TypeError：__init __（）缺少1个必需的位置参数：分支，但提供了参数

Question

I have a subclass of another class. Both have the same signature for the __init__ method. My caller supplies all required arguments. Yet I still get the missing argument error.

I have tried different ways of calling the super class's __init__ method.

Base Class init function (imported from another file):

class Gerrit:
    connections = {
        'consumer': MyGerritClient(host='gerrit.consumer.com', username=getpass.getuser()),
        'b2b': MyGerritClient(host='gerrit.b2b.com', username=getpass.getuser())
    }

    def __init__(self, segment, rev_id, branches):
        print("TRACE: Gerrit::__init__()")
        self.branches = branches
        self.review = None  # Type: GerritChange
        self.gerrit_client = self.connections[segment]
        for review_candidate in self.gerrit_client.query(rev_id):
            if self.branch_is_valid(review_candidate.branch) and review_candidate.status != 'ABANDONED':
                self.review = review_candidate
        self.approved = False
        self.rev_id = rev_id
        self.merged = False

Child Class __init__ method:

class CvGerrit(Gerrit):
    def __init__(self, segment, rev_id, branches):
        Gerrit.__init__(segment, rev_id, branches)

Caller:

review = CvGerrit(segment='consumer', rev_id=gerrit_id, branches=my_branches)

I expect that I can construct the child class, CvGerrit . Instead I get the missing positional argument error. Does it matter that the other uses of the base class take a list for the branches argument, while the caller is passing a dict ? This is intentional, and the whole reason for the subclassing, that I may process this collection differently using an overridden function in the child.

Answer 1

You will want to call either

Gerrit.__init__(segment, rev_id, branches)

or

super().__init__(segment, rev_id, branches)

By itself, __init__ is just another function object, so when you access it through the class, you must pass all parameters, including self . When you access it through an instance or super , you get a bound method with self already pre-inserted into the argument list.