Loop to append multiple lists to a single list in Python

Question

In the following code, row[8], row[9], ..., row[27] each contain many numbers. I need all of the numbers in row[8], row[9], etc. to append to stat_by_symbol as separate lists within within stat_by_symbol. However, the code below appends all of the numbers across all rows within a single list.

As an example of what I need, if I called stat_by_symbol['aaa'][0], then I should get the list of numbers pulled from row[8].

How can I fix this? Many thanks.

EDIT for further clarification. I've attached a snapshot of the csv. I need stat_by_symbol['aaa'][0] to give me all of the numbers under Column i. Similarly, stat_by_symbol with index 1 would give me all of the numbers under Column j.

enter image description here

stat_by_symbol = {}
with open('zzdata.csv', 'rb') as f:
 reader = csv.reader(f)
 reader.next()
 for row in reader:
 for symbol in symbols:#symbols in a list
 if symbol in row:
 for i in range(8, 28):
 stat_by_symbol.setdefault(symbol, []).append(row[i])

• Vaughn Cato: are you sure row is a list of lists?
• eumiro: @johnjdc - why do you keep unindenting the block after with?
• user1028861: @Vaughn Cato each row is a list and stat_by_symbol is supposed to collect all of those lists.
• user1028861: @eumiro I spaced over four times and then pasted the code. Not sure why. I fixed it, though.
• Vaughn Cato: @johnjdc - you said that row[8] contains many numbers, which would imply that row[8] is a list, which would imply that row is a list of lists. I think you are thinking of the variable "row" in two different ways.

Answer 1

stat_by_symbol = dict((symbol, [[] for i in xrange(8,28)]) for symbol in symbols)
with open('zzdata.csv', 'rb') as f:
 reader = csv.reader(f)
 reader.next()
 for row in reader:
 for symbol, symbol_list in stat_by_symbol.iteritems():
 if symbol in row:
 for symbol_list2, cell in zip(symbol_list, row[8:28]):
 symbol_list2.append(cell)

• user1028861: I get an error when I try to run the top line: "stat_by_symbol = dict((symbol, [[] for i in xrange(8,28)]) for symbol in symbols)" I fixed the bracket, but Python also highlights for in the top line.