Ryan Lane: Text replace - "NOTOC" to ""

2013-02-17T23:30:52Z

Text replace - "__NOTOC__" to ""

Brian at 20:05, 1 February 2011

2011-02-01T20:05:46Z

New page

__NOTOC__

<pre><nowiki>#!wiki caution
'''This is a coding standard ''suggestion''.'''

Relevant blueprint: https://blueprints.launchpad.net/nova
</nowiki></pre>

Certain more nuanced aspects of programming in Python are not covered by PEP-0008. One of those nuances is the use of a keyword arguments helper when confronted with a large number of potential inputs to a function.

For example, a very important and key aspect of creating a virtual server:

<pre><nowiki>#!highlight python
def create(self, context, instance_type,
image_id, kernel_id=None, ramdisk_id=None,
min_count=1, max_count=1,
display_name='', display_description='',
key_name=None, key_data=None, security_group='default',
availability_zone=None, user_data=None):
"""Create the number of instances requested if quota and
other arguments check out ok."""
</nowiki></pre>

Might be rewritten as:

<pre><nowiki>#!highlight python
def create(self, context, instance_type, image_id, **kwargs):
"""
Attempt to create one or more virtual machine instances using the
given context, instance_type, image_id, and a list of parameter which
are passed in as keyword arguments.

`quota.QuotaError` will be raised by this function if the minimum number
of instances cannot be created due to quota violations.

@param context: `nova.context.RequestContext` compatible object
@param instance_type: string identifying the instance type
@param image_id: integer identifying the image to use
@kwarg kernel_id: integer identifying the kernel to use
@kwarg ramdisk_id: integer identifying the ramdisk to use
@kwarg min_count: minimum instances to create, defaults to 1
@kwarg max_count: maximum instances to create, defaults to 1
@kwarg display_name: string name to give created instances
@kwarg display_description: string description to give instances
@kwarg key_name: string name of key pair to use
@kwarg key_data: public key to use for created instances
@kwarg security_group: list or string containing names of groups
@kwarg availability_zone: string identifying availability zone
@kwarg user_data: string of data to attach to created instances
"""
kernel_id = kwargs.get("kernel_id", None)
ramdisk_id = kwargs.get("ramdisk_id", None)
min_count = kwargs.get("min_count", 1)
max_count = kwargs.get("max_count", 1)
display_name = kwargs.get("display_name", "")
display_description = kwargs.get("display_description", "")
key_name = kwargs.get("key_name", None)
security_group = kwargs.get("security_group", "default")
availability_zone = kwargs.get("availability_zone", None)
user_data = kwargs.get("user_data", None)
</nowiki></pre>

'''Why might we want to replace existing code (which works) with code which is ''over 4 times'' as long?'''

# Currently programs like ''pydoc'' are throughly unhelpful when functions such as this one are encountered.
# Function definitions which might have an arbitrary number of keyword parameters can still be made to fit on a smaller number of lines.
# Moving to the new form would allow more fined grained configuration for default values:

<pre><nowiki>#!highlight python
kernel_id = kwargs.get("kernel_id", None)
</nowiki></pre>

...might become...

<pre><nowiki>#!highlight python
kernel_id = kwargs.get("kernel_id", config.default_kernel_id)
</nowiki></pre>

← Older revision		Revision as of 23:30, 17 February 2013
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CodingStandards/KeywordArguments - Revision history

Ryan Lane: Text replace - "__NOTOC__" to ""

Brian at 20:05, 1 February 2011

Ryan Lane: Text replace - "NOTOC" to ""