dictionary - Python script to use coordinates from one file and add values from matching coordinates in another file -

i have original set of genomic coordinates (chrom, start, end) in tab delimited bed file. have additional tab delimited bed files contain of original genomic coordinates plus numerical value associated each of these coordinates. these coordinates can show multiple times in bed file different numerical value each time. need final bed file contains each of original genomic coordinates summed number of values found associated specific coordinate. examples of files i'm working below.

original file:

chr1    2100    2300  chr2    3300    3600  chr1    2560    2800 

other bed file:

chr1    2100    2300    6  chr2    3300    3600    56  chr1    2100    2300    10 

needed output file:

chr1    2100    2300    16  chr2    3300    3600    56  chr1    2560    2800    0 

i need write python script this, i'm not sure best way is.

def fetch_data(filename1, filename2):     lines = []     data = {}     open (filename1) f:         lines = f.readlines()      line in lines:         if not line.strip():             continue         data[' '.join(line.split())] = 0      open (filename2) f:         lines = f.readlines()      line in lines:         if not line.strip():             continue         arr = line.split()         data[' '.join(arr[:-1])] += int(arr[3])      return data   open ('output.txt', 'w') f:     key,value in fetch_data('original.txt','data.txt').iteritems():         f.write('{0}    {1} \n\n'.format('    '.join(key.split()), str(value)))