CODEWITHSUNDEEP
pythonstringslice
J4102
J4102

Reputation: 473

Slice From Length to Beginning Index

When slicing a string, I know that the notation is [start:stop:counter]. If that's the case though, if I have string = "hello", why does string[5:0:-1] return olleinstead of olleh? string[::-1] returns olleh for me so that is fine but I am confused on why the first syntax does not work

Upvotes: 4

Views: 522

Answers (4)

Red
Red

Reputation: 27577

As you can see,index 5 is out of range:

string = "hello"
#         01234
print(string[5:0:-1])

But that's okay, python will handle it by ignoring it.

Like:

print(string[100:0:-1])

Output:

olle

You know that in slices like string[0, 3], it will return 'hel' (the index 3 is not included), so same goes for backward slicing, the stop index is not included.

Your stop index is 0, which is the 'h', and so, the output doesn't include the 'h'.

If what you want is to reverse the string, you can:

print(string[::-1])

Output:

olleh

Upvotes: 1

Sercan
Sercan

Reputation: 2169

string[5:0:-1] here, ending index 0 is excluded, which is char h. In order to include fist char as well string[5::-1]

a[start:stop]  # items start through stop-1
a[start:]      # items start through the rest of the array
a[:stop]       # items from the beginning through stop-1
a[:]           # a copy of the whole array

Upvotes: 1

JimmyCarlos
JimmyCarlos

Reputation: 1952

If we look at each term this creates in turn:

string[5] doesn't exist, so adds nothing
string[4] is "o"
string[3] is "l"
string[2] is "l"
string[1] is "e"

string[0] isn't called as Python ranges don't do the last element.

Upvotes: 2

Celius Stingher
Celius Stingher

Reputation: 18377

Remember that the slicing for strings is from:up to (but not including):counter. Therefore, when you pass the -1 as the counter, this would essentially say, from the last character up to the first one, but not including it. Therefore: olle.

See that if you remove the 0, you also get the full string:

string[5::-1]

Returns:

olleh

Upvotes: 1

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