gistfile1.py

from collections import OrderedDict

input = [{
    'name': 'Product1',
    'locations': ['Paris', 'London', 'Ljubljana']
}, {
    'name': 'Product2',
    'locations': ['Berlin', 'London', 'New York']
}]

# try to atleast obtain some order, otherwise normal dict is just fine
locations = OrderedDict()
for product in input:
    for location in product['locations']:
        if location not in locations:
            locations[location] = []

        locations[location].append(product['name'])

output = [{'location': location, 'products': products} for location, products in locations.items()]
print(output)

"""
[{
    'products': ['Product1'], 
    'location': 'Paris'
}, 
{
    'products': ['Product1', 'Product2'], 
    'location': 'London'
}, 
{
    'products': ['Product1'], 
    'location': 'Ljubljana'
}, 
{
    'products': ['Product2'], 
    'location': 'Berlin'
}, 
{
    'products': ['Product2'], 
    'location': 'New York'
}]
"""