Python のリストを宣言します： 構文と例

my_list = []

my_list = list()

matrix = [ [], [] ]

rows = 3
cols = 4
 
my_list = []
for _ in range(rows):
    inner_list = []
    for _ in range(cols):
        inner_list.append(None)
    my_list.append(inner_list)

rows = 3
cols = 4
 
my_list = [[None for _ in range(cols)] for _ in range(rows)]
 
# Output
[
    [None, None, None, None],
    [None, None, None, None],
    [None, None, None, None]
]

list_count = 5
list_5 = [ 0 for _ in range(list_count) ]
 
# output
[0, 0, 0, 0, 0]

list_count = 5
list_5_a = [ 'a' for _ in range(list_count) ]
 
# output
['a', 'a', 'a', 'a', 'a']

row = 4
col = 3
 
matrix = [ [chr(97 + i + j) for i in range(col)]  for j in range(row)]
 
# output
[['a', 'b', 'c'],
 ['b', 'c', 'd'],
 ['c', 'd', 'e'],
 ['d', 'e', 'f']]

class Student:
    def __init__(self, age):
        self.age = age
 
    def __repr__(self):
        return f'Student(age:{self.age})'
 
    def __str__(self):
        return f'Student(age:{self.age})'
 
list_count = 5
matrix  = [ Student(age) for age in range(list_count) ]
 
# output
[Student(age:0), Student(age:1), Student(age:2), Student(age:3), Student(age:4)]

# init as global
my_list = []
 
def add_to_list(value):
    global my_list
    my_list.append(value)
 
add_to_list(1)
add_to_list(2)
print(my_list)
 
# Output: [1, 2]