difference between forms of input a list to function

[snippsat]

The be more accurate when do f(b[:] you are making a copy of b then pass if to f.
func-1 you're passing the reference of the list,so the function modifies the original list.
func-2 you're passing a shallow copy of the list to the function,so the original list remains unchanged.

To give an other example,which also is a common mistake(modify a list you loop over) why is albatross in output?

words = ['eagle', 'albatross', 'mouse', 'dog', 'tiger']
for w in words:
    if len(w) > 3:
        words.remove(w)

print(words)

Output:
['albatross', 'dog']

If loop over copy of words then it work.

words = ['eagle', 'albatross', 'mouse', 'dog', 'tiger']
for w in words[:]:
    if len(w) > 3:
        words.remove(w)

print(words)

Output:
['dog']

Or better do not use copy or remove at all.

words = ['eagle', 'albatross', 'mouse', 'dog', 'tiger']
words = [w for w in words if len(w) <= 3]
print(words)

Output:
['dog']