Better error messages for wsgiref validator failures

[f80b24cc-32aa-43d3-b7a7-c241e07eb45f]

BPO	14652
Nosy	@berkerpeksag, @Sidnicious
Files	ssm_validate.patch ssm_validate.patch: Don’t use tuples when using only len() to format a string issue14652.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: ```python assignee = None closed_at = None created_at = labels = ['type-feature', 'library'] title = 'Better error messages for wsgiref validator failures' updated_at = user = 'https://github.com/Sidnicious' ``` bugs.python.org fields: ```python activity = actor = 'berker.peksag' assignee = 'none' closed = False closed_date = None closer = None components = ['Library (Lib)'] creation = creator = 'ssm' dependencies = [] files = ['25320', '25624', '38131'] hgrepos = [] issue_num = 14652 keywords = ['patch'] message_count = 4.0 messages = ['159053', '160951', '160971', '235914'] nosy_count = 3.0 nosy_names = ['mcjeff', 'berker.peksag', 'ssm'] pr_nums = [] priority = 'normal' resolution = None stage = 'patch review' status = 'open' superseder = None type = 'enhancement' url = 'https://bugs.python.org/issue14652' versions = ['Python 3.4', 'Python 3.5'] ```

[f80b24cc-32aa-43d3-b7a7-c241e07eb45f]

wsgiref’s validation middleware is missing messages for many of its assertions, and its docstring doesn’t reflect read() now requiring an argument (said that it took an optional argument).

Here’s a patch to add some and update the comment.

[8c8022e7-f081-4d49-be03-926cedb53a7a]

I went through the patch real quick and I noticed that your using single element tuples in your string formatting. That makes sense in situations where the argument might itself be a tuple, however, not on calls to len() as that will return an integer.

[f80b24cc-32aa-43d3-b7a7-c241e07eb45f]

Thanks Jeff, I’m actually a relatively new Python developer and got the impression that it was best practice to always use a tuple for string formatting, for consistency.

Here’s an updated patch which drops the tuples for those cases.

[berkerpeksag]

Here is an updated patch. For InputWrapper.read(), see bpo-18610.