Python slice string

Filed Under: Python

Python string supports slicing to create substring. Note that Python string is immutable, slicing creates a new substring from the source string and original string remains unchanged.

Python slice string

Python slice string syntax is:


str_object[start_pos:end_pos:step]

The slicing starts with the start_pos index (included) and ends at end_pos index (excluded). The step parameter is used to specify the steps to take from start to end index.

Python String slicing always follows this rule: s[:i] + s[i:] == s for any index ‘i’.

All these parameters are optional – start_pos default value is 0, the end_pos default value is the length of string and step default value is 1.

Let’s look at some simple examples of string slice function to create substring.


s = 'HelloWorld'

print(s[:])

print(s[::])

Output:


HelloWorld
HelloWorld

Note that since none of the slicing parameters were provided, the substring is equal to the original string.

Let’s look at some more examples of slicing a string.


s = 'HelloWorld'
first_five_chars = s[:5]
print(first_five_chars)

third_to_fifth_chars = s[2:5]
print(third_to_fifth_chars)

Output:


Hello
llo

Note that index value starts from 0, so start_pos 2 refers to the third character in the string.

Reverse a String using Slicing

We can reverse a string using slicing by providing the step value as -1.


s = 'HelloWorld'
reverse_str = s[::-1]
print(reverse_str)

Output: dlroWolleH

Let’s look at some other examples of using steps and negative index values.


s1 = s[2:8:2]
print(s1)

Output: loo

Here the substring contains characters from indexes 2,4 and 6.


s1 = s[8:1:-1]
print(s1)

Output: lroWoll

Here the index values are taken from end to start. The substring is made from indexes 1 to 7 from end to start.

python slice string


s1 = s[8:1:-2]
print(s1)

Output: lool

python slice string reverse

Python slice works with negative indexes too, in that case, the start_pos is excluded and end_pos is included in the substring.


s1 = s[-4:-2]
print(s1)

Output: or

python string slicing substring negative index

Python string slicing handles out of range indexes gracefully.


>>>s = 'Python'
>>>s[100:]
''
>>>s[2:50]
'thon'

That’s all for python string slice function to create substring.

You can checkout complete python script and more Python examples from our GitHub Repository.

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