Borislav Hadzhiev
Fri Apr 22 2022·3 min read
Photo by Marvin Meyer
The Python "IndexError: string index out of range" occurs when we try to
access an index that doesn't exist in a string. Indexes are zero-based in
Python, so the index of the first character in the string is 0
, and the index
of the last is -1
or len(my_str) - 1
.
Here is an example of how the error occurs.
my_str = 'hello' # ⛔️ IndexError: string index out of range result = my_str[100]
The string hello
has a length of 5
. Since indexes in Python are zero-based,
the first index in the string is 0
, and the last is 4
.
h | e | l | l | o |
---|---|---|---|---|
0 | 1 | 2 | 3 | 4 |
0-4
, we would get an IndexError
.If you need to get the last character in a string, use -1
.
my_str = 'hello' result = my_str[-1] print(result) # 👉️ o print(my_str[-2]) # 👉️ l
When the index starts with a minus, we start counting backwards from the end of the string.
If you need to get the length of the string, use the len()
function.
my_str = 'hello' print(len(my_str)) # 👉️ 5 idx = 5 # ✅ checking if index exists before accessing it if len(my_str) > idx: print(my_str[idx]) else: # 👇️ this runs print(f'index {idx} is out of range')
The len() function returns the length (the number of items) of an object.
The argument the function takes may be a sequence (a string, tuple, list, range or bytes) or a collection (a dictionary, set, or frozen set).
5
, then its last index is 4
(because indexes are zero-based).This means that you can check if the string's length is greater than the index you are trying to access.
An alternative approach is to use a try/except
block and handle the error.
my_str = 'hello' try: result = my_str[100] print(result) except IndexError: print('index out of range') # handle error here
We tried accessing the character at index 100
of the string which raised an
IndexError
exception.
You can handle the error or use the pass
keyword in the except
block.
Note that if you try to access an empty string at a specific index, you'd always
get an IndexError
.
my_str = '' print(my_str) # 👉️ "" print(len(my_str)) # 👉️ 0 # ⛔️ IndexError: string index out of range print(my_str[0])
You should print the string you are trying to access and its length to make sure the variable stores what you expect.
Note that if you use string slicing, you don't get an error if the starting index is out of range.
my_str = 'hello' print(my_str[100:]) # 👉️ "" print(my_str[2:]) # 👉️ "llo"
The first example returns an empty string and doesn't cause an error.
The syntax for string slicing is my_str[start:stop:step]
.
stop
index, you'd get a substring that contains the characters until the end of the original string.If you only need a single character, specify a stop
index.
my_str = 'hello' print(my_str[100:101]) # 👉️ "" print(my_str[2:3]) # 👉️ "l"
Notice that the start
index is inclusive, whereas the stop
index is
exclusive.
In the second example, we start at index 2
, get the character at index 2
and
stop.
This approach is useful if you would rather get an empty string than have to
handle an IndexError
if the index you are trying to access is out of range.