[Tutor] detecting a change in a iterable object (list, array, etc.)

[Tim Michelsen]

Hello,
> A list comprehension will work for this. If data is a list of triples of 
> (year, month, volume) then this will give you a list of the 1997 triples:
> 
> data1997 = [ item for item in data if item[0]==1997 ]

I tried your code out (see below).

Here is the output:


[]
[]
[]
[]
[]
[1990, 0, 1, -18.0]
[1990, 0, 2, -0.5]
[1990, 0, 3, -14.0]
[1990, 0, 4, -21.0]

How do I avoid the []?

What whould be the easiest way to save this list (without the "[]") into a file
and append a newline after each row?

Thanks for your help in advance,
Timmie

Here's the code:
#!/usr/bin/env python
# currently used modules
import csv

# SOME VARIABLES
#~ stattion_name = 'Sosan'
input_file_name = '../data/filter_test_data.csv'
output_file_name = '../data/filter_test_data_result.csv'

# prepare files
input_file = open(input_file_name, 'r')
output_file = open(output_file_name ,'w')
header = u"Year, Month, Day, Hour_of_day [h], values, \n"
input_data = csv.reader(input_file, delimiter=';')

#~ skip the first rows
line1 = input_file.readline()
line2 = input_file.readline()

#~ write the header
output_file.write(header.encode('utf-8'))

counter = 0
value_col = 6
for line in input_data:
    #~ print line
    #~ year month day temp_3hr
    year = int(line[1])
    month = int(line[2])-1
    day = int(line[3])
    value = float(line[6])*0.5
    compact_list = [year, month, day, value]
    res_rows = [ item for item in compact_list if compact_list[0] == 1990 ]
    print res_rows
input_file.close()
output_file.close()