python numeric string comparison [duplicate]

问题

This question already has answers here:

How does Python 2 compare string and int? Why do lists compare as greater than numbers, and tuples greater than lists? (2 answers)

Ordering of string representations of integers [duplicate] (6 answers)

Closed 3 years ago.

I have numerical values that are loaded from a JSON object and are therefore all strings.

I am having issues with making numerical comparisons with these strings. The following makes no sense to me and I was hoping one of you champions could explain..

In[2]: print '100' < '45'
True

In[3]: print '99' < '45'
False

Using Python 2.7

回答1:

When comparing strings they're compared by the ascii value of the characters. '1' has a value 49, and '4' is 52. So '1' is < '4'. '9' however is 57, so '9' is > '4'.

If you want to compare them numerically you could just int() the strings first like:

print int('100') < int('45')

回答2:

It basically checks for lexicographic ordering. Check documentation here -

>>> 'b' <'a'
False
>>> 'a' < 'b'
True

In above example, a comes before b, hence 'a' <'b' is true. But, not vica versa. Similarly '1'<'2'. Hence '199999999999' < '5' is true because 1 comes before 5.

来源：https://stackoverflow.com/questions/35489619/python-numeric-string-comparison