nested dictionary assignment goes too far

[Jake Emerson]

I'm attempting to build a process that helps me to evaluate the
performance of weather stations. The script below operates on an MS
Access database, brings back some data, and then loops through to pull
out statistics. One such stat is the frequency of reports from the
stations ('char_freq'). I have a collection of methods that operate on
the data to return the 'char_freq' and this works great. However, when
the process goes to insert the unique 'char_freq' into a nested
dictionary the value gets put into ALL of the sub-keys for all of the
weather stations. I have isolated (I think) the problem to the compound
key assignment in the next-to-last line before the print statements.
The result is that the last 'freq' to run throught the for loops gets
posted to all of the sensor_numbers.  Eventually the process will put
in stats for the other keys in the nested dictionary, so that's why I
have set up the dictionary this way.

Thanks in advance!

run_flag=1
if run_flag > 0:

   distinctID = runSQL(Unique_IDs)
   distinctID = map(firstpart,distinctID) # converts the list of tuples
that is returned to a list of numbers
   rain_raw_dict =
dict.fromkeys(distinctID,{'N':-6999,'char_freq':-6999,'tip1':-6999,'tip2':-6999,'tip3':-6999,'tip4':-6999,'tip5':-6999,'tip6':-6999,'lost_rain':-6999})

   rawList = runSQL(Rain_Raw_Count)

   temp_list = [110,140,650,1440]

   for sensor_count, sensor_number in enumerate(temp_list):
      # get the frequency of timer reports for each rain gauge
      # note that when a for loop is of the form "for X, x in
enumerate(xList)",
      #     X is an index value, and x is the value itself.
      timerList = []
      for icount, i in enumerate(rawList):
         if i[0]==sensor_number:
            for jcount in range(icount+1,len(rawList)): # look ahead to
the next values for comparison
               if rawList[jcount][0]==sensor_number:
                  if rawList[icount][2]==rawList[jcount][2]:
                     temp = rawList[jcount][1]-rawList[icount][1]
                     timerList.append(temp)
                     icount = jcount-1
                     break

      # now build a histogram of the time differences stored in
"timerList"
      h = Histogram()
      timer = h.histo(timerList)
      sorted_timer = h.sorted_histo(timer)
      freq = h.characteristic_freq(sorted_timer)
      rain_raw_dict[sensor_number]['char_freq'] = sensor_number   #
<<<< here's the problem!!
      freq = -6999

print "ID = 110:",rain_raw_dict[110]
print "ID = 140:",rain_raw_dict[140]
print "ID = 650:",rain_raw_dict[650]
print "ID = 1440:",rain_raw_dict[1440]