I am trying to append numbers from a generator to an empty list using a single line for loop but it returns None. I understand it can be done using a for loop with 2 lines but I was wondering what I am missing. i.e.,
>>> [].append(i) for i in range(10)
[None, None, None, None, None, None, None, None, None, None]
I was hoping to create this in one line:
>>> [].append(i) for i in range(10)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
Thank you.
Write a proper comprehension, without append.
>>> [i for i in range(10)]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> list(i for i in range(10))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
Adding Explanation as to what happens, Append doesn't return anything,
y = []
x = [y.append(i) for i in range(10)]
print(x)
print(y)
produces
[None, None, None, None, None, None, None, None, None, None]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[Program finished]
you can also just cast a range which is a iterable:
list(range(10))
>>> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
also for numpy users:
np.arange(10)
>>> array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
or you can use linspace if its more understandable to you (linspace(from,to,pieces)) :
np.linspace(0,9,10)
>>> array([0., 1., 2., 3., 4., 5., 6., 7., 8., 9.])
y = []
[y.append(i) for i in range(10)]
print(y)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
