Python array column inserting

Question

i was working with arrays in python and i wanted to insert one array as column in 2d array and i see that for some reason my column is filled with only last element of words[]

words = ['first','second','third','fourth','fifth']
tab = [[None]*5]*len(words)
for i in range(len(words)):
    tab[i][0] = words[i]
for i in range(len(words)):
    print(tab[i])


#output
['fifth', None, None, None, None]
['fifth', None, None, None, None]
['fifth', None, None, None, None]
['fifth', None, None, None, None]
['fifth', None, None, None, None]

What is your expected output? – Edward Edberg Oct 08 '20 at 10:25 — Edward Edberg, Oct 08 '20 at 10:25

score 1 · Answer 1 · answered Oct 08 '20 at 10:27

1

youre copying values using

[None]*5

and

*len(words)

your need:

words = ['first','second','third','fourth','fifth']
tab = [[[None] for i in range(5)] for i in range(len(words))]
for i in range(len(words)):
    tab[i][0] = words[i]
for i in range(len(words)):
    print(tab[I])

outs

['first', [None], [None], [None], [None]]
['second', [None], [None], [None], [None]]
['third', [None], [None], [None], [None]]
['fourth', [None], [None], [None], [None]]
['fifth', [None], [None], [None], [None]]
>>>

answered Oct 08 '20 at 10:27

Timur U

415
2
14

thanks, but i dont understand how we get this :D i its something like string pools? – Secane Oct 08 '20 at 10:30
[[None] for i in range(5)] means 5 steps [None]: [[None],[None],[None],[None],[None]] – Timur U Oct 08 '20 at 10:34
when your use : '[[None]*5]*len(words)', main problem with: '*len(words)' your only copying its, and change itch of is your change all of this – Timur U Oct 08 '20 at 10:38
So the reference is also "cloned" – Secane Oct 08 '20 at 10:39
yes you're right! its cloning )) – Timur U Oct 08 '20 at 10:44
`[[Value] for i in range(5)]` - making `range(5)` **different** values – Timur U Oct 08 '20 at 10:45

Python array column inserting

1 Answers1