proper use of list comprehensions - python

Question

Normally, list comprehensions are used to derive a new list from an existing list. Eg:

>>> a = [1, 2, 3, 4, 5]
>>> [i for i in a if i >          


        

Answer 1

Only use list comprehensions if you plan to use the created list. Otherwise you create it just for the GC to throw it again without ever being used.

So instead of [b.append(i) for i in a] you should use a proper for loop:

for i in a:
    b.append(i)

Another solution would be through a generator expression:

b += (i for i in a)

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However, if you want to append the whole list, you can simply do

b += a

And if you just need to apply a function to the elements before adding them to the list, you can always use map:

b += map(somefunc, a)