How to count certain lines in a file?

Question

There is I file and I need to count the certain lines in it, not the all lines, is there an opportunity to do it. Because the only way to count lines that I have found is:
a = open("my_file.txt")
count=0
for line in a:
count = count +1
print (count)
But it counts all lines, and when I extract the certain lines I want to count and use this code it counts only characters in one line 🤔

Answer 1

def count_char(text):
count = 0
for c in text:
count += 1
return count

This is for charecter count..
So passing the line as argument gives charecters in certain line..
For line in a:
print(char_count(line)

Hoping it helps,.. For some info about see the text analylzer topic from this..
https://www.sololearn.com/learn/JUMP_LINK__&&__Python__&&__JUMP_LINK/2457/