如何将 sys.argv 列表元素从字符串更改为整数？

Question

So I tried to convert a list of strings:

['25', '-36', '85', '94', '21', '-68', '-55', '24']

into a list of ints like:

[25, -36, 85, 94, 21, -68, -55, 24] 

So what I did is:

for i in range(len(sys.argv)):
    if isinstance(sys.argv[i], int) == True:
        sys.argv[i] = int(sys.argv[i])

But I'm not sure why the items in list are still strings...can someone explain?

Answer 1

Items in sys.argv are always string instances when the interpreter loads, so the test isinstance(sys.argv[i], int) would always return False .

To convert arguments into integers only if they represent integers, you can instead use a try-except block around the integer conversion to ignore strings that do not represent integers:

for i, s in enumerate(sys.argv):
    try:
        sys.argv[i] = int(s)
    except ValueError:
        pass

Answer 2

The reason why your code is not running is: it will never get into if statement .

if isinstance(sys.argv[i], int) will always return False since your input is a string. And your comparison isinstance(sys.argv[i], int) == True will always return False either, because you are always comparing False == True for any values in your initial string list.

---

The most easy and fast way to make your conversion is using list comprehension:

l_str = ['25', '-36', '85', '94', '21', '-68', '-55', '24']

l_int = [int(x) for x in l_str]