字符串比较同时包含数字和字母时如何工作？

Question

I'm trying to compare time in Python, and came up with some weird comparisons. I've got no idea how the following statements work:

>>> "17:30" > "16:30"
True
>>> "12:30" > "13:30"
False
>>> '18:00 - asdfj' > '16:30 - asdfj'
True

My guess is that it takes the first number from before the colon, I'm not completely sure about it.

Answer 1

Basically, in python, it is lexicographical comparison.

Example 'a' comes before 'b', hence 'a' < 'b' is true. Similarly '2' < '3'. Hence '199' < '2' is true because 1 comes before 2.

Answer 2

As others have pointed out, a comparison between strings is a question of lexicographical ordering.

What that means procedurally:

• two strings are compared one character at a time
• the first character that's different decides which string is 'greater than' the other
• if no characters are different and the strings are the same length, they are 'equal'.
• if two characters are different, their 'ordinal value' decides which is 'greater'
• a character is 'greater than' no character

For example, 'ab' > 'a' is True , because 'a' == 'a' , but the first string has an extra character. And 'abc' < 'abd' because 'c' < 'd' .

'a' < 'b' because ord('a') < ord('b') . The ordinal value of a character is typically its ASCII value for normal characters, or more precisely, its the Unicode code point ( https://docs.python.org/3/library/functions.html#ord ). This also means that 'A' < 'a' , because uppercase letters come before lowercase letters in Unicode. And '1' < 'A' because numbers come before letters.

Note that this may sometimes give surprising results (note the dots on the Ӓ ):

>>> 'Ӓ' > 'a'
True
>>> 'A' > 'a'
False

There are many online tables and overviews of Unicode, but here's a fairly plain example: https://www.tamasoft.co.jp/en/general-info/unicode.html

As for your example:

>>> '18:00 - asdfj' > '16:30 - asdfj'
True

This makes sense, because '8' > '6' - the rest of the string doesn't matter.