如何在另一个对象中实例化一个对象，然后从第二个对象调用方法(python)

Question

我有以下代码:

类提交:

id = 0
commits = []
def __init__(self, message=None, changes=None):
    Commit.id += 1
    self.id = Commit.id
    self.message = tuple([message])
    self.changes = tuple(changes)
    Commit.commits.append(self.message + self.changes)
    self.commits = Commit.commits
    self.next = None

类分支:

def __init__(self):
    self.tail = None
    self.head = None
def new_commit(self, commit):
    if not self.head:
        self.head = commit
        self.tail = self.head
    else:
        self.tail.next = commit
        self.tail = self.tail.next

类库:

branches = {}
def __init__(self, name):
    self.name = name
    self.branches = Repository.branches
def branch(self, branch_name):
    self.branch_name = Branch()
    self.branches[branch_name] = self.branch_name
    return self.branches[branch_name]

但是当我这样做来实例化它时:

    repo = Repository("syllabus 2.0")
    repo.branch("master").new_commit(Commit(message="add readme", changes=[("CREATE", "README.md")]))
    print(repo.branch("master").head)

打印None为什么会发生这种情况?

Answer 1

不用管

def branch(self, branch_name):
    if branch_name not in self.branches:
        self.branches[branch_name] = Branch()
        return self.branches[branch_name]
    else:
        return self.branches[branch_name]