I am new to Python and have a problem with lists. Namely, I'm asking user to fill 2 lists one for cars and one for the production year. Then I append both list to one.
enter code here
carYear = []
carYear.append(cars)
carYear.append(year)
I have 2 questions: a) is there an elegant way to print those lists, so the element car and year are listed close to each other (for ex: Porsche, 1998)? b) Is it possible to access first list (cars) from carYear list and print it?
You can zip the two lists together like so:
cars = ["car1", "car2", "car3"]
years = ["2012", "2015", "2017"]
for c, y in zip(cars, years):
print( "{0}, {1}".format(c, y) )
For each iteration you can print c and y. Which is the name and the year of the car.
I suggest changing your data structure to use a dict instead of parallel list objects. Dictionaries (dict) are sometimes referred to as maps or associative arrays. They allow you to access data by associating it with a key value. The following example assumes that the elements of cars will serve as keys.
You can create a dictionary from your lists using zip, which transforms the given sequences into tuples.
>>> cars = ['civic', 'corvette', 'prius']
>>> years = ['2009', '1979', '2017']
>>> zip(cars, years)
[('civic', '2009'), ('corvette', '1979'), ('prius', '2017')]
A list of tuples can be used to initialize a dict where first and second elements of each tuple are the key and value, respectively.
>>> carYear = dict(zip(cars, years))
>>> carYear
{'corvette': '1979', 'prius': '2017', 'civic': '2009'}
Now, you can do this:
>>> carYear['corvette']
'1979'
For printing the contents of dict objects, I like to use the .items() method which breaks things apart into tuples again. Observe:
for car, year in sorted(carYear.items()):
print('Car: {} => {}'.format(car, year))
I am using sorted to ensure that output is consistent. Due to the implementation of dict objects, .items() will return data in random order each time you run. sorted addresses this problem, resulting in consistent output.
For more information about Python dictionaries see the Python docs here: https://docs.python.org/3/tutorial/datastructures.html#dictionaries
You can try namedtuple (It should be faster than dict) e.g:
from collections import namedtuple
cars = []
Car = namedtuple('Car', ['type', 'year'])
cars.append(Car('Porsche', '1998'))
for car in cars:
print('{0}, {1}'.format(car.type, car.year))
But be aware, namedtuples are immutable. i.e. you cannot do car.type = 'BMW'
