Tutorial — Level 2: Adding a Transformation

Now we insert a step that converts each character to lowercase. This introduces EACH mode — the step is called once per item.

Sync

```python from typing import NamedTuple from synaflow import pipeline, step, run, PipelineRegistry

class Params(NamedTuple): message: str

def hello(message: str) -> list[str]: return list(message)

def lowercase(hello: str) -> str: return hello.lower()

def printer(lowercase: list[str]) -> None: print(lowercase)

p = pipeline( name="tutorial", params=Params, steps=[ step("hello", fn=hello), step("lowercase", fn=lowercase), step("printer", fn=printer), ], ) catalog = PipelineRegistry() catalog.add(p)

run(catalog.get_dag("tutorial"), Params(message="SynaFlow"))

Output: ['s', 'y', 'n', 'a', 'f', 'l', 'o', 'w']

```

Async

```python from typing import NamedTuple from synaflow import pipeline, step, async_run, PipelineRegistry

class Params(NamedTuple): message: str

async def hello(message: str) -> list[str]: return list(message)

async def lowercase(hello: str) -> str: return hello.lower()

async def printer(lowercase: list[str]) -> None: print(lowercase)

p = pipeline( name="tutorial", params=Params, steps=[ step("hello", fn=hello), step("lowercase", fn=lowercase), step("printer", fn=printer), ], ) catalog = PipelineRegistry() catalog.add(p)

async_run(catalog.get_dag("tutorial"), Params(message="SynaFlow"))

Output: ['s', 'y', 'n', 'a', 'f', 'l', 'o', 'w']

```

What happened?

1. hello outputs list[str] — a collection of 8 characters.
2. lowercase asks for str — a scalar. Because hello outputs an iterable and lowercase expects a scalar, SynaFlow selects EACH mode and calls lowercase once per character.
3. EACH-mode outputs are automatically collected into a list. printer receives list[str] in ALL mode and prints it.

flowchart TD
    hello["hello<br/><i>list[str]</i>"]
    lowercase["lowercase<br/><i>ListType(str)</i>"]
    printer["printer<br/><i>None</i>"]
    message --> hello
    hello --> lowercase
    lowercase --> printer

EACH mode wraps the output type in ListType. lowercase returns str per item, so its output type is ListType(str) — meaning "a list of strings".

You can force the mode explicitly:

step("lowercase", fn=lowercase, mode=StepMode.EACH)

Next

Count the characters in Level 3.