在python或空数组中创建多个列表

Question

Hello I'm Just searching for a way to create multiple lists at once. by that I mean.

day1 = []
day2 = []
up to 7 days....
day7 = []

instead of having to copy and paste all the time and make my code look unprofessional and not looking good. I wanted to create a loop that creates these lists automatically.

Answer 1

Here are a couple of options:

1. A basic list comprehension:

seven_lists = [[] for i in range(7)]

Which gives a nested list of seven lists:

[[], [], [], [], [], [], []]

2. A list of (day, []) tuples:

days = [("day " + str(i+1), []) for i in range(7)]

Which gives:

[('day 1', []), ('day 2', []), ('day 3', []), ('day 4', []), ('day 5', []), ('day 6', []), ('day 7', [])]

3. A dictionary of days:

days = {"day " + str(i+1) : [] for i in range(7)}

Which gives:

{'day 1': [], 'day 2': [], 'day 3': [], 'day 4': [], 'day 5': [], 'day 6': [], 'day 7': []}

And then you can access/update each/multiple days like this:

>>> days['day 1']
[]
>>> days['day 1'].append(1)
>>> days['day 1']
[1]
>>> days
{'day 1': [1], 'day 2': [], 'day 3': [], 'day 4': [], 'day 5': [], 'day 6': [], 'day 7': []}
>>> days.update({'day 2': [1, 2, 3]})
>>> days
{'day 1': [1], 'day 2': [1, 2, 3], 'day 3': [], 'day 4': [], 'day 5': [], 'day 6': [], 'day 7': []}

Answer 2

you can use dict

dct = {}
for i in range(1,8):
   dct["day"+str(i)] = []

or dict comprehensions

dct = { 'day'+str(i):[] for i in range(1,8) }

output:

{'day6': [], 'day7': [], 'day4': [], 'day5': [], 'day2': [], 'day3': [], 'day1': []}

Answer 3

我能想到的最短的方法就是这个。

day1, day2, day3, day4, day5, day6, day7 = [], [], [], [], [], [], []

Answer 4

An odd way that is sometimes worthwhile is

from collections import defaultdict
days = defaultdict(list)
print(days['day1']) #prints [], 

Doing this you can use whatever you like for day of week keys as long as you are consistent. Like

days['Monday']

or use number keys to make it look like an array.