Parse list of strings and find max values

I'm quite new to Python and struggling to get my head round the logic in this for loop. My data has two values, a city and a temp. I would like to write a "for loop" that outputs the maximum temp for each city as follows:

PAR 31
LON 23
RIO 36
DUB 44

As it is to be used in Hadoop, I can't use any python libraries.

Here is my dataset:

['PAR,31',
 'PAR,18',
 'PAR,14',
 'PAR,18',
 'LON,12',
 'LON,13',
 'LON,9',
 'LON,23',
 'LON,5',
 'RIO,36',
 'RIO,33',
 'RIO,21',
 'RIO,25',
 'DUB,44',
 'DUB,42',
 'DUB,38',
 'DUB,34']

This is my code:

current_city = None
current_max = 0

for line in lines:
    (city, temp) = line.split(',')
   
    temp = int(temp)
    
    if city == current_city:
        if current_max < temp:
            current_max == temp

    current_city = city
            
print(current_city, current_max)

This was my output:

DUB 0

Build a dictionary keyed on city names. The associated values should be a list of integers (the temperatures).

Once the dictionary has been constructed you can then iterate over its items to determine the highest value in each list of temperatures,

data = ['PAR,31',
        'PAR,18',
        'PAR,14',
        'PAR,18',
        'LON,12',
        'LON,13',
        'LON,9',
        'LON,23',
        'LON,5',
        'RIO,36',
        'RIO,33',
        'RIO,21',
        'RIO,25',
        'DUB,44',
        'DUB,42',
        'DUB,38',
        'DUB,34']
d = {}
for e in data:
    city, temp = e.split(',')
    d.setdefault(city, []).append(temp)
for k, v in d.items():
    print(k, max(map(int, v)))

Output:

PAR 31
LON 23
RIO 36
DUB 44