prepend_sys_path does not work with absolute paths on windows

Describe the bug

If you put an absolute path in prepend_sys_path in your alembic.ini on windows (which will happen if you use %(here)s), the path will get split on the ':' character that separates the drive letter.

Expected behavior

Absolute paths to not get broken.

To Reproduce
Use an absolute path in prepend_sys_path like C:/something or %(here)s/something

Then print out sys.path, e.g. for path in sys.path: print(path) you get:

C
\something
C
\path\to\here\something

# Insert code here

Error
ModuleNotFoundError: No module named ...
because env.py can't import my modules.

Versions.

OS: Windows 10
Python: 3.11.5
Alembic: 1.12.0
SQLAlchemy: 1.4.49
Database: Postgres
DBAPI: psycopg2

Additional context

alembic/alembic/script/base.py

Lines 212 to 218 in 3e48ed0

    
           prepend_sys_path = config.get_main_option("prepend_sys_path") 
        
           if prepend_sys_path: 
        
               sys.path[:0] = list( 
        
                   _split_on_space_comma_colon.split(prepend_sys_path) 
        
               )

@CaselIT

@CaselIT is this also #1284 ?

PRs with tests welcome here

Improve handling of prepend_sys_path

@CaselIT

@CaselIT is this also #1284 ?

it should not, since that depend on the value of version_path_separator

Proposed in #1331 we add a new config value with legacy fallback behavior as follows:

# sys.path path, will be prepended to sys.path if present.
# defaults to the current working directory.  for multiple paths, the path separator
# is defined by prepend_sys_path_separator
prepend_sys_path = .

# prepend sys path separator; As mentioned above, this is the character used to split
# sys_path paths.  The default within new alembic.ini files is "os", which uses os.pathsep.
# If this key is omitted entirely, it falls back to the legacy behavior of splitting on spaces and/or commas.
# Valid values for prepend_sys_path_separator are:
#
# prepend_sys_path_separator = :
# prepend_sys_path_separator = ;
# prepend_sys_path_separator = space
prepend_sys_path_separator = os  # Use os.pathsep. Default configuration used for new projects.

it's probably the most sensible option. it makes little sense to have the two paths in the config handled in a different way

I guess if we were on pyproject.toml this whole thing would be a non issue since it supports lists :)

does not support %(here)s though

Improve handling of prepend_sys_path

Mike Werezak has proposed a fix for this issue in the main branch:

Improve handling of prepend_sys_path, fixes #1330 https://gerrit.sqlalchemy.org/c/sqlalchemy/alembic/+/5873

Add file_path_separator to apply to all path splitting

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prepend_sys_path does not work with absolute paths on windows #1330

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	prepend_sys_path = config.get_main_option("prepend_sys_path")
	if prepend_sys_path:
	sys.path[:0] = list(
	_split_on_space_comma_colon.split(prepend_sys_path)
	)

prepend_sys_path does not work with absolute paths on windows #1330

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zzzeek commented on Oct 19, 2023

zzzeek commented on Oct 19, 2023

CaselIT commented on Oct 19, 2023

zzzeek commented on Oct 19, 2023

CaselIT commented on Oct 19, 2023

zzzeek commented on Oct 19, 2023

CaselIT commented on Oct 19, 2023

sqla-tester commented on Apr 26, 2025

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