How to develop and debug programs that use pyrax or python-novaclient libraries

Python belongs to a category of high-level, dynamically typed programming languages. This has enormous impact on the way how you write the code and how it is interpreted and executed.

As an example let's take a look at Python Rackspace pyrax module. It was built and made available in a form of Python SDK for Rackspace cloud. Under the hood it is a wrapper and integrator of various python libraries that exists to interact with Openstack systems(cloud servers, files, networks, databases ...). As an example it uses python-novaclient library communicate and interact with Nova (Openstack Compute).

From developer point of view you can write a Python program to interact with Rackspace cloud using any of them. Both should work fine.

Working with any of these libraries you are going to face these challenges very soon:

• where is the latest API documentation 
• how well are function documented
• for a function what arguments it accepts and what it returns

In comparison to other statically typed languages like Java you quickly realize that Python definition of a function doesn't' fully answer the above questions. Below are couple of tricks to help you start with to play with them although.

Problem 1

How to start interactive Python session with loaded pyrax module for testing

We are going to use bpython that has a nice feature allowing it to show the available functions and variables a Python objects implements (for these who are interested how this works you can read about introspection here and there)

1. Create a file with credentials

 
root@server:~# cat > rackspace_cloud_credentials
[rackspace_cloud]
username = user
api_key = key



2. Create an auxiliary file for bpython

 
# https://github.com/rtomaszewski/api-challenge/blob/master/bpython-pyrax.py
cat > bpython-pyrax.py
import os
import sys
import json
import re
import time
import datetime, time

from pprint import pprint
from pprint import pformat

import pyrax

creds_file = os.path.expanduser("~/rackspace_cloud_credentials")
pyrax.set_credential_file(creds_file, "LON")
cs = pyrax.cloudservers

help_str="""
the pyrax module has been loaded, try typing one of the commands below to see if it works.

#example 1: whow all cloud servers under you cloud account 
l=cs.servers.list()
print(l)

# example 2: show list of images 
pprint(cs.images.list())
"""

print(help_str)



3. Open the bpython interpreter

 
root@server:~# bpython -i  bpython-pyrax.py

the pyrax module has been loaded, try typing one of the commands below to see if it works.

#example 1: whow all cloud servers under you cloud account
l=cs.servers.list()
print(l)

# example 2: show list of images
pprint(cs.images.list())

>>>



4. Test how it works

Problem 2

How to start interactive Python session with loaded python-novaclient for testing

1. Create bash file with variables

 
cat > nova.vars.sh
export OS_AUTH_SYSTEM="rackspace_uk"
export OS_AUTH_URL="https://lon.identity.api.rackspacecloud.com/v2.0/"
export OS_NO_CACHE="1"
export OS_PASSWORD="pass"
export OS_REGION_NAME="LON"
export OS_TENANT_NAME="user"
export OS_USERNAME="user"
export NOVA_RAX_AUTH=1
export OS_PROJECT_ID="user"



2. Create an auxiliary file for bpython

 
# https://github.com/rtomaszewski/api-challenge/blob/master/bpython-novaclient.py
cat > bpython-novaclient.py
import os
import sys
import json
import re
import time
import datetime, time

from pprint import pprint
from pprint import pformat

from novaclient.v1_1 import client

os.environ["OS_USERNAME"]
os.environ["OS_PASSWORD"]
os.environ["OS_NO_CACHE"]
os.environ["OS_TENANT_NAME"]
os.environ["OS_AUTH_URL"]
os.environ["OS_REGION_NAME"]
os.environ["OS_AUTH_SYSTEM"]
os.environ["NOVA_RAX_AUTH"]
os.environ["OS_PROJECT_ID"]

from novaclient import auth_plugin as _cs_auth_plugin
_cs_auth_plugin.discover_auth_systems()
auth_plugin = _cs_auth_plugin.load_plugin("rackspace_uk")

cs = client.Client(os.environ["OS_USERNAME"], os.environ["OS_PASSWORD"], os.environ["OS_TENANT_NAME"], auth_url=os.environ["OS_AUTH_URL"], auth_system="rackspace", region_name="LON",  service_type="compute", auth_plugin=auth_plugin)

help_str="""
the novaclient module has been loaded and INITIATED, try typing one of the commands below to see if it works.

#example 1: whow all cloud servers under you cloud account 
l=cs.servers.list()
print(l)

# example 2: show list of images 
pprint(cs.images.list())
"""

print(help_str)



3. Open the bpython interpreter

 
root@manage2:~# bpython -i bpython-novaclient.py

the novaclient module has been loaded and INITIATED, try typing one of the commands below to see if it works.

#example 1: whow all cloud servers under you cloud account
l=cs.servers.list()
print(l)

# example 2: show list of images
pprint(cs.images.list())
>>>



4. Test how it works

References

1. http://bpython-interpreter.org/screenshots/
2. http://stackoverflow.com/questions/546337/how-do-i-perform-introspection-on-an-object-in-python-2-x
3. http://docs.rackspace.com/servers/api/v2/cs-gettingstarted/content/section_gs_install_nova.html
4. https://github.com/openstack/python-novaclient
5. https://github.com/rackspace/pyrax/blob/master/samples/cloudservers/create_server.py