Question

I am very new to python programming and have yet to buy a textbook on the matter (I am buying one from the store or Amazon today). In the meantime, can you help me with the following problem I have encountered?

I have an list of dictionary objects like this:

stock = [ 
  { 'date': '2012', 'amount': '1.45', 'type': 'one'},
  { 'date': '2012', 'amount': '1.4', 'type': 'two'},
  { 'date': '2011', 'amount': '1.35', 'type': 'three'},
  { 'date': '2012', 'amount': '1.35', 'type': 'four'}
]

I would like to sort the list by the amount date column and then by the amount column so that the sorted list looks like this:

stock = [ 
  { 'date': '2011', 'amount': '1.35', 'type': 'three'},
  { 'date': '2012', 'amount': '1.35', 'type': 'four'},
  { 'date': '2012', 'amount': '1.4', 'type': 'two'},
  { 'date': '2012', 'amount': '1.45', 'type': 'one'}
]

I now think I need to use sorted() but as a beginner I am having difficulties understanding to concepts I see.

I tried this:

from operator import itemgetter
all_amounts = itemgetter("amount")
stock.sort(key = all_amounts)

but this resulted in an list that was sorted alphanumerically rather than numerically.

Can someone please tell me how to achieve this seemingly simple sort? Thank-you!

Answer 1

Your sorting condition is too complicated for an operator.itemgetter. You will have to use a lambda function:

stock.sort(key=lambda x: (int(x['date']), float(x['amount'])))

or

all_amounts = lambda x: (int(x['date']), float(x['amount']))
stock.sort(key=all_amounts)