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# Resource Agent guide for Python
## Introduction
A simple library for authoring resource agents in Python is
provided in the `ocf.py` library.
Agents written in Python should be ideally compatible both with Python
2.7+ and Python 3.3+.
The library provides various helper constants and functions, a logging
implementation as well as a run loop and metadata generation facility.
## Constants
The following OCF constants are provided:
* `OCF_SUCCESS`
* `OCF_ERR_GENERIC`
* `OCF_ERR_ARGS`
* `OCF_ERR_UNIMPLEMENTED`
* `OCF_ERR_PERM`
* `OCF_ERR_INSTALLED`
* `OCF_ERR_CONFIGURED`
* `OCF_NOT_RUNNING`
* `OCF_RUNNING_MASTER`
* `OCF_FAILED_MASTER`
* `OCF_RESOURCE_INSTANCE`
* `HA_DEBUG`
* `HA_DATEFMT`
* `HA_LOGFACILITY`
* `HA_LOGFILE`
* `HA_DEBUGLOG`
* `OCF_ACTION` -- Set to `$__OCF_ACTION` if set, or to the first command line argument.
## Logger
The `logger` variable holds a Python standard log object with its
formatter set to follow the OCF standard logging format.
Example:
``` python
from ocf import logger
logger.error("Something went terribly wrong.")
```
## Helper functions
* `ocf_exit_reason`: Prints the exit error string to stderr.
* `have_binary`: Returns True if the given binary is available.
* `is_true`: Converts an OCF truth value to a Python boolean.
* `get_parameter`: Looks up the matching `OCF_RESKEY_` environment variable.
* `Agent`: Class which helps to generate the XML metadata.
* `run`: OCF run loop implementation.
## Run loop and metadata example
``` python
import os
import sys
OCF_FUNCTIONS_DIR = os.environ.get("OCF_FUNCTIONS_DIR", "%s/lib/heartbeat" % os.environ.get("OCF_ROOT"))
sys.path.append(OCF_FUNCTIONS_DIR)
import ocf
def start_action(argument):
print("The start action receives the argument as a parameter: {}".format(argument))
def main():
agent = ocf.Agent("example-agent",
shortdesc="This is an example agent",
longdesc="An example of how to " +
"write an agent in Python using the ocf " +
"Python library.")
agent.add_parameter("argument",
shortdesc="Example argument",
longdesc="This argument is just an example.",
content_type="string",
default="foobar")
agent.add_action("start", timeout=60, handler=start_action)
agent.run()
if __name__ == "__main__":
main()
```
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