具有 class 属性的列表理解

Question

I want to use class attributes to make a single list of all attributes:

from dataclasses import dataclass

@dataclass
class Foo:
    a: int
    b: int

data = [
    Foo(1,2),
    Foo(3,4)
]
print([[foo.a, foo.b] for foo in data])

But the result is a list of lists of attributes. How can I have a single list containing all attributes [1,2,3,4] instead of [[1,2],[3,4]] ?

Answer 1

I would recommend you to use itertools.chain.from_iterable to flatten the intermediate list

In [6]: import itertools

In [7]: print(list(itertools.chain.from_iterable([[foo.a, foo.b] for foo in data])))                                                                                                                               
[1, 2, 3, 4]

Answer 2

from functools import reduce 
from dataclasses import dataclass

@dataclass
class Foo:
  a: int
  b: int

data = [
  Foo(1,2),
  Foo(3,4)
]

result = [[foo.a, foo.b] for foo in data]
print(reduce(list.__add__, result))

Answer 3

Just use nested list comprehension

[x for x in [foo.a, foo.b] for foo in data]

Answer 4

You could do something like:

print([value for foo in data for attr, value in foo.__dict__.items()])

It's basically doing two for loops, the same as doing:

for foo in data:
    for attr, value in foo.__dict__.items():
        print(value)