Extracting data and signals from a file

Before I start, I'm just a beginner here as well as Python and I'm working on something like extracting data from a file and then from data that I need to create a data signal. I don't know how to explain it, but I will try my best to explain the problem and here's what. I was given a text file like:

12 0011
15 001a
20 111e
32 8877
50 00f3 
56 1000

      

        
        
        
      

    

I was able to read the files and put them into a dictionary:

def dictionary(filename):
 d = {}
 f = open(filename,'r')
 for lines in f:
  line = lines.split(' ',1)
  line[1] = line[1].replace('\n','')
  d[line[0]] = line[1]
 f.close()
 for k in sorted(d.keys()):
  print 'Keys:', k, '-> Values:', d[k]
 return d

      

        
        
        
      

    

Well for the second part it refers to a text file where the first column represents time and the second column represents data. This means that at time = 15 seconds, data 001a is incremented until time = 20 seconds, when data changes to 111e. The data remains unchanged (111e) until time = 32 s, where the data changes again to 8877. The same process continues. I had to extract the output produced from time = 15s to time = 60s in an interval of 1s per time. The problem is, I don't know the exact method for this part. I don't know how to go to the next key. I tried with enumerate(d)

but it pops up from AttributeError. I also tried d.iteritems().next()

but it goes into an infinite loop. Here is my code:

def output(d):
 a = 0
 keys = sorted(d.keys())
 while a <= 45:
  time = a + 15
  for k in keys:
   if time == k:
    sig = d[k]
   else:
    while time != k:
     k = d.iteritems().next()[0]
  print 'Time:', time, '-> Signal:' sig
  a += 1

      

        
        
        
      

    

Can anyone help me? Many thanks.

EDIT: For a better understanding, the expected output looks like this:

Time: 15s -> Signal: 001a
Time: 16s -> Signal: 001a
Time: 17s -> Signal: 001a
Time: 18s -> Signal: 001a
Time: 19s -> Signal: 001a
Time: 20s -> Signal: 111e
Time: 21s -> Signal: 111e
Time: 22s -> Signal: 111e 
Time: 23s -> Signal: 111e 
... 
Time: 31s -> Signal: 111e 
Time: 32s -> Signal: 8877
Time: 33s -> Signal: 8877
...
Time: 49s -> Signal: 8877
Time: 50s -> Signal: 00f3
Time: 51s -> Signal: 00f3
...
Time: 55s -> Signal: 00f3
Time: 56s -> Signal: 1000
Time: 57s -> Signal: 1000

      

        
        
        
      

    

... represents the time that is still running. This should show the data transition according to the text file above. Output signal reaches 60 seconds