Flatten a list of lists containing single strings to a list of ints

You can simply do this:

allyears = [int(i[0]) for i in allyears]

Because all the elements in your allyears is a list which has ony one element, so I get it by i[0]

The error is because ypu can't convert a list to an int

You're very close, you just need to take the first (and only) element of allyears[i] before doing the int conversion:

for i in range(0, len(allyears)): 
    allyears[i] = int(allyears[i][0]) 

Alternatively, you could do this in one line using a list comprehension:

allyears = [int(l[0]) for l in allyears]

if you want a simple for loop you also may use enumerate built-in function and unpack your inner list:

for i, [n] in  enumerate(allyears): 
    allyears[i] = int(n) 

you can use a list comprehension:

allyears = [int(e) for l in allyears for e in l]

also, you can use itertools.chain

from itertools import chain

list(map(int, chain.from_iterable(allyears)))

output:

[1916, 1919, 1922, 1912, 1924, 1920]

the last 2 solutions will work also if in your inner lists you have more than one element

You need to access individual elements of the list instead of lists itself.

Try:

for i in range(0, len(allyears)): 
    allyears[i] = int(allyears[i][0]) 

Try:

allyears = [['1916'], ['1919'], ['1922'], ['1912'], ['1924'], ['1920']]

out = []
for i in range(0, len(allyears)): 
    out.append(int(allyears[i][0]))

print (out)

You tried this:

for i in range(0, len(allyears)): 
    allyears[i] = int(allyears[i]) 

and got the error

TypeError: int() argument must be a string, a bytes-like object or a number, not 'list'

The next thing you should have tried is:

for i in range(0, len(allyears)): 
    print(allyears[i])

And you would have seen that you are looping through these values:

['1916']
['1919']
['1922']

etc.

Those cannot be converted to int using int(), because those are lists. You should get the only element of those lists using the [0] index like this:

>>> for i in range(0, len(allyears)): 
...    print(allyears[i][0])
1916
1919
1922...

And now you know how to correct your original code:

for i in range(0, len(allyears)): 
    allyears[i] = int(allyears[i][0])

The more Pythonic solution to your problem would use list comprehension:

allyears = [int(i[0]) for i in allyears]