Why don't the strings turn into integers?

Question

L = [['1','2'], ['3,','4']]
for innerL in L:<br/>
    for item in innerL:
        item = int(item)

>>> print(L)
[['1','2'], ['3,','4']]

Why do the strings of numbers not change into integers? If I type:

>>> type(int('3'))
<class 'int'>

then shouldn't the item be turned into an integer? What am I missing?

Fundamentally, you are missing how Python variables work. Read the following: https://nedbatchelder.com/text/names.html — juanpa.arrivillaga, Dec 13 '17 at 23:12
You're just setting `item` to an int, you're not changing the values in the list. `L = [[int(digit) for digit in sub_list] for sub_list in L]` should work. — it's-yer-boy-chet, Dec 13 '17 at 23:13
You have a typo in your question I think. `'3,'`... the comma should be outside of the quotes. — roganjosh, Dec 13 '17 at 23:26

score 1 · Accepted Answer · answered Dec 13 '17 at 23:13

1

They are integers?

L = [['1','2'], ['3','4']]
for innerL in L:
  for item in innerL:
    item = int(item)
    print(item)
    print(isinstance(item, int))

Output:

1 True 2 True 3 True 4 True

answered Dec 13 '17 at 23:13

Caelan van Olm

score 0 · Answer 2 · answered Dec 13 '17 at 23:10

0

The name used is only a reference; if you want to change the sequence then you need to change it directly.

innerL[:] = [int(e) for e in innerL]

answered Dec 13 '17 at 23:10

Doesn't item in the for loop actually refer to the specific piece of data inside the list? If you type x = '3' then x = int(x), x will refer to 3. I'm still slightly confused. – SpaSmALX Dec 13 '17 at 23:27
@SpaSmALX: Long story short: "reference" doesn't mean the same thing in Python that it does in PHP and C++. – Ignacio Vazquez-Abrams Dec 14 '17 at 02:54

2 Answers2