Python TypeError: string indices must be integers

In Python, items of iterable objects such as lists, tuples, or strings can be accessed by using their index numbers.

The index number starts from 0 and increases by 1 for each subsequent item in the object.

For example, here’s how to access the first character in a string:

# Declare a string variable
my_str = "Good Morning!"

# Print the first character in the string
print(my_str[0])  # G

The code above will print G because it’s the first character of the string my_str.

The error TypeError: string indices must be integers occurs when you try to access a character in a string using a string.

For example, suppose you try to access the first character as follows:

my_str = "Good Morning!"

print(my_str['G'])  # ❌

Output:

Traceback (most recent call last):
  File ...
    print(my_str['a'])
TypeError: string indices must be integers

To fix this error, make sure you’re passing an integer inside the square brackets.

The following three scenarios may cause this error:

1. Slicing a string with a wrong syntax
2. Accessing a dictionary in a wrong way
3. Accessing a JSON string like a JSON object

The following examples show how to fix this error in each scenario

1. Slicing a string with a wrong syntax

Aside from passing the index number of a character, you can also extract several characters from a string by using the slicing syntax.

The slicing syntax is as follows:

string_object[start_index:end_index]

The start_index is the starting position of the slice and end_index is the ending position of the slice. The two are separated using a colon (:) operator.

When start_index is not specified, it is assumed to be 0. If end_index is not specified, it is assumed to be the length of the string itself.

The start_index is included in the output, but the end_index is excluded.

Here are some examples of slicing a string in Python:

my_str = "Good Morning!"

# return 'Morning'
print(my_str[5:12])

# return 'Good'
print(my_str[:4])

# return 'ood'
print(my_str[1:4])

# return 'ning!'
print(my_str[8:])

But when you pass a wrong slice syntax, then Python will give you a TypeError:

my_str = "Good Morning!"

# ❌ Use a comma to separate the integers
print(my_str[5,12])

# ❌ Use a dot to separate the integers
print(my_str[5.12])

# ❌ Use a colon but enclosed in quotes
print(my_str['5:12'])

To avoid the error, make sure that the slice syntax has the correct format.

2. Accessing a dictionary in a wrong way

Suppose you have a dictionary object as shown below:

data = {
    "name": "Nathan",
    "age" : 29
}

Now let’s say you want to access the values and print them out using a for loop:

for item in data:
    print(item['name'])  # ❌

The code above will cause a TypeError because the for loop will return the dictionary key in each iteration.

Here’s the right way for accessing a dictionary with a for loop:

data = {
    "name": "Nathan",
    "age" : 29,
    "location": "Japan"
}

for item in data:
    print(item, data[item])

Output:

name Nathan
age 29
location Japan

Because the for loop returns the keys, you can use it to access the dictionary values with the square brackets notation.

3. Accessing a JSON string like a JSON object

In Python, a JSON object is similar to a dictionary object, so you can access its values using the keys.

But at times, you might mistake a string for a JSON object:

json_str = '{"name": "Nathan","age" : 29}'

print(json_str['name'])  # ❌

The json_str object is an encoded JSON string, so trying to access the name value as shown above will cause a TypeError.

To fix this, you need to import the json library and use the json.loads() method:

import json

json_str = '{"name": "Nathan","age" : 29}'

json_obj = json.loads(json_str)

print(json_obj['name'])  # Nathan
print(json_obj['age'])  # 29

The loads() method converts a JSON string into a JSON object, which enables you to access the values like a dictionary.

Keep in mind that you don’t need to call the json.dumps() method.

The dumps() method is used to convert an object to a JSON string. But you already have a string here, so there’s no need to call it 🤷🏻

Conclusion

And there you go! Now you know three common scenarios where you may cause the TypeError: string indices must be integers in Python.

This error happens whenever you try to access a string using a string and not index numbers. It can also occur when you’re working with dictionaries and JSON objects.

The steps in this article should help you resolve the error. Happy coding! ☕️