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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def pretty_print_error(err_json):
 """Pretty print Flask-Potion error messages for the user."""

    # Special case validation errors
    if len(err_json) == 1 and "validationOf" in err_json[0]:
        required_fields = ", ".join(err_json[0]["validationOf"]["required"])
        return "Validation error. Requires properties: {}.".format(required_fields)

    # General error handling
    msg = "; ".join(err.get("message", "") for err in err_json)

    # Fallback
    if not msg:
        msg = "Bad request."
    return msg