String Slicing in Python

String in Python is stored as an array so array indexing can be used to access characters of a String, for example str[0] returns first character of the String str. You may have a scenario where you want to access a part of String rather than a single character, in that case you can use string slicing using slice operator in Python.

Python string slicing

Format of String slicing is as follows-

Stringname[start_position: end_position: increment_step]

• start_position is the index from which the string slicing starts, start_position is included.
• end_position is the index at which the string slicing ends, end_position is excluded.
• increment_step indicates the step size. For example if step is given as 2 then every alternate character from start_position is accessed.

All of these parameters are optional, if start_position is not specified then the slicing starts from index 0. If end_position is not specified then the slicing ends at string_length – 1 (last index). If increment_step is not specified then increment step is 1 by default.

Python string slicing examples

1- A simple example where substring from index 2..3 is required.

s = "Python String Slicing"
print(s[2: 4: 1])

Output

th

Here slicing is done from index 2 (start_pos) to index 3 (end_pos-1). Step size is 1.

2- If no parameters are specified.

s = "Python String Slicing"
#both are valid
print(s[:])
print(s[: :])

Output

Python String Slicing
Python String Slicing

3- String slicing when step size is greater than one.

s = "Python String Slicing"
print(s[3: 8 : 2])

Output

hnS

Since the step size is 2 so every other character with in the limits of start_pos and end_pos is accessed.

4- Using string slicing in conjunction with other Python string methods. For example if there is a data in dd/mm/yyyy format and you want to access only the month part. In this case you can use index method to specify the start and end positions for slicing.

s = "03/05/2019"
print(s[s.index("/")+1: s.rindex("/") : 1])

Output

05

String slicing with negative indexing

In string in Python you can also use negative indexing. When negative number is used as index String is accessed backward so -1 refers to the last character, -2 second last and so on.

1- Reversing the string using slicing. By providing increment_step as -1 you can reverse a string.

s = "Hello World"
reversed = s[: :-1]
print(reversed)

Output

dlroW olleH

2- Using negative value as start position and step size is +1.

s = "Hello World"
str = s[-5: :]
print(str)

Output

World

Here step size is +1 so the indices that are accessed are -5, -4, -3, -2, -1

That's all for this topic String Slicing in Python. If you have any doubt or any suggestions to make please drop a comment. Thanks!

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