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. 
s1 = s[8:1:-2]
print(s1)
Output: lool 
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 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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About the author
Java and Python Developer for 20+ years, Open Source Enthusiast, Founder of https://www.askpython.com/, https://www.linuxfordevices.com/, and JournalDev.com (acquired by DigitalOcean). Passionate about writing technical articles and sharing knowledge with others. Love Java, Python, Unix and related technologies. Follow my X @PankajWebDev
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