Truncating a String in Python
Someone Gave Me a Syntax to Truncate a String as Follows: String = "My Text String" Print String [0:3] # This Is Just an Example I'm Not Sure What This Is...
Someone gave me a syntax to truncate a string as follows:
string = "My Text String"
print string [0:3] # This is just an example
I'm not sure what this is called (the string[0:3] syntax), so I've had a hard time trying to look it up on the internet and understand how it works. So far I think it works like this:
- string[0:3] # returns the first 3 characters in the string
- string[0:-3] # will return the last 3 characters of the string
- string[3:-3] # seems to truncate the first 3 characters and the last 3 characters
- string[1:0] # I returns 2 single quotes....not sure what this is doing
- string[-1:1] # same as the last one
Anyways, there's probably a few other examples that I can add, but my point is that I'm new to this functionality and I'm wondering what it's called and where I can find more information on this. I'm sure I'm just missing a good reference somewhere.
Thanks for any suggestions, Mike
3 Answers
It's called a slice. From the python documentation under Common Sequence Operations:
s[i:j]
The slice of s from i to j is defined as the sequence of items with index k such that i <= k < j. If i or j is greater than len(s), use len(s). If i is omitted or None, use 0. If j is omitted or None, use len(s). If i is greater than or equal to j, the slice is empty.
As @Uku and @thebjorn said its called Slicing
But one easier way to think is to consider a String like a list, for example you can do:
text = 'Any String'
for letter in text:
print letter
And the same if you want to get a specific letter inside the string:
>> text = 'Any String'
>> text[4]
'S'
ps.: Remember that it's zero based, so text[4] return the 5th letter.
Using Slice it'll return a "substring" text[i:j] from your original String where "i" are the initial index (inclusive) and "j" are the end index (exclusive), for example:
>> text = 'Any String'
>> text[4:6] # from index 4 to 6 exclusive, so it returns letters from index 4 and 5
'St'
>> text[0:4]
'Any '
>> text[:4] # omiting the "i" index means i = 0
'Any '
>> text[4:] # omitting the "j" index means until the end of the string
A negative index is relative to the end of the String like making a substitution from the negative index to "len(text) + i".
In our case len(text) is 10, a negative index -1 will be like using text[9] to get the last element, -2 will return the last but one element and so forth.
In examples you sent, string[0:-3] should return everything but last 3 characters and string[3:-3] should return everything but first 3 and last 3.
Hope it helpped.
It's called slicing, read more about it e.g. here:
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