Python one-line “for” expression

问题:

I'm not sure if I need a lambda, or something else. But still, I need the following:

I have an array = [1,2,3,4,5]. I need to put this array, for instance, into another array. But write it all in one line.

for item in array:
    array2.append(item)

I know that this is completely possible to iterate through the items and make it one-line. But googling and reading manuals didn't help me that much... if you can just give me a hint or name this thing so that I could find what that is, I would really appreciate it.

Update: let's say this: array2 = SOME FANCY EXPRESSION THAT IS GOING TO GET ALL THE DATA FROM THE FIRST ONE

(the example is NOT real. I'm just trying to iterate through different chunks of data, but that's the best I could come up with)

回答1:

The keyword you're looking for is list comprehensions:

>>> x = [1, 2, 3, 4, 5]
>>> y = [2*a for a in x if a % 2 == 1]
>>> print(y)
[2, 6, 10]

回答2:

for item in array: array2.append (item)

Or, in this case:

array2 += array

回答3:

If you're trying to copy the array:

array2 = array[:]

回答4:

If you really only need to add the items in one array to another, the '+' operator is already overloaded to do that, incidentally:

a1 = [1,2,3,4,5]
a2 = [6,7,8,9]
a1 + a2
--> [1, 2, 3, 4, 5, 6, 7, 8, 9]

回答5:

Even array2.extend(array1) will work.

回答6:

Using elements from the list 'A' create a new list 'B' with elements, which are less than 10

Option 1:

A = [1, 1, 2, 3, 5, 8, 13, 4, 21, 34, 9, 55, 89]

B = []
for i in range(len(A)):
    if A[i] < 10:
        B.append(A[i])
print(B)

Option 2:

A = [1, 1, 2, 3, 5, 8, 13, 4, 21, 34, 9, 55, 89]

B = [A[i] for i in range(len(A)) if A[i] < 10]
print(B)

Result: [1, 1, 2, 3, 5, 8, 4, 9]