Python - count instances without a specific line

Input file:

$ cat data.txt
k:begin:0
i:0:66
i:1:76
t:1:143
k:end:0
k:begin:7
i:0:55
i:1:65
i:2:57
k:end:7
k:begin:2
i:0:10
i:1:0
t:1:10
k:end:7
k:begin:2
i:0:46
t:0:46
k:end:7
k:begin:9
i:0:66
i:1:56
i:2:46
i:3:26
k:end:7

Required: Count total number of instances (one instance being from a 'k:begin' to 'k:end' line) which do not have a 't' line associated.

The python program:

import sys
count=0
data = open(sys.argv[1]).readlines()
for i in range(len(data)):
       if data[i].startswith("k:end") and data[i-1].split(":")[0]!="t":
               count=count+1
print count

Executing it:

$ python count_no_t.py data.txt
2

Related post:

- Print last instance of a file using Python
- Print line next to pattern in Python
- Print line above pattern in Python