"元组比较在 Python 中是如何工作的？"

Question

I have been reading the Core Python<\/em> programming book, and the author shows an example like:

(4, 5) < (3, 5) # Equals false

Answer 1

Tuples are compared position by position: the first item of the first tuple is compared to the first item of the second tuple; if they are not equal (ie the first is greater or smaller than the second) then that's the result of the comparison, else the second item is considered, then the third and so on.

See Common Sequence Operations :

Sequences of the same type also support comparisons. In particular, tuples and lists are compared lexicographically by comparing corresponding elements. This means that to compare equal, every element must compare equal and the two sequences must be of the same type and have the same length.

Also Value Comparisons for further details:

Lexicographical comparison between built-in collections works as follows:

• For two collections to compare equal, they must be of the same type, have the same length, and each pair of corresponding elements must compare equal (for example, [1,2] == (1,2) is false because the type is not the same).
• Collections that support order comparison are ordered the same as their first unequal elements (for example, [1,2,x] <= [1,2,y] has the same value as x <= y ). If a corresponding element does not exist, the shorter collection is ordered first (for example, [1,2] < [1,2,3] is true).

If not equal, the sequences are ordered the same as their first differing elements. For example, cmp([1,2,x], [1,2,y]) returns the same as cmp(x,y). If the corresponding element does not exist, the shorter sequence is considered smaller (for example, [1,2] < [1,2,3] returns True).

Note 1 : < and > do not mean "smaller than" and "greater than" but "is before" and "is after": so (0, 1) "is before" (1, 0).

Note 2 : tuples must not be considered as vectors in a n-dimensional space , compared according to their length.

Note 3 : referring to question https://stackoverflow.com/questions/36911617/python-2-tuple-comparison : do not think that a tuple is "greater" than another only if any element of the first is greater than the corresponding one in the second.

Answer 2

The Python documentation<\/a> does explain it.

Answer 3

I had some confusion before regarding integer comparsion, so I will explain it to be more beginner friendly with an example

a = ('A','B','C') # see it as the string "ABC" b = ('A','B','D')<\/code>

A is converted to its corresponding ASCII ord('A') #65<\/code> same for other elements

Answer 4

Comparing tuples

A comparison operator in Python can work with tuples. The comparison starts with a first element of each tuple. If they do not compare to = , < or > then it proceed to the second element and so on.

Let's study this with an example:

    #case 1
    a=(5,6)
    b=(1,4)
    if (a>b):print("a is bigger")
    else: print("b is bigger")

    #case 2
    a=(5,6)
    b=(5,4)
    if (a>b):print("a is bigger")
    else: print ("b is bigger")

    #case 3
    a=(5,6)
    b=(6,4)
    if (a>b):print("a is bigger")
    else: print("b is bigger")

Case1:

Comparison starts with a first element of each tuple. In this case 5>1, so the output a is bigger

Case 2:

Comparison starts with a first element of each tuple. In this case 5>5 which is inconclusive. So it proceeds to the next element. 6>4, so the output a is bigger

Case 3:

Comparison starts with a first element of each tuple. In this case 5>6 which is false. So it goes into the else loop prints "b is bigger."

conclusion:

Tuples always compare its first index and gives output according to your program. it does not compare all the elements.

Answer 5

The python 2.5 documentation<\/a> explains it well.