Merge pull request hyperledger-indy#917 from telus/py-tutorial3

Add how-tos Python tutorial hyperledger-indy#3

Author: jovfer

doc/how-tos/save-schema-and-cred-def/README.md

@@ -3,4 +3,4 @@
 This shows how to save a schema and credential definition on the ledger, which is
 a prerequisite for ["Issue Credential"](../issue-credential/README.md).
 
-[ [Python](../not-yet-written.md) | [Java](java/README.md) | [.NET](../not-yet-written.md) | [Node.js](../not-yet-written.md) | [Objective C](../not-yet-written.md) ]
+[ [Python](python/README.md) | [Java](java/README.md) | [.NET](../not-yet-written.md) | [Node.js](../not-yet-written.md) | [Objective C](../not-yet-written.md) ]

doc/how-tos/save-schema-and-cred-def/python/README.md

@@ -0,0 +1,103 @@
+# Save a Schema and Credential Definition
+
+Indy-SDK Developer Walkthrough #4, Python Edition
+
+[ [Java](../java/README.md) | [.NET](../../not-yet-written.md) | [Node.js](../../not-yet-written.md) | [Objective C](../../not-yet-written.md) ]
+
+
+## Prerequisites
+
+Setup your workstation with an indy development virtual machine (VM). See [prerequisites](../../prerequisites.md).
+
+Ensure you have the 64-bit version of Python 3 installed, as the 32-bit version may have problems loading the Indy .dll files.
+
+## Steps
+
+### Step 1
+
+In your normal workstation operating system (not the VM), open a Python editor of your
+choice and paste the code from [template.py](template.py)
+into a new doc. We will be modifying this code in later steps.
+
+Save the doc as `save_schema_and_cred_def.py`
+
+This is a very simple app framework into which you'll plug the code you'll be writing.
+
+Install the required python packages by executing: `$ pip install python3-indy asyncio`
+
+### Step 2
+
+We need to give the SDK some context that it will need
+to deal with an indy ledger. This requires us to point the SDK at some
+*genesis transactions* that tell the SDK how to contact the ledger on
+the network and how to trust that the nodes it contacts possess
+appropriate keys. We also need to create a wallet so the SDK can store
+DIDs and the key material we're going to use. Also, we need
+to create a trust anchor identity that has privileges to create schemas
+and credential definitions.
+
+All of these steps are similar to those in simpler how-tos, such as
+["Write a DID and Query Its Verkey"](../../write-did-and-query-verkey/python/readme.md).
+We'll get this housekeeping out of
+the way in a single step here, rather than dwelling on its details.
+
+Copy the contents of [step2.py](step2.py) into
+`save_schema_and_cred_def.py` on top of the `Step 2 code goes here` placeholder comment.
+
+Save the updated version of `save_schema_and_cred_def.py`.
+
+Study the changes. Scaffolding code like this is likely to appear in anything
+that uses indy.
+
+### Step 3
+
+Now we need to create and define a schema. Schemas in indy are very simple
+JSON documents that specify their name and version, and that list attributes
+that will appear in a credential. Today, they do not describe data type,
+recurrence rules, nesting, and other elaborate constructs. There is work
+underway to make them fancier; visit
+[#indy-sdk on Rocket.Chat](https://chat.hyperledger.org/channel/indy-sdk) to learn
+more.
+
+A sample schema might look like this:
+
+```json
+{
+  "id": "1",
+  "name": "gvt",
+  "version": "1.0",
+  "ver': "1.0",
+  "attrNames": ["age", "sex", "height", "name"]
+}
+```
+
+Copy the contents of [step3.py](step3.py) into
+`save_schema_and_cred_def.py` on top of the `Step 3 code goes here` placeholder comment.
+
+Save the updated version of `save_schema_and_cred_def.py`.
+
+Notice how this schema is submitted to the ledger by the steward
+identity we created previously.
+
+### Step 4
+
+Next, we create a *credential definition*. This references the schema
+that we just added, and announces who is going to be issuing credentials
+with that schema (our trust anchor identity, in this case), what type of
+signature method they plan to use ("CL" = "Camenisch Lysyanskya", the
+default method used for zero-knowledge proofs by indy), how they
+plan to handle revocation, and so forth.
+
+Copy the contents of [step4.py](step4.py) into
+`save_schema_and_cred_def.py` on top of the `Step 4 code goes here` placeholder comment.
+
+Save the updated version of `save_schema_and_cred_def.py``.
+
+### Step 5
+
+Run the [finished code](save_schema_and_cred_def.py) and observe the whole sequence.
+
+## More experiments
+
+You might try the ["Issue a Credential"](../../issue-credential/../not-yet-written.md)
+how-to, which can be done in only one step once you complete this one.