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.

• TigerhawkT3: How are you doing a default split() and losing the commas?
• roadrunner66: 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.
• PaulMcG: @roadrunner66 - collections.defaultdict manages all of that for you
• roadrunner66: @PaulMcGuire Ty :)

Answer 1

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

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

Answer 2

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.