Iterate over multiple files and count multiple strings

I want to write a code to open multiple text files and count how many times predefined strings occurs in each file. My desired output it can be a list of the sums of occurrence of each string along the files.

My desired strings are values of a dictionary.

For instance:

mi = { "key1": "string1", "key2": "string2", and so on..." }

For the purpose to open a unique file and realized my desired count I got the code. Check below:

mi = {} #my dictionary
data = open("test.txt", "r").read()
import collections 
od_mi = collections.OrderedDict(sorted(mi.items()))
count_occur = list()

for value in od_mi.values():
    count = data.count(value)
    count_occur.append(count)

lista_keys = []   
for key in od_mi.keys():
    lista_keys.append(key)

dic_final = dict(zip(lista_keys, count_occur))
od_mi_final = collections.OrderedDict(sorted(dic_final.items()))

print(od_mi_final) #A final dictionary with keys and values with the count of how many times each string occur. 

My next target is do the same with multiple files. I have a group of text files that are named according a pattern, e.g. "ABC 01.2015.txt ; ABC 02.2015.txt ...".

I made 3 text files as test files, in each one of the files, each string occurs one time. Therefore, in my test run my desired output is a count of 3 for each string.

mi = {}
import collections
od_mi = collections.OrderedDict(sorted(mi.items()))
for i in range(2,5):
for value in od_mi.values():
    x = "ABC" + " " + str(i) +".2015.txt"
    data = open(x, "r").read()
    contar = data.count(value)
    count_occur.append(contar)

 print(count_occur)

Output:

[1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1]

I realize that my code was overwriting the counting when entered each time in the loop. Therefore, how can I fix this issue?