如何在Python中将字符串中的数字引用转换为整数？

Question

I have a series of text files that include numerical references. I have word tokenized them and I would like to be able to identify where tokens are numbers and convert them to integer format.

mysent = ['i','am','10','today']

I am unsure how to proceed given the immutability of strings.

Answer 1

请尝试[item if not item.isdigit() else int(item) for item in mysent]尝试[item if not item.isdigit() else int(item) for item in mysent]

Answer 2

If you try to convert a string that is not a representation of an int to an int , you get a ValueError .

You can try to convert all the elements to int , and catch ValueError s:

mysent = ['i','am','10','today']

for i in mysent:
    try:
        print(int(i))
    except ValueError:
        continue

OUTPUT:

10

If you want to directly modify the int inside mysent , you can use:

mysent = ['i','am','10','today']

for n, i in enumerate(mysent):
    try:
        mysent[n] = int(i)
    except ValueError:
        continue

print(mysent)

OUTPUT:

['i', 'am', 10, 'today']

.isdigit() IS NOT THE SAME AS try/except!!!!

In the comments has been pointed out that .isdigit() may be more elegant and obvious. As stated in the Zen of Python , There should be one-- and preferably only one --obvious way to do it .

From the official documentation , .isdigit() Return true if all characters in the string are digits and there is at least one character, false otherwise.

Meanwhile, the try/except block catches the ValueError raised by applying int to a non-numerical string .

They may look similar, but their behavior is really different:

def is_int(n):
    try:
        int(n)
        return True
    except ValueError:
        return False

EXAMPLES:

Positive integer:

n = "42"

print(is_int(n))   --> True
print(n.isdigit()) --> True

Positive float:

n = "3.14"

print(is_int(n))   --> False
print(n.isdigit()) --> False

Negative integer:

n = "-10"

print(is_int(n))   --> True
print(n.isdigit()) --> False

u hex:

n = "\u00B23455"

print(is_int(n))   --> False
print(n.isdigit()) --> True

These are only some example, and probably you can already tell which one suits better your needs.
The discussion open around which one should be used is exhausting and neverending, you can have a look a this couple of interesting SO QA:

• try/except comparsion
• input validation analysis