def jit(signature_or_function=None, locals={}, target='cpu', cache=False, **options):
    if 'argtypes' in options:
        raise DeprecationError(_msg_deprecated_signature_arg.format('argtypes'))
    if 'restype' in options:
        raise DeprecationError(_msg_deprecated_signature_arg.format('restype'))

    # Handle signature
    if signature_or_function is None:
        # No signature, no function
        pyfunc = None
        sigs = None
    elif isinstance(signature_or_function, list):
        # A list of signatures is passed
        pyfunc = None
        sigs = signature_or_function
    elif sigutils.is_signature(signature_or_function):
        # A single signature is passed
        pyfunc = None
        sigs = [signature_or_function]
    else:
        # A function is passed
        pyfunc = signature_or_function
        sigs = None

    wrapper = _jit(sigs, locals=locals, target=target, cache=cache,
                   targetoptions=options)
    if pyfunc is not None:
        return wrapper(pyfunc)
    else:
        return wrapper
This decorator is used to compile a Python function into native code.
dataset/ETHPy150Open numba/numba/numba/decorators.py/jit