Make steps callable, add dag/steps callable examples (#715)

**Pull Request Checklist**
- [x] Fixes #714 
- [x] Tests added
- [x] Documentation/examples added
- [x] [Good commit messages](https://cbea.ms/git-commit/) and/or PR
title

**Description of PR**
Currently, Steps aren't callable as a template under another DAG/Steps
context, while DAGs themselves are. This PR adds the
`CallableTemplateMixin` to Steps and adds examples for both Steps and
dags to show the callable usage.

---------

Signed-off-by: Elliot Gunton <[email protected]>

docs/examples/workflows/callable_dag.md

@@ -0,0 +1,100 @@
+# Callable Dag
+
+
+
+
+
+
+=== "Hera"
+
+    ```python linenums="1"
+    from hera.workflows import DAG, Parameter, Workflow, script
+
+
+    @script()
+    def hello(name: str):
+        print("Hello, {name}!".format(name=name))
+
+
+    with Workflow(
+        generate_name="callable-dag-",
+        entrypoint="calling-dag",
+    ) as w:
+        with DAG(name="my-dag", inputs=Parameter(name="my-dag-input")) as my_dag:
+            hello(name="hello-1", arguments={"name": "hello-1-{{inputs.parameters.my-dag-input}}"})
+            hello(name="hello-2", arguments={"name": "hello-2-{{inputs.parameters.my-dag-input}}"})
+
+        with DAG(name="calling-dag") as d:
+            t1 = my_dag(name="call-1", arguments={"my-dag-input": "call-1"})
+            t2 = my_dag(name="call-2", arguments={"my-dag-input": "call-2"})
+            t1 >> t2
+    ```
+
+=== "YAML"
+
+    ```yaml linenums="1"
+    apiVersion: argoproj.io/v1alpha1
+    kind: Workflow
+    metadata:
+      generateName: callable-dag-
+    spec:
+      entrypoint: calling-dag
+      templates:
+      - dag:
+          tasks:
+          - arguments:
+              parameters:
+              - name: name
+                value: hello-1-{{inputs.parameters.my-dag-input}}
+            name: hello-1
+            template: hello
+          - arguments:
+              parameters:
+              - name: name
+                value: hello-2-{{inputs.parameters.my-dag-input}}
+            name: hello-2
+            template: hello
+        inputs:
+          parameters:
+          - name: my-dag-input
+        name: my-dag
+      - inputs:
+          parameters:
+          - name: name
+        name: hello
+        script:
+          command:
+          - python
+          image: python:3.8
+          source: 'import os
+
+            import sys
+
+            sys.path.append(os.getcwd())
+
+            import json
+
+            try: name = json.loads(r''''''{{inputs.parameters.name}}'''''')
+
+            except: name = r''''''{{inputs.parameters.name}}''''''
+
+
+            print(''Hello, {name}!''.format(name=name))'
+      - dag:
+          tasks:
+          - arguments:
+              parameters:
+              - name: my-dag-input
+                value: call-1
+            name: call-1
+            template: my-dag
+          - arguments:
+              parameters:
+              - name: my-dag-input
+                value: call-2
+            depends: call-1
+            name: call-2
+            template: my-dag
+        name: calling-dag
+    ```
+

docs/examples/workflows/callable_steps.md

@@ -0,0 +1,96 @@
+# Callable Steps
+
+
+
+
+
+
+=== "Hera"
+
+    ```python linenums="1"
+    from hera.workflows import Parameter, Steps, Workflow, script
+
+
+    @script()
+    def hello(name: str):
+        print("Hello, {name}!".format(name=name))
+
+
+    with Workflow(
+        generate_name="callable-steps-",
+        entrypoint="calling-steps",
+    ) as w:
+        with Steps(name="my-steps", inputs=Parameter(name="my-step-input")) as my_steps:
+            hello(name="hello-1", arguments={"name": "hello-1-{{inputs.parameters.my-step-input}}"})
+            hello(name="hello-2", arguments={"name": "hello-2-{{inputs.parameters.my-step-input}}"})
+
+        with Steps(name="calling-steps") as s:
+            my_steps(name="call-1", arguments={"my-step-input": "call-1"})
+            my_steps(name="call-2", arguments={"my-step-input": "call-2"})
+    ```
+
+=== "YAML"
+
+    ```yaml linenums="1"
+    apiVersion: argoproj.io/v1alpha1
+    kind: Workflow
+    metadata:
+      generateName: callable-steps-
+    spec:
+      entrypoint: calling-steps
+      templates:
+      - inputs:
+          parameters:
+          - name: my-step-input
+        name: my-steps
+        steps:
+        - - arguments:
+              parameters:
+              - name: name
+                value: hello-1-{{inputs.parameters.my-step-input}}
+            name: hello-1
+            template: hello
+        - - arguments:
+              parameters:
+              - name: name
+                value: hello-2-{{inputs.parameters.my-step-input}}
+            name: hello-2
+            template: hello
+      - inputs:
+          parameters:
+          - name: name
+        name: hello
+        script:
+          command:
+          - python
+          image: python:3.8
+          source: 'import os
+
+            import sys
+
+            sys.path.append(os.getcwd())
+
+            import json
+
+            try: name = json.loads(r''''''{{inputs.parameters.name}}'''''')
+
+            except: name = r''''''{{inputs.parameters.name}}''''''
+
+
+            print(''Hello, {name}!''.format(name=name))'
+      - name: calling-steps
+        steps:
+        - - arguments:
+              parameters:
+              - name: my-step-input
+                value: call-1
+            name: call-1
+            template: my-steps
+        - - arguments:
+              parameters:
+              - name: my-step-input
+                value: call-2
+            name: call-2
+            template: my-steps
+    ```
+

examples/workflows/callable-dag.yaml

@@ -0,0 +1,63 @@
+apiVersion: argoproj.io/v1alpha1
+kind: Workflow
+metadata:
+  generateName: callable-dag-
+spec:
+  entrypoint: calling-dag
+  templates:
+  - dag:
+      tasks:
+      - arguments:
+          parameters:
+          - name: name
+            value: hello-1-{{inputs.parameters.my-dag-input}}
+        name: hello-1
+        template: hello
+      - arguments:
+          parameters:
+          - name: name
+            value: hello-2-{{inputs.parameters.my-dag-input}}
+        name: hello-2
+        template: hello
+    inputs:
+      parameters:
+      - name: my-dag-input
+    name: my-dag
+  - inputs:
+      parameters:
+      - name: name
+    name: hello
+    script:
+      command:
+      - python
+      image: python:3.8
+      source: 'import os
+
+        import sys
+
+        sys.path.append(os.getcwd())
+
+        import json
+
+        try: name = json.loads(r''''''{{inputs.parameters.name}}'''''')
+
+        except: name = r''''''{{inputs.parameters.name}}''''''
+
+
+        print(''Hello, {name}!''.format(name=name))'
+  - dag:
+      tasks:
+      - arguments:
+          parameters:
+          - name: my-dag-input
+            value: call-1
+        name: call-1
+        template: my-dag
+      - arguments:
+          parameters:
+          - name: my-dag-input
+            value: call-2
+        depends: call-1
+        name: call-2
+        template: my-dag
+    name: calling-dag

examples/workflows/callable-steps.yaml

@@ -0,0 +1,60 @@
+apiVersion: argoproj.io/v1alpha1
+kind: Workflow
+metadata:
+  generateName: callable-steps-
+spec:
+  entrypoint: calling-steps
+  templates:
+  - inputs:
+      parameters:
+      - name: my-step-input
+    name: my-steps
+    steps:
+    - - arguments:
+          parameters:
+          - name: name
+            value: hello-1-{{inputs.parameters.my-step-input}}
+        name: hello-1
+        template: hello
+    - - arguments:
+          parameters:
+          - name: name
+            value: hello-2-{{inputs.parameters.my-step-input}}
+        name: hello-2
+        template: hello
+  - inputs:
+      parameters:
+      - name: name
+    name: hello
+    script:
+      command:
+      - python
+      image: python:3.8
+      source: 'import os
+
+        import sys
+
+        sys.path.append(os.getcwd())
+
+        import json
+
+        try: name = json.loads(r''''''{{inputs.parameters.name}}'''''')
+
+        except: name = r''''''{{inputs.parameters.name}}''''''
+
+
+        print(''Hello, {name}!''.format(name=name))'
+  - name: calling-steps
+    steps:
+    - - arguments:
+          parameters:
+          - name: my-step-input
+            value: call-1
+        name: call-1
+        template: my-steps
+    - - arguments:
+          parameters:
+          - name: my-step-input
+            value: call-2
+        name: call-2
+        template: my-steps

examples/workflows/callable_dag.py

@@ -0,0 +1,20 @@
+from hera.workflows import DAG, Parameter, Workflow, script
+
+
+@script()
+def hello(name: str):
+    print("Hello, {name}!".format(name=name))
+
+
+with Workflow(
+    generate_name="callable-dag-",
+    entrypoint="calling-dag",
+) as w:
+    with DAG(name="my-dag", inputs=Parameter(name="my-dag-input")) as my_dag:
+        hello(name="hello-1", arguments={"name": "hello-1-{{inputs.parameters.my-dag-input}}"})
+        hello(name="hello-2", arguments={"name": "hello-2-{{inputs.parameters.my-dag-input}}"})
+
+    with DAG(name="calling-dag") as d:
+        t1 = my_dag(name="call-1", arguments={"my-dag-input": "call-1"})
+        t2 = my_dag(name="call-2", arguments={"my-dag-input": "call-2"})
+        t1 >> t2

examples/workflows/callable_steps.py

@@ -0,0 +1,19 @@
+from hera.workflows import Parameter, Steps, Workflow, script
+
+
+@script()
+def hello(name: str):
+    print("Hello, {name}!".format(name=name))
+
+
+with Workflow(
+    generate_name="callable-steps-",
+    entrypoint="calling-steps",
+) as w:
+    with Steps(name="my-steps", inputs=Parameter(name="my-step-input")) as my_steps:
+        hello(name="hello-1", arguments={"name": "hello-1-{{inputs.parameters.my-step-input}}"})
+        hello(name="hello-2", arguments={"name": "hello-2-{{inputs.parameters.my-step-input}}"})
+
+    with Steps(name="calling-steps") as s:
+        my_steps(name="call-1", arguments={"my-step-input": "call-1"})
+        my_steps(name="call-2", arguments={"my-step-input": "call-2"})

src/hera/workflows/dag.py

@@ -17,7 +17,12 @@
 from hera.workflows.task import Task
 
 
-class DAG(IOMixin, TemplateMixin, CallableTemplateMixin, ContextMixin):
+class DAG(
+    IOMixin,
+    TemplateMixin,
+    CallableTemplateMixin,
+    ContextMixin,
+):
     """A DAG template invocator is used to define Task dependencies as an acyclic graph.
 
     DAG implements the contextmanager interface so allows usage of `with`, under which any

src/hera/workflows/steps.py

@@ -7,6 +7,7 @@
 
 from hera.workflows._mixins import (
     ArgumentsMixin,
+    CallableTemplateMixin,
     ContextMixin,
     IOMixin,
     ItemMixin,
@@ -103,9 +104,10 @@ def _build_step(self) -> List[_ModelWorkflowStep]:
 
 
 class Steps(
-    ContextMixin,
     IOMixin,
     TemplateMixin,
+    CallableTemplateMixin,
+    ContextMixin,
 ):
     """A Steps template invocator is used to define a sequence of steps which can run sequentially or in parallel.