unless-handler 0.1

Lightweight python library for error handling

Unless

Unless is a lightweight python library designed to simplify error handling. It introduces the Result class that encapsulates the result of a function call, which can be either the result value, an error, or both.

Install

pip3 install unless

Usage

💡 Remember

Result class has 2 properties,

• value - The return value of the function
• error - Information about the error if there was any

• Import the Result class and traceback.format_exc for tracebacks

  from unless.result import Result
  
  from traceback import format_exc # Optional
  

• Integrate Result into your function

  • Initialize the Result class (specify the return type for type hints)

    def cool():
        to_return = Result[list]()
                            ^
                        Return type
    

    [list] is the return type of the function and is there so we can have type hints. It is OPTIONAL and Result() works too.

  • Set the return value

    • Use value property of the Result class to set return value

    # <initialized>.value = <value to return>
    to_return.value = [1, 2, 3]
    

  • Catch and set errors

    • Use error property of the Result class to set errors

    try:
        ...
    except:
        # <initialized>.error = <traceback.format_exc()>
        to_return.error = format_exc()
    

  • Return the result

    return to_return
    

• Calling your function

  • See result using the value property

    called = my_function()
    
    called.value
    

  • See error using the error property

    called.error
    

  • Or better yet, use the unless method

    called = my_function().unless()
    
    # called is now called.value and errors are handled using handler function
    # for more info check "Examples"
    

Examples

Basic usage

def cool():
    to_return = Result[list]()
    try:
        to_return.value = [1, 2, 3]
        raise ValueError("Annoying error...")
    except Exception as e:
        to_return.error = traceback.format_exc()
    return to_return

# Calling the function
x = cool().unless()
print(x)

Custom error handling

You can call functions with custom error handling logic using Result.unless method that your function returns.

• You can pass any python function to the unless method
• Your handler function must accept at least 1 argument (traceback str)
• Handler function can have keyword arguments (x.unless(func, arg1="first", arg2="second"))

def custom_handler(e, notes):
    logging.warn(f"{e} \n\nNotes: {notes}")

x = cool().unless(
        custom_handler,
        notes="Probably happend because the function was hot"
    )
print(x)