Add Output.concat to Python (#3006)

Fixes #2366

CHANGELOG.md

@@ -3,9 +3,11 @@ CHANGELOG
 
 ## Unreleased
 
+- Add `Ouput.concat` to Python SDK [#3006](https://github.com/pulumi/pulumi/pull/3006)
+
 ### Compatibility
 
-* Deprecated functions in `@pulumi/pulumi` will now issue warnings if you call them.  Please migrate
+- Deprecated functions in `@pulumi/pulumi` will now issue warnings if you call them.  Please migrate
   off of these functions as they will be removed in a future release.  The deprecated functions are.
   1. `function computeCodePaths(extraIncludePaths?: string[], ...)`.  Use the `computeCodePaths`
      overload that takes a `CodePathOptions` instead.

sdk/python/lib/pulumi/output.py

@@ -317,3 +317,21 @@ class Output(Generic[T]):
         known_futures = asyncio.ensure_future(is_known(all_outputs))
         secret_futures = asyncio.ensure_future(is_secret(all_outputs))
         return Output(resources, value_futures, known_futures, secret_futures)
+
+    @staticmethod
+    def concat(*args: List[Input[str]]) -> 'Output[str]':
+        """
+        Concatenates a collection of Input[str] into a single Output[str].
+
+        This function takes a sequence of Input[str], stringifies each, and concatenates all values
+        into one final string. This can be used like so:
+
+            url = Output.concat("http://", server.hostname, ":", loadBalancer.port)
+
+        :param List[Input[str]] args: A list of string Inputs to concatenate.
+        :return: A concatenated output string.
+        :rtype: Output[str]
+        """
+
+        transformed_items = [Output.from_input(v) for v in args]
+        return Output.all(*transformed_items).apply("".join)

sdk/python/lib/test/langhost/output_all/__main__.py

@@ -11,7 +11,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-from pulumi import Output, CustomResource
+from pulumi import Output, CustomResource, export
 
 class MyResource(CustomResource):
     number: Output[str]
@@ -43,3 +43,7 @@ res2.number.apply(lambda n: assert_eq(n, 3))
 # Output.all combines a list of outputs into an output of a list.
 resSum = Output.all(res1.number, res2.number).apply(lambda l: l[0] + l[1])
 FinalResource("testResource3", resSum)
+
+# Test additional Output helpers
+hello_world = Output.concat("Hello ", Output.from_input("world!")).apply(lambda s: assert_eq(s, "Hello world!"))
+export("helloworld", hello_world)