<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def is_valid_field_name(value):
 """Ensure field name is valid."""

    leftovers = re.sub(r"\w", "", value)
    leftovers = re.sub(r"-", "", leftovers)
    if leftovers != "" or value[0].isdigit() or value[0] in ["-", "_"] or " " in value:
        return False
    return True