splitting lines, need to add element of same kind

[tester_V]

Hi,
I need to 'sum' all elements by their kind.
All dogs, cats, and fishes.
I Cannot wrap around my mind around this small task.
Here is a kind of file as an example:

line01,P,2,dog
line02,P,1,dog
line33,P,7,dog
line03,P,3,cat
line04,P,5,cat
line11,P,8,fish
line12,P,3,dog
line16,P,2,dog
line04,P,2,cat
line11,P,12,fish

I need to print out a number of Dogs, Cats, and fishes and replace the first line with a time stamp.
19/02/2021,P,15 dog
19/02/2021,P,10,cat
19/02/2021,P,20,fish
I scanned the file and made a list of the animals --- 'list'.
And I thought I would use the list to filter 'animals' by its kind and 'sum' them, for some reason it does not work.
Code:

from datetime import datetime

now = datetime.now()
date_time = now.strftime("%m/%d/%Y")
to_app ='C:/02/All_an.txt'

list = ['dog','cat','fish']

with open (to_app, 'r+') as app : 
    for ln_in_file in app :
        ln_in_file=ln_in_file.strip()

        for ech_element in list :
            Sum = 0
            if ech_element in ln_in_file :
                spel =ln_in_file.split(",")
                spel[2]=int(spel[2])
                print ("======================== ",spel[2])
                
                Sum=(spel[2]+spel[2])
                break
        print (Sum)  

I'm opening my file with 'r+' for some reason the file is not readable if I open it with 'append'
Thank you.