IndendationError from multi-line indented statements

[ucodery]

BPO	46091
Nosy	@gvanrossum, @lysnikolaou, @pablogsal, @ucodery
PRs	bpo-46091: Correctly calculate indentation levels for whitespace lines with continuation characters #30130 [3.10] bpo-46091: Correctly calculate indentation levels for whitespace lines with continuation characters (GH-30130). #30898 [3.9] bpo-46091: Correctly calculate indentation levels for whitespace lines with continuation characters (GH-30130). (GH-30898) #30899
Files	nodent.py: example program where every indented line also uses ''

^{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 2022-01-25.22:38:52.006>
created_at = <Date 2021-12-15.23:06:30.736>
labels = ['interpreter-core', '3.9', '3.10', '3.11']
title = 'IndendationError from multi-line indented statements'
updated_at = <Date 2022-01-25.22:38:52.005>
user = 'https://github.com/ucodery'

bugs.python.org fields:

activity = <Date 2022-01-25.22:38:52.005>
actor = 'pablogsal'
assignee = 'none'
closed = True
closed_date = <Date 2022-01-25.22:38:52.006>
closer = 'pablogsal'
components = ['Parser']
creation = <Date 2021-12-15.23:06:30.736>
creator = 'ucodery'
dependencies = []
files = ['50496']
hgrepos = []
issue_num = 46091
keywords = ['patch']
message_count = 7.0
messages = ['408651', '408654', '408656', '408661', '408663', '411678', '411680']
nosy_count = 4.0
nosy_names = ['gvanrossum', 'lys.nikolaou', 'pablogsal', 'ucodery']
pr_nums = ['30130', '30898', '30899']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue46091'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

[ucodery]

At some point in 3.9 Python appears to have stopped accepting source that starts with an indent, then a '\', then the indented statement. From the lexical analysis 1 "Indentation cannot be split over multiple physical lines using backslashes; the whitespace up to the first backslash determines the indentation."

Running the attached program under 3.8.12 I get:

0 1 1 2 3 5 8 13 21 34 55 89 144 233 377

But running under 3.10.0 I get:

  File "/Users/jeremyp/tmp/nodent.py", line 3
    """Print a Fibonacci series up to n."""
    ^
IndentationError: expected an indented block after function definition on line 1

Running under 3.9.9 also gives an IndentationError, both with and without -X oldparser. So this doesn't seem directly related to the new parser, but seems likely it is fall out from the general grammar restructuring.

IMHO it isn't a particularly nice feature for the language to have. Especially since not all lines like ' \' behave the same. But it was there and documented for many years, so should probably be put back. Does a core developer agree? That the implementation is not following the spec?

[pablogsal]

This is a side effect on the fix in:

https://bugs.python.org/issue40847

[pablogsal]

Unfortunately I am not sure if this is going to be easier to retrofit for the reasons exposed in the issue. I will try to take a look, but if you have some cycles to spare, a PR would be welcomed.

[pablogsal]

nevermind, I am convinced is a bug. I filed a PR for it

[ucodery]

Wow, this was a fast turnaround! I was going to spin some cycles on this, but would have not seen the solution in 50m.

[pablogsal]

New changeset a0efc0c by Pablo Galindo Salgado in branch 'main':
bpo-46091: Correctly calculate indentation levels for whitespace lines with continuation characters (GH-30130)
a0efc0c

[pablogsal]

New changeset 3fc8b74 by Pablo Galindo Salgado in branch '3.10':
[3.10] bpo-46091: Correctly calculate indentation levels for whitespace lines with continuation characters (GH-30130). (GH-30898)
3fc8b74