IndexError: string index out of range

The error message:

IndexError: string index out of range

occurs when you try to access an index in a string that does not exist. Since strings are immutable sequences of characters, their indices must be within the valid range.

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1. Causes and Solutions

Cause 1: Accessing an Index That Does Not Exist

If you try to access an index greater than or equal to the string’s length, Python raises an IndexError.

Incorrect Code:

text = "hello"
print(text[5])  # Error: Index 5 is out of range (valid indices: 0, 1, 2, 3, 4)

Solution: Ensure the index is within the string’s length.

if len(text) > 5:
    print(text[5])
else:
    print("Index is out of range")

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Cause 2: Using a Loop with an Incorrect Range

If you loop beyond the valid indices, you may get this error.

Incorrect Code:

text = "Python"
for i in range(7):  # Error: range(7) includes index 6, which does not exist
    print(text[i])

Solution: Use len(text) to avoid out-of-range errors.

for i in range(len(text)):  # Safe iteration
    print(text[i])

Or use a direct iteration approach.

for char in text:
    print(char)

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Cause 3: Negative Index Beyond String Range

Negative indices refer to elements from the end, but if they exceed the string size, an error occurs.

Incorrect Code:

text = "hello"
print(text[-6])  # Error: Only -1, -2, -3, -4, and -5 are valid

Solution: Ensure the negative index is within range.

if -6 >= -len(text):
    print(text[-6])
else:
    print("Negative index out of range")

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Cause 4: Indexing from an Empty String

If a function returns an empty string and you try to access an index, this error occurs.

Incorrect Code:

empty_string = ""
print(empty_string[0])  # Error: No characters in the string

Solution: Check if the string is empty before accessing an index.

if empty_string:
    print(empty_string[0])
else:
    print("String is empty")

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Cause 5: Slicing with an Out-of-Range Index

If you try to slice a string using an invalid start or stop index, it does not raise an error but returns an empty string.

Example:

text = "hello"
print(text[10:15])  # No error, but returns ''

Solution: Use min() to avoid invalid slicing.

start, end = 2, 10
print(text[start:min(end, len(text))])  # Outputs 'llo'