How to find the number of lines of similar text in a file?

Question

Python

Need help
Let's say there are a lot of IDs in the file, and I need to calculate the number of my id from the file when I command, here is a small code example

with open('README.txt','r') as file:
file = file.read()
for i in file:
if str(message.from_user.id) in i:
#Here count the number of lines of your id.
bot.reply_to(message,text='and here is the output of the count from the file')

and most importantly, who did not understand, I need NOT to find out the number of lines FROM THE FILE, but FIND out how many lines ID FROM THE FILE