How to search a string in backwards direction in Python?

In this article, we are going to find out how to search a string in backward direction in Python.

Python provides two main methods for searching strings from right to left: rindex() and rfind(). Both methods find the rightmost occurrence of a substring but handle missing substrings differently.

Using rindex() Method

The rindex() method returns the highest index of any substring in the given string. By highest index, we mean that if a substring appears multiple times, rindex() returns the index of the rightmost occurrence.

The main disadvantage is that it throws a ValueError if the substring is not found.

Syntax

string.rindex(substring, start, end)

Example 1 ? Finding Existing Substring

In the example given below, we are finding the last index of a specific substring using the rindex() method ?

text = "Welcome to Tutorialspoint"
substring = "Tutorial"

print("The given string is:")
print(text)

print("Finding the last index of", substring)
print(text.rindex(substring))

The output of the above example is ?

The given string is:
Welcome to Tutorialspoint
Finding the last index of Tutorial
11

Example 2 ? Substring Not Found

When the substring is not found, rindex() raises a ValueError ?

text = "Welcome to Tutorialspoint"
substring = "Hello"

print("The given string is:")
print(text)

try:
    print("Finding the last index of", substring)
    print(text.rindex(substring))
except ValueError as e:
    print("Error:", e)

The output of the above example is ?

The given string is:
Welcome to Tutorialspoint
Finding the last index of Hello
Error: substring not found

Using rfind() Method

The rfind() method overcomes the drawback of rindex(). It has similar functionality but returns -1 instead of throwing an exception when the substring is not found.

Example 1 ? Finding Existing Substring

The rfind() method works identically to rindex() when the substring exists ?

text = "Welcome to Tutorialspoint"
substring = "Tutorial"

print("The given string is:")
print(text)

print("Finding the last index of", substring)
print(text.rfind(substring))

The output of the above example is ?

The given string is:
Welcome to Tutorialspoint
Finding the last index of Tutorial
11

Example 2 ? Substring Not Found

When the substring is not found, rfind() returns -1 without raising an exception ?

text = "Welcome to Tutorialspoint"
substring = "Hello"

print("The given string is:")
print(text)

result = text.rfind(substring)
print("Finding the last index of", substring)
print(result)

if result == -1:
    print("Substring not found")
else:
    print("Substring found at index:", result)

The output of the above example is ?

The given string is:
Welcome to Tutorialspoint
Finding the last index of Hello
-1
Substring not found

Practical Example ? Multiple Occurrences

Here's an example showing how both methods handle multiple occurrences ?

text = "Python is great, Python is powerful"
substring = "Python"

print("String:", text)
print("Using rfind():", text.rfind(substring))
print("Using rindex():", text.rindex(substring))

# Show all occurrences for comparison
print("All occurrences:")
start = 0
while True:
    pos = text.find(substring, start)
    if pos == -1:
        break
    print(f"Found at index: {pos}")
    start = pos + 1

The output shows that both methods return the rightmost occurrence ?

String: Python is great, Python is powerful
Using rfind(): 17
Using rindex(): 17
All occurrences:
Found at index: 0
Found at index: 17

Comparison

Conclusion

Use rfind() for safe backward string searching that won't raise exceptions. Use rindex() only when you're certain the substring exists and want explicit error handling for missing substrings.