ordered_data)
#Output :
[('01-01-2015', 'some data'),
('03-04-2015', 'some data'),
('05-05-2015', 'some data')]