Thanks for flagging this! A couple quick things: - I’m not finding any Prefect docs example about building a “custom Team type.” Did you mean a “custom worker type” or a “custom block”? If you can share the link to the doc page you’re following, I can reproduce exactly. - The code block you pasted just shows “example” — could you re-send the full snippet and the complete error traceback? Please wrap it in triple backticks like:

<your code or error here>

To help me diagnose quickly, please share: - Link to the doc/example you’re using - Your Prefect version (

prefect version

) - Python version and OS - How you’re running it (e.g.,

python script.py

,

prefect deploy

, or

flow.from_source(...).deploy(...)

) Note: If the example you’re using is from Prefect 2.x, some APIs were removed in Prefect 3.x and will fail, for example: -

Deployment.build_from_flow()

was removed; use

flow.from_source(...).deploy(...)

instead -

prefect deployment build

CLI command was removed; use

prefect deploy

instead - GitHub storage blocks were replaced by

.from_source('<https://github.com/owner/repo>')

Once I have the link and the error, I’ll pinpoint the fix or provide the corrected code.

✅ thought for 203.6 seconds

Thanks for the snippet — I can reproduce the error. Root cause:

Team

is a dataclass that requires a

members

argument. Your subclass doesn’t provide it, so the auto-generated

__init__

still expects

members

. Two easy fixes: 1) Quick fix: pass

members

when you construct the team

leader = Agent(name="Project Manager", instructions="Coordinate the team and make final decisions")
specialists = [
    Agent(name="Designer", instructions="Create visual designs"),
    Agent(name="Developer", instructions="Implement technical solutions"),
]

team = HierarchicalTeam(
    members=[leader] + specialists,   # <-- add this
    leader=leader,
    specialists=specialists,
)
result = team.run("Create a landing page for our product")

2) Compute

members

in your subclass (no need to pass it) - Override the

members

field to exclude it from

__init__

, then set it in

__post_init__

. - Call

super().__post_init__()

so

Team

can finish its own setup.

from marvin import Agent, Team
from dataclasses import dataclass, field

@dataclass(kw_only=True)
class HierarchicalTeam(Team):
    """A team with a leader who delegates to specialists."""
    leader: Agent = field(repr=False)
    specialists: list[Agent] = field(repr=False)
    # Override base field so it's not required in __init__
    members: list[Agent] = field(init=False, repr=False, default_factory=list)

    def __post_init__(self):
        self.members = [self.leader] + self.specialists
        self.delegates = {self.leader: self.specialists}
        # Let Team finalize any internal setup
        super().__post_init__()

# Usage
leader = Agent(name="Project Manager", instructions="Coordinate the team and make final decisions")
specialists = [
    Agent(name="Designer", instructions="Create visual designs"),
    Agent(name="Developer", instructions="Implement technical solutions"),
]

team = HierarchicalTeam(leader=leader, specialists=specialists)
result = team.run("Create a landing page for our product")

If this example came directly from the docs, it looks like the missing

members

requirement is a docs bug. I’m happy to file a docs fix once you confirm the page you used. References: - Teams concept - Team API

You’re hitting that error because

Team

is a dataclass that requires the

members

field at init time. Here’s your example fixed by overriding

members

so it’s computed in

__post_init__

and not required in `__init__`:

from marvin import Agent, Team
from dataclasses import dataclass, field

@dataclass(kw_only=True)
class HierarchicalTeam(Team):
    """A team with a leader who delegates to specialists."""
    leader: Agent = field(repr=False)
    specialists: list[Agent] = field(repr=False)

    # Make 'members' not required in __init__; we'll compute it in __post_init__
    members: list[Agent] = field(init=False, repr=False, default_factory=list)

    def __post_init__(self):
        # Build members from the leader and specialists
        self.members = [self.leader] + self.specialists
        # Optionally set up delegation structure
        self.delegates = {self.leader: self.specialists}
        # Let Team perform its normal initialization
        super().__post_init__()

# Usage
leader = Agent(name="Project Manager", instructions="Coordinate the team and make final decisions")
specialists = [
    Agent(name="Designer", instructions="Create visual designs"),
    Agent(name="Developer", instructions="Implement technical solutions"),
]

team = HierarchicalTeam(leader=leader, specialists=specialists)
result = team.run("Create a landing page for our product")
print(result)

If this came from the docs, it’s missing that

members

override. For reference: - Teams concept - Team API

Thanks for confirming — that example on the Teams page is missing the

members

override, which makes

Team.__init__

require

members

. Here’s the same example fixed so it runs as-is:

from marvin import Agent, Team
from dataclasses import dataclass, field

@dataclass(kw_only=True)
class HierarchicalTeam(Team):
    """A team with a leader who delegates to specialists."""
    leader: Agent = field(repr=False)
    specialists: list[Agent] = field(repr=False)

    # 'Team' requires 'members' at init — mark it init=False and compute it here
    members: list[Agent] = field(init=False, repr=False, default_factory=list)

    def __post_init__(self):
        # Build team composition
        self.members = [self.leader] + self.specialists
        self.active_member = self.leader
        self.delegates = {self.leader: self.specialists}
        # Let Team do its normal post-init
        super().__post_init__()

# Usage
leader = Agent(name="Project Manager", instructions="Coordinate the team and make final decisions")
specialists = [
    Agent(name="Designer", instructions="Create visual designs"),
    Agent(name="Developer", instructions="Implement technical solutions"),
]

team = HierarchicalTeam(leader=leader, specialists=specialists)
result = team.run("Create a landing page for our product")
print(result)

I’ll open a docs fix to update the example on the Teams page so others don’t hit this. For reference: - Teams concept docs - Team API reference If you’d like, I can tag you on the PR/issue — just share your GitHub handle.