python sdk readme guide (#10123)

* python sdk readme guide

* add tag name rule

* address comments

documentation/code-gen/configure-python-sdk.md

@@ -0,0 +1,237 @@
+# Readme Configuration Guide for Python SDK
+This file describe how to configure readme files to make it available for Python SDK code generation.
+
+## Common Configuration
+Configure basic package information.
+
+### Basic Information
+Configure package title/description/tag.
+~~~~
+// file: readme.md
+
+``` yaml
+title: AppconfigurationConfigurationClient
+description: Appconfiguration Configuration Client
+openapi-type: arm
+tag: package-2019-10-01             // refer to below tag description
+```
+~~~~
+
+### tag
+Tags are used to define what swagger files are used in specific client SDK. In Single-API client, only one tag can be used to generate SDK client.
+A tag can contains a bunch of swagger files which are used to generate the SDK. 
+
+The name of a tag should be in form of package-yyyy-mm-dd[-xxx], for example below tag names are available:
+- package-2020-02-03
+- package-2020-03-22-preview
+- package-2020-05-03-only
+
+while those are invalid names:
+- 2020-03-04
+- package-preview-2020-03-04
+
+A tag can be configured like below:
+~~~~
+// file: readme.md
+
+
+### Tag: package-2019-10-01
+
+These settings apply only when `--tag=package-2020-05-01` is specified on the command line.
+
+``` yaml $(tag) == 'package-2019-10-01'
+input-file:
+- Microsoft.AppConfiguration/stable/2019-10-01/appconfiguration.json
+- Microsoft.AppConfiguration/stable/2019-10-01/xxxx.json
+```
+~~~~
+
+
+### all-api-versions
+All swagger files need to be added into the all-api-version section. For Example:
+
+~~~~
+// file: readme.md
+
+
+## Multi-API/Profile support for AutoRest v3 generators 
+
+AutoRest V3 generators require the use of `--tag=all-api-versions` to select api files.
+
+This block is updated by an automatic script. Edits may be lost!
+
+``` yaml $(tag) == 'all-api-versions' /* autogenerated */
+# include the azure profile definitions from the standard location
+require: $(this-folder)/../../../profiles/readme.md
+
+# all the input files across all versions
+input-file:
+  - Microsoft.AppConfiguration/stable/2019-10-01/appconfiguration.json
+  - Microsoft.AppConfiguration/stable/2019-10-01/xxxx.json
+  - Microsoft.AppConfiguration/stable/2018-10-01/appconfiguration.json
+  - ...
+~~~~
+
+
+## Swagger to SDK
+To make python SDK can be generated from the tag, swagger-to-sdk need to be configured:
+
+~~~
+// file: readme.md
+
+## Swagger to SDK
+
+This section describes what SDK should be generated by the automatic system.
+This is not used by Autorest itself.
+
+``` yaml $(swagger-to-sdk)
+swagger-to-sdk:
+  - repo: azure-sdk-for-python
+  - ...
+
+
+## Python
+
+See configuration in [readme.python.md](./readme.python.md)
+~~~
+
+## Python Configuration
+Python dedicated configurations are configured in readme.python.md.
+A typical readme.python.md is like this:
+
+~~~
+// file: readme.python.md
+
+
+## Python
+
+These settings apply only when `--python` is specified on the command line.
+Please also specify `--python-sdks-folder=<path to the root directory of your azure-sdk-for-python clone>`.
+Use `--python-mode=update` if you already have a setup.py and just want to update the code itself.
+
+``` yaml !$(track2)                         // For track1: basic Python package information 
+python-mode: create
+python:
+  azure-arm: true
+  license-header: MICROSOFT_MIT_NO_VERSION
+  payload-flattening-threshold: 2
+  namespace: azure.mgmt.appconfiguration
+  package-name: azure-mgmt-appconfiguration
+  package-version: 0.1.0
+  clear-output-folder: true
+```
+
+These settings apply only when `--track2` is specified on the command line.
+
+``` yaml $(track2)                          // For track2: basic Python package information 
+azure-arm: true
+license-header: MICROSOFT_MIT_NO_VERSION
+package-name: azure-mgmt-appconfiguration
+no-namespace-folders: true
+package-version: 0.1.0
+```
+
+``` yaml $(python-mode) == 'update'
+// --------------- For track1 -----------------
+python:                                     
+  no-namespace-folders: true
+  output-folder: $(python-sdks-folder)/appconfiguration/azure-mgmt-appconfiguration/azure/mgmt/appconfiguration
+
+// --------------- For track2 -----------------
+no-namespace-folders: true
+output-folder: $(python-sdks-folder)/appconfiguration/azure-mgmt-appconfiguration/azure/mgmt/appconfiguration
+```
+``` yaml $(python-mode) == 'create'
+python:
+  basic-setup-py: true
+  output-folder: $(python-sdks-folder)/appconfiguration/azure-mgmt-appconfiguration
+basic-setup-py: true
+output-folder: $(python-sdks-folder)/appconfiguration/azure-mgmt-appconfiguration
+```
+~~~
+
+## Multi-API
+Multi-API SDK is a package that support multiple REST api-versions. With Python multi-api SDK, the end user can assign api-version for REST calls explicitly; nevertheless, they can also use the default api-version which is choosed as the latest stable api-version.
+
+If a multi-api package is need to be released, 'batch' should be used in the readme.python.md.
+Typical multi-api RPs are azure-mgmt-compute, azure-mgmt-network, azure-mgmt-storage, you cam find their readme files to have a reference for multi-api.
+
+### batch
+The batch is a tag list which are used in the multi-api package. For example:
+~~~
+// file: readme.python.md
+
+### Python multi-api
+
+Generate all API versions currently shipped for this package
+
+```yaml $(multiapi) && !$(track2)           // For track1
+batch:
+  - tag: package-2020-06-01-only
+  - tag: package-2020-05-01-only
+```
+
+```yaml $(multiapi) && $(track2)            // For track2
+clear-output-folder: true
+batch:
+  - tag: package-2020-06-01-only
+  - tag: package-2020-05-01-only
+  - multiapiscript: true
+```
+
+``` yaml $(multiapiscript)                  // For track2
+output-folder: $(python-sdks-folder)/compute/azure-mgmt-compute/azure/mgmt/compute/
+clear-output-folder: false
+perform-load: false
+```
+~~~
+
+### tags of batch
+Then, the output folder and namespace should be configured for each of the tag. For example:
+~~~
+// file: readme.python.md
+
+### Tag: package-2020-06-01-only and python
+
+These settings apply only when `--tag=package-2020-06-01-only --python` is specified on the command line.
+Please also specify `--python-sdks-folder=<path to the root directory of your azure-sdk-for-python clone>`.
+
+``` yaml $(tag) == 'package-2020-06-01-only'
+namespace: azure.mgmt.compute.v2020_06_01
+output-folder: $(python-sdks-folder)/compute/azure-mgmt-compute/azure/mgmt/compute/v2020_06_01
+python:
+  namespace: azure.mgmt.compute.v2020_06_01
+  output-folder: $(python-sdks-folder)/compute/azure-mgmt-compute/azure/mgmt/compute/v2020_06_01
+```
+~~~
+
+
+### multi-api init script
+For track1, multi-api init script need to be configured in readme.md. For example:
+
+~~~
+// file: readme.md
+
+swagger-to-sdk:
+  - repo: azure-sdk-for-python
+    after_scripts:
+      - python ./scripts/multiapi_init_gen.py azure-mgmt-compute
+~~~
+
+
+## Run codegen
+After configure all the readme files, autorest can be used to generate SDK.
+
+### Track1 (for Autorest V2)
+Track1 SDK is based on AutoRest version V2 that's going to be replaced by version V3.
+
+~~~
+autorest --keep-version-file --multiapi --no-async --python --python-mode=update --python-sdks-folder=C:\ZZ\projects\codegen\azure-sdk-for-python\sdk --use=@microsoft.azure/autorest.python@~4.0.71 --version=V2 ..\azure-rest-api-specs\specification\appconfiguration\resource-manager\readme.md
+~~~
+
+### Track2 (for latest Autorest)
+Track 2 is based on the latest AutoRest code generator
+
+~~~
+autorest --python --track2 --use=@autorest/python@5.1.0-preview.4 --python-sdks-folder=..\azure-sdk-for-python\sdk --multiapi --python-mode=update  ..\azure-rest-api-specs\specification\appconfiguration\resource-manager\readme.md
+~~~