Parsing the file in Python

Question

I have file in the following format:

Berlin, Germany 
New Delhi , India
New York , USA 
Mumbai , India
Seattle, USA

I need to parse the file and print the output as

Germany : Berlin
India: New Delhi , Mumbai 
USA:  New York, Seattle

I wrote a code:

enter code here:

def check():
    datafile=open('logfile.py','rU')
    found=False
    for line in datafile:
        if 'India' in line:
           lines=line.split()
           print("India"+":"+lines[0])
        if 'Germany' in line:
           lines=line.split()
           print("Germany"+":"+lines[0])
        if 'USA' in line:
           lines=line.split()
           print("USA"+":"+lines[0])
    datafile.close()
check()

This code is giving output as:

Germany:Berlin
India:NewDelhi
USA:NewYork
India:Mumbai
USA:Seattle

Please help.

How are you doing a default split() and losing the commas? — TigerhawkT3
– TigerhawkT3, Commented Apr 20, 2016 at 21:22
Essentially, as you can see in the first answer, you'll have to make lists for all countries. So the trick is to start a country list, then decide whether a country already exists or not, then append the city to the country list. — roadrunner66
– roadrunner66, Commented Apr 20, 2016 at 21:28
@roadrunner66 - collections.defaultdict manages all of that for you — PaulMcG
– PaulMcG, Commented Apr 20, 2016 at 22:12

idjaw · Accepted Answer · 2016-04-20 21:31:17Z

4

Another approach, is using defaultdict from collections to achieve this:

from collections import defaultdict

def check():
    d = defaultdict(list)
    with open('logfile.py', 'rU') as datafile:
        for line in datafile:
            data = line.split(',')
            d[data[1].strip()].append(data[0].strip())
    return d
res = check()

for k, v in res.items():
    print("{} : {}".format(k, ', '.join(v)))

Output:

India : New Delhi, Mumbai
Germany : Berlin
USA : New York, Seattle

answered Apr 20, 2016 at 21:31

idjaw

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1 Comment

Jongware Over a year ago

Nice – now it makes me wonder how to get that irrational spacing in the original 'required' list.

TigerhawkT3 · Accepted Answer · 2016-04-20 21:34:38Z

Instead of directly printing everything, you could save it to a data structure like a dictionary or collections.defaultdict.

import collections.defaultdict as dd
result = dd(list)
with open('logfile.py', 'rU') as datafile:
    for line in datafile:
        city,country = map(str.strip, line.strip().split(','))
        result[country].append(city)

Then print your results:

for country in result:
    print(country+':', ', '.join(result[country]))

If you think there may be duplicate country/city listings and you don't want them, use set and add instead of list and append.

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