Python 2.x gotchas and landmines

Question

The purpose of my question is to strengthen my knowledge base with Python and get a better picture of it, which includes knowing its faults and surprises. To keep things sp

Answer 1

If you create a list of list this way:

arr = [[2]] * 5 
print arr 
[[2], [2], [2], [2], [2]]

Then this creates an array with all elements pointing to the same object ! This might create a real confusion. Consider this:

arr[0][0] = 5

then if you print arr

print arr
[[5], [5], [5], [5], [5]]

The proper way of initializing the array is for example with a list comprehension:

arr = [[2] for _ in range(5)]

arr[0][0] = 5

print arr

[[5], [2], [2], [2], [2]]