Add PyBuffer_SizeFromFormat() C helper for struct.calcsize()

[ellerynewcomer]

BPO	15913
Nosy	@vstinner
PRs	bpo-15913 : Add PyBuffer_SizeFromFormat() #13873

^{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 2019-08-20.14:47:47.638>
created_at = <Date 2012-09-10.21:27:23.623>
labels = ['interpreter-core', 'type-feature', '3.9']
title = 'Add PyBuffer_SizeFromFormat() C helper for struct.calcsize()'
updated_at = <Date 2019-08-20.14:47:47.637>
user = 'https://bugs.python.org/ellerynewcomer'

bugs.python.org fields:

activity = <Date 2019-08-20.14:47:47.637>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2019-08-20.14:47:47.638>
closer = 'vstinner'
components = ['Interpreter Core']
creation = <Date 2012-09-10.21:27:23.623>
creator = 'ellery.newcomer'
dependencies = []
files = []
hgrepos = []
issue_num = 15913
keywords = ['patch']
message_count = 4.0
messages = ['170239', '170269', '350007', '350008']
nosy_count = 2.0
nosy_names = ['vstinner', 'ellery.newcomer']
pr_nums = ['13873']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue15913'
versions = ['Python 3.9']

[ellerynewcomer]

this function is listed in the buffer docs and in abstract.h, but there is no implementation anywhere.

[skrah]

Even though it's documented, the function is probably a new feature
and should go into 3.4.

Meanwhile, you can call struct.calcsize(format). Any non-trivial
implementation of PyBuffer_SizeFromFormat() would likely do the same.

[vstinner]

New changeset 9e66aba by Victor Stinner (Joannah Nanjekye) in branch 'master':
bpo-15913: Implement PyBuffer_SizeFromFormat() (GH-13873)
9e66aba

[vstinner]

Joannah Nanjekye implemented the function, thanks.