extracting values based on key in a dictionary

Question

I have text file having two columns: 1) column 1 is in the format yyyy-mm-dd and 2) column 2 is precipitation.

Objective: to extract original value of precipitation from column 2 only for month April, May, june, July, and August (4,5,6,7,8).

Procedure: Used line.split to extract only mm from yyyy-mm-dd format from column-1.

• made dictionary to get month and precipitation value.
• using for k,v in dct.items() and then using a if statement to extract the corresponding month precipitation value from dictionary

Problem: I can successfully print k,v (month and precipitation) from dictionary items. However, when I am using a if statement to extract the specific month's precipitation value, I am getting blank array. I was wondering can I use .append to get precipitation in (1.8,2.1,3.3) format.

Code:

file1 = open("test.txt","r")

Growing=[]
Intermediate=[]
Dormant=[]

for line in file1:
    line2 = line.split()
    WQ = line2[1]
    month = line2[0].split("-")[1]
    dct1={month:WQ}
    for k,v in dct1.items():
        if (k ==4 or k==5 or k==6 or k==7 or k==8):
            Growing.append(dct1 [k])
    print Growing

Answer 1

A more obvious structure would be a dictionary of lists:

data = collections.defaultdict()

and in the loop

data.setdefault( month,[]).append( WQ )

and then later you can access each month's data by key.

Perhaps an easier way would be to use numpy.loadtxt,

map = {'jan':1,'feb':2,'mar':3,'apr':4,'may':5} # and the rest
data = numpy.loadtxt("test.txt",dtype = dtype([('month','S4'),('WQ',float)]))

and then select

data[data['month']=='apr']['WQ']