filename = 'cats_of_ulthar.txt'
import re
word = 'кошка'
launches = []
with open(filename, encoding='utf-8') as file:
    for line in file: launches.append(line.split(','))
print(len(re.findall('word[а-яА-Я]+', filename)))

 import re
tmp = re.compile("кошка")
with open("cats_of_ulthar.txt", encoding="utf-8") as f:
    res = tmp.findall(f.read())
print(len(res))

  
>>> import re
>>> 
>>> pat = (r'\b(кошка|кошки|кошке|кошку|кошкой'
...        r'кошки|кошек|кошкам|кошках|кошками)\b')
>>> 
>>> with open('file.txt', encoding='utf-8') as fin:
...     n = 0
...     for line in fin:
...         found = re.findall(pat, line)
...         if found:
...             print(found)
...             n += len(found)
...     print(n)
... 
['кошку']
['кошка']
['кошка']
['кошек']
['кошек']
['кошки']
['кошку']
['кошек']
['кошек']
['кошка']
['кошек']
['кошек']
['кошки']
['кошек']
['кошкам']
['кошки']
['кошек']
['кошка']
['кошки']
['кошек', 'кошка']
['кошек']
['кошки']
['кошки']
['кошку']
25
>>>