Extracting values

Once you have a Result object, you need to safely extract the contained value or handle the potential error. This page covers the standard ways to unwrap your data.

Pattern matching

The most explicit and Pythonic way to extract values is using the match statement (Python 3.10+). It forces you to handle both success and failure cases structurally.

from result import Result, Ok, Err

def handle_response(result: Result[str, ValueError]) -> str:
    match result:
        case Ok(value):
            return f"Success: {value}"
        case Err(error):
            return f"Error occurred: {error}"

Methods

unwrap

Returns the contained Ok value if the result is a success. If the result is an Err, it raises an exception. Use this only when you are absolutely certain the operation succeeded.

result: Result[int, str] = Ok(42)value = result.unwrap()  # Returns 42
failed_result: Result[int, str] = Err("Something went wrong")
failed_result.unwrap()  # Raises UnwrapError

expect

Similar to unwrap, but allows you to provide a custom error message. The custom message will be included in the raised exception if the result is an Err.

result: Result[dict, str] = Err("Connection timeout")
# Raises UnwrapError: "Database configuration failed: Connection timeout"
config = result.expect("Database configuration failed")

unwrap_or

Returns the contained Ok value if it exists. If the result is an Err, it returns a default value that you provide instead of raising an exception.

success: Result[int, str] = Ok(10)
print(success.unwrap_or(0))  # Outputs: 10
failure: Result[int, str] = Err("File not found")
print(failure.unwrap_or(0))  # Outputs: 0

unwrap_err

The exact opposite of unwrap. Returns the contained Err value if the result failed. If the result is an Ok, it raises an exception.

failure: Result[int, str] = Err("Access denied")
error_msg = failure.unwrap_err()  # Returns "Access denied"
success: Result[int, str] = Ok(200)
success.unwrap_err()  # Raises UnwrapError

resolve

Acts as a lazy version of unwrap_or. Returns the contained Ok value if the result is a success. If it is an Err, it calls the provided fallback function (passing the error into it) and returns its result.This is useful when computing a default value is expensive and should only happen on failure.

def get_backup_value(error: str) -> int:
    # This expensive fallback runs only if needed
    return 999

success: Result[int, str] = Ok(5)
# Returns 5 (get_backup_value is never called)
print(success.resolve(get_backup_value))  

failure: Result[int, str] = Err("Main system failure")
# Calls get_backup_value("Main system failure") and returns 999
print(failure.resolve(get_backup_value))