What is the best practice to do with temporary (unused) list?-CodePudding

I've a code snippet below which gets the dataclass variables (keys) with "_dg" prefix, then gets the attribute of each key according to declaration order and appends them into a list. At the end this will be merged into a single element and returned as a string.

def create_decrypted_EFSOD(self) -> str:

    _ = []
    try:
        for attr in list(self.__dict__.keys()):
            if attr.startswith("_dg"):
                _.append(self.__getattribute__(attr))

        return "".join(_)

    finally:
        del _

Where my dataclass is declared as:

@dataclass
class PassiveAuthenticator:
    """
    Passive Authentication of eMRTD Documents for Inspection Systems (IFD's). Protects against IC forging.

    Refers to "Doc. 9303, Machine Readable Travel Documents, Part 11 - Security Mechanisms for MRTDS" by ICAO, 2021,
    Section 6.1 and Appendix G for more details about security protocols.

    """
    _dg1: str
    _dg2: str
    _dg3: str
    .
    .

I know the _ variable always refers to last returned value, that is why I used it to avoid creating unnecessary variable, but creating a temporary variable still bothers me. What is the best practice for this situation?

Also, does deleting _ variable mean anything since it'll be redeclared again? Since I'm a C dev it's a habit to deallocate.

CodePudding user response：

To repeat what was already said in the comments:

no, _ does not refer to the last returned variable
no, _ is not a good name for the variable, it should be used on variables that are unused but your variable is used
no, python has automatic GC and you do not need to explicitly del _.

Therefore your code should simply be

def create_decrypted_EFSOD(self) -> str:
    matching_attributes = []
    for attr in list(self.__dict__.keys()):
        if attr.startswith("_dg"):
            matching_attributes.append(self.__getattribute__(attr))

    return "".join(matching_attributes)

or simplified using a list comprehension

def create_decrypted_EFSOD(self) -> str:
    return "".join(value for attr, value in self.__dict__.items() if attr.startswith("_dg"))