Skip to main content
The @step decorator declares a method as a step in your Metaflow flow. Every step in a flow must be decorated with @step.

​
Basic Usage

from metaflow import FlowSpec, step

class MyFlow(FlowSpec):
    @step
    def start(self):
        print("Flow started")
        self.next(self.process)
    
    @step
    def process(self):
        self.result = 42
        self.next(self.end)
    
    @step
    def end(self):
        print(f"Result: {self.result}")

if __name__ == '__main__':
    MyFlow()

​
Description

The @step decorator:
  • Identifies methods that should be executed as steps in the workflow
  • Must be the decorator closest to the method definition (after any other decorators)
  • Is required for every method that participates in the flow graph

​
Step Requirements

Every step must:
  1. Be a method of a FlowSpec subclass
  2. Have the @step decorator
  3. Call self.next() to transition to the next step(s), except for the final step

​
Transitions

Steps transition to other steps using self.next():

​
Linear Transitions

@step
def step_a(self):
    self.next(self.step_b)

​
Branching (foreach)

@step
def split(self):
    self.next(self.process, foreach=['a', 'b', 'c'])

@step
def process(self):
    # Runs once for each item
    self.next(self.join)

@step
def join(self, inputs):
    # Joins results from parallel branches
    self.next(self.end)

​
Conditional Branching

@step
def branch(self):
    if self.condition:
        self.next(self.path_a)
    else:
        self.next(self.path_b)

​
Combining with Other Decorators

The @step decorator must be the last decorator applied: 
@batch(cpu=4, memory=8192)
@retry(times=3)
@timeout(hours=1)
@step  # Must be last
def my_step(self):
    pass

​
Special Steps

​
Start Step

Every flow must have a step named start: 
@step
def start(self):
    self.next(self.next_step)

​
End Step

Every flow must have a step named end that doesn’t call self.next(): 
@step
def end(self):
    print("Flow complete")

​
See Also

Build docs developers (and LLMs) love

Get started for freeTalk to us