‘key of type tuple not found and not a multiindex’

When you receive the error message “Key of type tuple not found and not a multiindex” in your code, it means that you are trying to access a value from a dictionary using a tuple as the key, but that particular key does not exist in the dictionary. This error can also occur when you are working with a multi-index object.

To better understand this error, let’s consider an example:

# Creating a dictionary
data = {
    ('John', 25): 85,
    ('Alice', 28): 92,
    ('Bob', 26): 78
}

# Accessing the value using a tuple key
print(data[('John', 25)])  # Output: 85

# Accessing a non-existent key
print(data[('Alice', 26)])  # Error: KeyError: ('Alice', 26)
    

In the example above, we have a dictionary called ‘data’ where the keys are tuples representing a person’s name and age, and the values are their respective scores. When we try to access the value using a valid tuple key, it works fine. However, if we try to access the value using a tuple key that does not exist in the dictionary, we encounter a KeyError.

If you are working with a multi-index object, this error can also occur when you provide an index tuple that does not exist.

# Importing pandas library
import pandas as pd

# Creating a multi-index DataFrame
data = pd.DataFrame({'Score': [85, 92, 78]}, index=[['John', 'Alice', 'Bob'], [25, 28, 26]], columns=['Score'])

# Accessing the value using a valid index tuple
print(data.loc[('John', 25), 'Score'])  # Output: 85

# Accessing a non-existent index tuple
print(data.loc[('Alice', 26), 'Score'])  # Error: KeyError: ('Alice', 26)
    

Here, we create a multi-index DataFrame using pandas. The index consists of tuples representing a person's name and age, and the only column is the score. When we try to access a score using a valid index tuple, it works fine. However, if we provide an index tuple that does not exist in the DataFrame, we encounter a KeyError.

To resolve this error, you need to ensure that the key or index tuple you are using to access a value actually exists in the dictionary or DataFrame. You can either check for the existence of the key before accessing it using the 'in' operator for dictionaries, or by using the 'contains' method for pandas DataFrames. Alternatively, you can modify your code to handle this error gracefully by providing default values or appropriate error handling mechanisms.

Here is an example of how you can handle this error:

# Creating a dictionary
data = {
    ('John', 25): 85,
    ('Alice', 28): 92,
    ('Bob', 26): 78
}

# Handling the KeyError
key = ('Alice', 26)
if key in data:
    print(data[key])
else:
    print("Key does not exist")

# Output: Key does not exist
    

In the code above, we check if the key exists in the dictionary before accessing it. If the key exists, we print the corresponding value. Otherwise, we handle the error by printing a custom message.