Enforce version constraint and clarify ubuntu install (#109)

docs/source/getting-started.rst

@@ -9,13 +9,22 @@ Install Dependencies
 --------------------
 BinaryAlert can be deployed from any MacOS/Linux environment (and likely Windows as well, though we haven't tried).
 
-1. Install `Python 3.6 <https://www.python.org/downloads/release/python-362>`_:
+1. Install `Python 3.6 <https://www.python.org/downloads/release/python-364/>`_:
 
 .. code-block:: bash
 
-  $ brew install python3  # MacOS Homebrew
-  $ sudo apt-get install python3.6  # Ubuntu 16+
-  $ python3 --version  # Should show 3.6.x
+  # MacOS Homebrew
+  brew install python3
+  python3 --version
+
+  # Ubuntu16 - Python 3.6 is only available in third-party repositories
+  sudo add-apt-repository ppa:deadsnakes/ppa
+  sudo apt-get update
+  sudo apt-get install python3.6 python3.6-dev python3-pip
+  sudo -H pip3 install --upgrade pip
+  python3.6 --version
+
+.. warning:: Python 3.5 is installed by default on some systems, but BinaryAlert requires Python 3.6.
 
 2. Install `Terraform <https://www.terraform.io/downloads.html>`_ v0.11.X:
 
@@ -28,7 +37,7 @@ BinaryAlert can be deployed from any MacOS/Linux environment (and likely Windows
 
 .. code-block:: bash
 
-  $ pip3 install virtualenv
+  $ sudo -H pip3 install virtualenv
   $ virtualenv --version
 
 4. Install the OpenSSL development library if it isn't already (OS X should have it).
@@ -40,29 +49,6 @@ and must be installed *before* installing the BinaryAlert requirements.
   $ sudo apt-get install libssl-dev  # Ubuntu
   $ sudo yum install openssl-devel   # Amazon Linux
 
-Set AWS Credentials
--------------------
-1. Create an AWS account and an IAM user with permissions for at least the following services:
-
-  * CloudWatch
-  * DynamoDB
-  * IAM
-  * KMS
-  * Lambda
-  * S3
-  * SNS
-  * SQS
-
-.. note:: See `Creating an IAM group <iam-group.html>`_ for a least-privilege policy that allows users to deploy BinaryAlert.
-
-2. Set your AWS credentials using `any method supported by Terraform <https://www.terraform.io/docs/providers/aws/#authentication>`_.
-For example, using the AWS CLI:
-
-.. code-block:: bash
-
-  $ pip3 install awscli
-  $ aws configure
-
 
 Download BinaryAlert
 --------------------
@@ -77,7 +63,7 @@ Download BinaryAlert
 .. code-block:: bash
 
   $ cd binaryalert
-  $ virtualenv -p python3 venv
+  $ virtualenv -p python3.6 venv
   $ source venv/bin/activate
 
 3. Install the BinaryAlert requirements:
@@ -94,6 +80,28 @@ Download BinaryAlert
 
   $ ./manage.py unit_test
 
+Set AWS Credentials
+-------------------
+1. Create an AWS account and an IAM user with permissions for at least the following services:
+
+  * CloudWatch
+  * DynamoDB
+  * IAM
+  * KMS
+  * Lambda
+  * S3
+  * SNS
+  * SQS
+
+.. note:: See `Creating an IAM group <iam-group.html>`_ for a least-privilege policy that allows users to deploy BinaryAlert.
+
+2. Set your AWS credentials using `any method supported by Terraform <https://www.terraform.io/docs/providers/aws/#authentication>`_.
+For example, using the AWS CLI:
+
+.. code-block:: bash
+
+  $ pip3 install awscli
+  $ aws configure
 
 Deploy!
 -------

manage.py

@@ -468,6 +468,11 @@ def unit_test() -> None:
 
 def main() -> None:
     """Main command dispatcher."""
+    if sys.version_info < (3, 6):
+        print('ERROR: Python 3.6+ is required, found Python {}.{}.{}'.format(
+            sys.version_info.major, sys.version_info.minor, sys.version_info.micro))
+        exit(1)
+
     manager = Manager()
 
     parser = argparse.ArgumentParser(formatter_class=argparse.RawTextHelpFormatter)