Multiple ways to get Substring of a string in Python|Slicing example

Multiple ways to get Substring of a string in Python|Slicing example

This tutorial explains how to find substrings or slices of a given string.

For example, if the string contains “hello,” possible substrings include individual characters like ‘h’, ‘e’, ‘l’, ‘l’, ‘o’, or the entire word ‘hello.’

Substring or slicing involves extracting a part of the main string based on given start and end indices.

Let’s understand how strings are stored with index

                    +---+---+---+---+---+---+
                    | h | e | l | l | o | w |
                    +---+---+---+---+---+---+
Start (Positive):     0   1   2   3   4   5
End (positive) :      5   4   3   2   1   0

String slice in Python example

  • Using string[start:end] Syntax

Substrings are calculated using the string[start:end] syntax.

string[start:end]

start and end are the starting and ending indices, returning characters between these indices. The result is a string with characters from start to end-1.

If values are positive, the indices are iterable in the forward direction. For example, in the string hello, start=0 corresponds to h, and end=4 (length-1) corresponds to o.

If values are negative, the indices are iterable in the reverse direction. For example, in the string hello, start=-1 corresponds to o, and end=-4 (-length-1) corresponds to h.

Here is an example

str="hello welcome"

print(str[1:]) # ello welcome
print(str[:1]) # h
print(str[-1:]) # e
print(str[:-1]) # hello welcom
print(str[1:-1]) # ello welcom
print(str[:]) # hello welcome

str[1:]: Start index is 1, and the end index is unknown (until the end of the string). str[:1]: Start is unknown (beginning of the string), and the end is 1. str[-1:]: Start index is the second character from the end of the string, and the end is the beginning in reverse direction. str[:-1]: Start is unknown, and the end is -1 (second character from the end of the string). str[1:-1]: Start is 2 characters from the beginning, and the end is -1 (second character from the end). str[:]: Returns the complete string.

  • Using string[start:end:step]

Another syntax involves using a step value.

string[start:end:step]
  • start: Start index of a string, includes the character in the substring. Default is 0.
  • end: End index of a string, does not include the character in the substring. Default is length - 1.
  • step: Amount of index increase. Default is 1. For negative values, the substring is iterable in the reverse direction.

Here is an example

str="hello welcome"

print(str[1::])# ello welcome
print(str[::1])# hello welcome
print(str[1:2:4]) # e
print(str[-1:None:None]) #e
print(str[1:None:-1]) #eh
print(str[:-1:None]) # hello welcom

This tutorial covers various approaches for finding substrings in Python strings using different approaches.