I am trying to initiliase a list with the first 5 elements empty and then append to the list thereafter. The purpose is that when i write this list to a csv file, the output will be as such: ,,,,,,a,b,c here is my code:
l = list()
l[:5]=""
l.append('a')
When i print out this list, it contains only the element 'a'. How can I initiliase the list such the first 5 elements are empty and when I print it out it will show something like [, , , , , 'a']
thanks
For immutable types like string you can do -
lst = [""] * 5
Though doing this for mutable elements (like lists or so) can cause issues as all the five elements would be pointing to the same object , so mutating one of them would cause changes reflected in the other elements (as they are the same object) .
Use None type.
>>> lst = [None] * 5
>>> lst.append("a")
>>> lst
[None, None, None, None, None, 'a']
If you do [ [] ] * 10 the pointer will be copied to all items:
>>> a = [[]] * 10
>>> a
[[], [], [], [], [], [], [], [], [], []]
>>> b = [ [] for i in range(10) ]
>>> b
[[], [], [], [], [], [], [], [], [], []]
>>> a[0].append(5)
>>> a
[[5], [5], [5], [5], [5], [5], [5], [5], [5], [5]]
>>> b[0].append(5)
>>> b
[[5], [], [], [], [], [], [], [], [], []]
You can do:
l = [''] * 5
l.append('a')
print l
Remember that you can:
multiply lists to repeat them (e.g. [1, 2] * 2 = [1, 2, 1, 2])
add lists together (e.g. [1, 2] + [3, 4] = [1, 2, 3, 4])
Here is a suggested structure:
a = 'new item'
l = [''] * 5 + a
>>> l
['', '', '', '', '', 'new item']
