Convert List of numbers as string to a single Integer-CodePudding

I'm trying to convert a list to a single integer using two methods:

for loop works fine and gives me the integer

>>> a_list = "123456789"
>>> a_list = list(a_list)
>>> b_int = ""
>>> for num in a_list:
    ... b_int  = num
    ...
>>> print(int(b_int))

123456789

however join() returns a ValueError

>>> a_list = "123456789"
>>> c_int = ""
>>> c_int.join(a_list)
>>> print(int(c_int))

Traceback (most recent call last):
  File "xxx.py", line 4, in <module>
    print(int(c_int))
          ^^^^^^^^^^
ValueError: invalid literal for int() with base 10: ''

Why does join() returns a ValueError? It was suggested in a number of different posts as a better solution.

CodePudding user response：

As the string is a string it cannot be "joined" to a number, but if the string contains numbers it can be cast to numbers and then reduced

list("123456789")
Out[6]: ['1', '2', '3', '4', '5', '6', '7', '8', '9']
[int(x) for x in list("123456789")]
Out[7]: [1, 2, 3, 4, 5, 6, 7, 8, 9]
sum([int(x) for x in list("123456789")])
Out[8]: 45

CodePudding user response：

The origin of the ValueError is that you are calling int to an empty string and not to the join one. String are immutables so you need always to re-assign the result.

a_list = "123456789"
c_int = ""
c_int = c_int.join(a_list) # <- 

print(int(c_int))

By the way int(a_list) does the same.