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.
Note that, String slicing creates a new string, it does not modify the original string, as strings in Python are immutable.
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
3- If the start index is greater than or equal to the end index and increment step is positive, an empty string is returned.
s = "Python String Slicing"
print("substring is ", s[12: 8 : 1])
4- If value of the end index is greater than the length of the string then subtring will include characters upto string length, rather than raising an error.
s = "Python String Slicing"
print("substring is", s[14: 40 : 1])
Output
substring is Slicing
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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