CODEWITHSUNDEEP
pythonmax
YoungDanEn
YoungDanEn

Reputation: 27

confused about max() built in function

hello I am kind of confused about the max() function, I have the following code:

a = '9:30'
b = '10:44'
c = '8:22'
x = max(a, b, c)
print (x)

so my question is: why does this return 9:30? and if I were to delete the a from inside max it would return 8:22

Upvotes: 2

Views: 1506

Answers (7)

Tanveer Alam
Tanveer Alam

Reputation: 5275

As you are doing string comparison the int or ASCII value of '9' is greater than '8' and '1'. You can see the int value of individual char using ord built-in function.

>>> ord('9')
57
>>> ord('1')
49
>>> ord('8')
56

And as Python does comparison in lexicographical manner(from left to right each char). It finds value of '9' greater. And if you delete '9' if finds '8''s value greater than '1'.

One way to achieve could be :-

a = '9:30'
b = '10:44'
c = '8:22'
d = '10:55'

print max([a, b, c, d], key=lambda x: map(int, x.split(':')))

Upvotes: 2

user4237459
user4237459

Reputation:

Here's another way to do it so you can just use the regular max function. First, pad the strings so that "9" becomes "09" and "10" stays "10". You can use str.zfill for this:

a = '9:30'
b = '10:44'
c = '8:22'
a, b, c = map(lambda s: s.zfill(5), (a, b, c))

Now, they will be what you want lexicographically!

print(max([a, b, c]))
10:44

You only have to pad them once, but you will be stuck with:

print(min([a, b, c]))
08:22

Upvotes: 0

Kasravnd
Kasravnd

Reputation: 107287

Its because of that max function will find the max value lexicographicaly , you can use a proper key for max function to convert the hour and min to int.

>>> l=[a,b,c]
>>> max(l,key=lambda d :map(int, d.split(":")))
'10:44'

Upvotes: 1

tobias_k
tobias_k

Reputation: 82899

You are comparing strings, not numbers or times. As such, it compares the strings by their first character (and if those are equal, by the second, and so on), and the first character of "9:30" is the highest.

If you want to compare the times, you can split the string at the :symbol, map the parts to integers and compare those, using an according key function.

x = max([a, b, c], key=lambda s: map(int, s.split(":")))

Upvotes: 0

Matthew
Matthew

Reputation: 658

it is comparing strings, and, as such, it starts by comparing the first character, and then, if that character is the same, moves on to the next and then the next etc etc.

So '9:30' is returned because 9 > 8 > 1. If you want "10:44" to return, then you should use the datetime module, unless you want to write custom code for that

edit: and sniped by people who type faster!

Upvotes: 0

Craig Burgler
Craig Burgler

Reputation: 1779

Since it's arguments are strings, it is returning the string that is latest in alphabetic order.

Upvotes: 0

Simeon Visser
Simeon Visser

Reputation: 122376

String a compares as the biggest because it starts with 9 and the other strings start with 1 and 8. Python therefore returns '9:30' as the maximum value out of those three strings.

Upvotes: 5

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