python中有什么方法可以从字典列表中获取特定的值列表？

Question

I have a variable and list imported from excel that looks like below:

cities= [{'City': 'Buenos Aires',
  'Country': 'Argentina',
  'Population': 2891000,
  'Area': 4758},
 {'City': 'Toronto',
  'Country': 'Canada',
  'Population': 2800000,
  'Area': 2731571},
 {'City': 'Pyeongchang',
  'Country': 'South Korea',
  'Population': 2581000,
  'Area': 3194},
 {'City': 'Marakesh', 'Country': 'Morocco', 'Population': 928850, 'Area': 200},
 {'City': 'Albuquerque',
  'Country': 'New Mexico',
  'Population': 559277,
  'Area': 491},
 {'City': 'Los Cabos',
  'Country': 'Mexico',
  'Population': 287651,
  'Area': 3750},
 {'City': 'Greenville', 'Country': 'USA', 'Population': 84554, 'Area': 68},
 {'City': 'Archipelago Sea',
  'Country': 'Finland',
  'Population': 60000,
  'Area': 8300},
 {'City': 'Walla Walla Valley',
  'Country': 'USA',
  'Population': 32237,
  'Area': 33},
 {'City': 'Salina Island', 'Country': 'Italy', 'Population': 4000, 'Area': 27},
 {'City': 'Solta', 'Country': 'Croatia', 'Population': 1700, 'Area': 59},
 {'City': 'Iguazu Falls',
  'Country': 'Argentina',
  'Population': 0,
  'Area': 672}]

I just want the value 'Population' from each cities. What is the most efficient or easiest way to make a list with value from each cities 'Population'?

Below is the code that I came up with, but it's inefficient.

City_Population = [cities[0]['Population'], cities[1]['Population'], cities[2]['Population']]

I am currently learning Python and any advice would be helpful!

Thank you!

Answer 1

Using list comprehension:

print([city['Population'] for city in cities])

OUTPUT :

[2891000, 2800000, 2581000, 928850, 559277, 287651, 84554, 60000, 32237, 4000, 1700, 0]

EDIT :

Assuming there is no population in a city :

print([city['Population'] for city in cities if 'Population' in city])

OUTPUT (removed population from a few cities in the list):

[2891000, 2800000, 2581000, 928850, 287651, 84554, 32237, 4000]

Answer 2

Use a getter, that way you will have empty/none values if some of them are not defined.

populations = [city.get('Population') for city in cities]

If you don't want the empty values:

populations = [pop for pop in populations if pop is not None]