Allow urllib.request.Request subclasses to override method

[jaraco]

BPO	18978
Nosy	@jaraco, @orsenthil
Files	6d6d68c068ad.diff 2b2744cfb08f.diff 061eb75339e2.diff

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2013-09-22.14:11:15.600>
created_at = <Date 2013-09-08.16:41:28.700>
labels = ['library']
title = 'Allow urllib.request.Request subclasses to override method'
updated_at = <Date 2014-02-25.15:23:30.204>
user = 'https://github.com/jaraco'

bugs.python.org fields:

activity = <Date 2014-02-25.15:23:30.204>
actor = 'python-dev'
assignee = 'none'
closed = True
closed_date = <Date 2013-09-22.14:11:15.600>
closer = 'python-dev'
components = ['Library (Lib)']
creation = <Date 2013-09-08.16:41:28.700>
creator = 'jaraco'
dependencies = []
files = ['31676', '31677', '31678']
hgrepos = ['208']
issue_num = 18978
keywords = ['patch']
message_count = 8.0
messages = ['197281', '197283', '197284', '197288', '198278', '198280', '198551', '212184']
nosy_count = 3.0
nosy_names = ['jaraco', 'orsenthil', 'python-dev']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue18978'
versions = ['Python 3.4']

[jaraco]

In Python 2.x and 3.2, I used to use a Request subclass I created for overriding the method used:

class MethodRequest(request.Request):
	def __init__(self, *args, **kwargs):
		"""
		Construct a MethodRequest. Usage is the same as for
		`urllib.request.Request` except it also takes an optional `method`
		keyword argument. If supplied, `method` will be used instead of
		the default.
		"""
		if 'method' in kwargs:
			self.method = kwargs.pop('method')
		return request.Request.__init__(self, *args, **kwargs)

	def get_method(self):
		return getattr(self, 'method', request.Request.get_method(self))

In Python 3.3, which now supports a method parameter, it broke this paradigm (because the method is stored in the instance and is always set to None in __init__ if not specified).

I believe a paradigm where the method is stored as a class attribute and possibly overridden in an instance would be much better, allowing for subclasses to simply and directly override the method. For example:

class HeadRequest(MethodRequest):
	method = 'HEAD'

That straightforward example works very well if method is allowed to be a class attribute, but won't work at all if 'method' is always set as an instance attribute in __init__.

And while it's possible for HeadRequest to override __init__, that requires HeadRequest to override that entire signature, which is less elegant than simply setting a class attribute.

For Python 3.4, I'd like to adapt the Request class to allow the Method to be defined at the class level (while still honoring customization at the instance level).

[orsenthil]

Hi Jason,

Agree with you. This design change could be valuable in extending urllib.request.Request

Thanks!

[jaraco]

I've created a clone in which to draft this work.

[jaraco]

I've added tests to capture the new behavior.

[python-dev]

New changeset 6d6d68c068ad by Jason R. Coombs in branch 'default':
Issue bpo-18978: Allow Request.method to be defined at the class level.
http://hg.python.org/cpython/rev/6d6d68c068ad

New changeset 2b2744cfb08f by Jason R. Coombs in branch 'default':
Issue bpo-18978: A more elegant technique for resolving the method
http://hg.python.org/cpython/rev/2b2744cfb08f

New changeset 061eb75339e2 by Jason R. Coombs in branch 'default':
Issue bpo-18978: Add tests to capture expected behavior for class-level method overrides.
http://hg.python.org/cpython/rev/061eb75339e2

New changeset 8620aea9bbca by Jason R. Coombs in branch 'default':
Close bpo-18978: Merge changes.
http://hg.python.org/cpython/rev/8620aea9bbca

[python-dev]

New changeset 7f13d5ecf71f by Jason R. Coombs in branch 'default':
Issue bpo-18978: Update docs to reflect explicitly the ability to set the attribute at the class level.
http://hg.python.org/cpython/rev/7f13d5ecf71f

[orsenthil]

Thanks for the this change, Jason. Docs could be updated to reflect this change (using ..versionchanged: directive). Thank you!

[python-dev]

New changeset 1afbd851d1c1 by R David Murray in branch 'default':
whatsnew: Request.method can be overridden in subclasses (bpo-18978).
http://hg.python.org/cpython/rev/1afbd851d1c1