Data and signal extraction from a file

Question

before I begin, I'm just a beginner at here as well as in Python and I am working on something like data extraction from a file and then from the data I need to produce a signal of the data. I don't know how to explain it exactly but I will try my best to explain the problem and here goes. 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 relates to the text file, where the first column represents time and the second column represents the data. It means like at time = 15s, the data is 001a up till time = 20s, where the data changes to 111e. The data continues the same (111e) up till time = 32s, where the data changes to 8877 again. Same process goes on. I was required to extract the output produced from time = 15s to time = 60s in the interval of 1s within the time. The problem is I don't know the exact method to do this part. I don't know how to go to next key for this. I have tried with enumerate(d) but it keeps pop out AttributeError. I also tried d.iteritems().next() but it goes to infinite loop. Here goes 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? Thanks a lot.

EDIT: For better understanding, the expected output is as below:

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 still runs. This is to show the transition of the data according to the text file above. The output runs up to 60s

Answer 1

Assuming your file as signals.txt

def read_signal(filename):
    with open(filename) as fh1:
        d = {}
        for line in fh1:
            (t, s) = line.split()
            d[int(t)] = s
        for i in range(15,61):
            if i in sorted(d):
                j = d[i]
            print ("Time: " + str(i) + "s -> Signal: " + j)
read_signal("signals.txt")