Sort python dictionary keys based on sub-dictionary keys by defining sorting order

Question

My question is an extension to another question where the OP has a dictionary, the one below, and wants to sort main keys based on the sub-dictionary keys

myDict = {
    'SER12346': {'serial_num': 'SER12346', 'site_location': 'North America'},
    'ABC12345': {'serial_num': 'ABC12345', 'site_location': 'South America'},
    'SER12345': {'serial_num': 'SER12345', 'site_location': 'North America'},
    'SER12347': {'serial_num': 'SER12347', 'site_location': 'South America'},
    'ABC12346': {'serial_num': 'ABC12346', 'site_location': 'Europe'}
}

The proposed (quoted below) solution works perfectly.

dicts = myDict.items()
dicts.sort(key=lambda (k,d): (d['site_location'], d['serial_num'],))

However this solution does sorting in ascending order for all (sorting in descending order is straightforward). I was wondering if it is possible to define mix of sorting order, say serial_num in ascending but site_location in descending order?

Answer 1

This is one solution, possible because list sorting is stable. I changed the data slightly to demonstrate that it works.

This method is also prescribed in the Python documentation.

myDict = {
    'SER12346': {'serial_num': 'SER12346', 'site_location': 'North America'},
    'ABC12346': {'serial_num': 'ABC12345', 'site_location': 'Europe'},
    'ABC12345': {'serial_num': 'ABC12345', 'site_location': 'South America'},
    'SER12345': {'serial_num': 'SER12345', 'site_location': 'North America'},
    'SER12347': {'serial_num': 'SER12347', 'site_location': 'South America'}
}

result = sorted(myDict.items(), key=lambda x: x[1]['site_location'], reverse=True)
result = sorted(result, key=lambda x: x[1]['serial_num'])

# [('ABC12345', {'serial_num': 'ABC12345', 'site_location': 'South America'}),
#  ('ABC12346', {'serial_num': 'ABC12345', 'site_location': 'Europe'}),
#  ('SER12345', {'serial_num': 'SER12345', 'site_location': 'North America'}),
#  ('SER12346', {'serial_num': 'SER12346', 'site_location': 'North America'}),
#  ('SER12347', {'serial_num': 'SER12347', 'site_location': 'South America'})]