importloc

Import Python objects from arbitrary locations specified by string.

Features

• Minimalistic fully typed package
• Import from files or named modules
• Import deeply nested objects
• Import all instances or all subclasses
• Configurable module name conflict resolution
• Atomicity: on import error, new module is removed, and previous, if any, is restored

Installation

$ pip install importloc

Usage

• Various locations
  • Import from file
  • Import from module
  • Distinguish file and module locations
• Various targets
  • Import nested class
  • Import module as a whole
  • Use Path object when loading module
  • Import all instances of some type
  • Import all subclasses
• Custom module name
  • Use different module name
  • Generate module name at run time
• What if module is already imported?
  • Module name conflict raises error by default
  • Reuse module that is already imported
  • Reload module that is already imported
  • Replace old module with imported one
  • Load module under different generated name
  • Combine override and rename
• What if object does not exist?
  • Missing object causes AttributeError

Quick start

The main and most used entity is Location.

from importloc import Location

Various locations

Import from file

Location('app/config.py:conf').load()

Example

>>> loc = Location('app/config.py:conf')
>>> loc
<PathLocation 'app/config.py' obj='conf'>
>>> loc.load()
<config.Config object at 0x...>

Import from module

Location('app.__main__:cli').load()

Example

>>> loc = Location('app.__main__:cli')
>>> loc
<ModuleLocation 'app.__main__' obj='cli'>
>>> loc.load()
<function cli at 0x...>

Distinguish file and module locations

Location('./config.py:conf').load()

Example

>>> loc = Location('config.py:conf')
>>> loc
<ModuleLocation 'config.py' obj='conf'>
>>> loc.load()
Traceback (most recent call last):
    ...
ModuleNotFoundError: No module named 'config.py'...

Use relative path (similar to Docker bind mount). Path separator will result in PathLocation instead of ModuleLocation.

>>> loc = Location('./config.py:conf')
>>> loc
<PathLocation 'config.py' obj='conf'>
>>> loc.load()
<config.Config object at 0x...>

Various targets

Import nested class

Location('app/config.py:Config.Nested').load()

Example

>>> loc = Location('app/config.py:Config.Nested')
>>> loc
<PathLocation 'app/config.py' obj='Config.Nested'>
>>> loc.load()
<class 'config.Config.Nested'>

Import module as a whole

Location('app/config.py').load()

Example

>>> loc = Location('app/config.py')
>>> loc
<PathLocation 'app/config.py'>
>>> loc.load()
<module 'config' from '...'>

Use Path object when loading module

Location(Path('config.py')).load()

Example

>>> from pathlib import Path
>>> loc = Location(Path('config.py'))
>>> loc
<PathLocation 'config.py'>
>>> loc.load()
<module 'config' from '...'>

Import all instances of some type

get_instances(Location('app.__main__').load(), Callable)

Example

>>> from collections.abc import Callable
>>> from importloc import get_instances
>>> loc = Location('app.__main__')
>>> loc
<ModuleLocation 'app.__main__'>
>>> get_instances(loc.load(), Callable)
[<function cli at 0x...>]

Import all subclasses

get_subclasses(Location('app.errors').load(), Exception)

Example

>>> from importloc import get_subclasses
>>> loc = Location('app.errors')
>>> loc
<ModuleLocation 'app.errors'>
>>> get_subclasses(loc.load(), Exception)
[<class 'app.errors.Error1'>, <class 'app.errors.Error2'>]

Custom module name

Use different module name

Location('...').load(modname='app_main')

Example

>>> Location('app/config.py:Config').load(modname='app_main')
<class 'app_main.Config'>

Generate module name at run time

Location('...').load(modname=random_name)

Example

>>> from importloc import random_name
>>> Location('app/config.py:Config').load(modname=random_name)
<class 'u....Config'>

What if module is already imported?

The module name conflict can be resolved with one the methods:

• reuse existing module imported before
• reload existing module
• replace existing module
• rename new module (try to import under new name)
• raise exception (default)

For details, see documentation on ConflictResolution.

Module name conflict raises error by default

Location('...').load()

Example

>>> Location('app/config.py:Config').load()
<class 'config.Config'>
>>> Location('app/config.py:Config').load()
Traceback (most recent call last):
    ...
importloc.exc.ModuleNameConflict: Module "config" is already imported

Reuse module that is already imported

Location('...').load(on_conflict='reuse')

Example

>>> C = Location('app/config.py:Config').load()
>>> C
<class 'config.Config'>
>>> old_id = id(C)
>>> C = Location('app/config.py:Config').load(on_conflict='reuse')
>>> C
<class 'config.Config'>
>>> # C is the same object:
>>> id(C) == old_id
True

Reload module that is already imported

Location('...').load(on_conflict='reload')

Example

>>> import sys
>>> C = Location('app/config.py:Config').load()
>>> C
<class 'config.Config'>
>>> old_id = id(C)
>>> mod_id = id(sys.modules['config'])
>>> C = Location('app/config.py:Config').load(on_conflict='reload')
>>> C
<class 'config.Config'>
>>> # module object remains the same after reloading:
>>> id(sys.modules['config']) == mod_id
True
>>> # C is the new object from reloaded module:
>>> id(C) == old_id
False

Replace old module with imported one

Location('...').load(on_conflict='replace')

Example

>>> import sys
>>> C = Location('app/config.py:Config').load()
>>> C
<class 'config.Config'>
>>> mod_id = id(sys.modules['config'])
>>> C = Location('app/config.py:Config').load(on_conflict='replace')
>>> C
<class 'config.Config'>
>>> # module object is the new one:
>>> id(sys.modules['config']) == mod_id
False

Load module under different generated name

Location('...').load(on_conflict='rename', rename=random_name)

Example

>>> from importloc import random_name
>>> Location('app/config.py').load()
<module 'config' from ...>
>>> Location('app/config.py').load(on_conflict='rename', rename=random_name)
<module 'u...'>

Combine override and rename

Location('...').load(modname='...', on_conflict='rename', rename=random_name)

Example

>>> from importloc import random_name
>>> Location('app/config.py').load(modname='app_config')
<module 'app_config' from ...>
>>> Location('app/config.py').load(
...     modname='app_config', on_conflict='rename', rename=random_name
... )
<module 'u...' from ...>

What if object does not exist?

Missing object causes AttributeError

When module was imported but requested object does not exist, AttributeError is raised.

Example

>>> Location('app/config.py:unknown').load()
Traceback (most recent call last):
    ...
AttributeError: object has no attribute 'unknown'
>>> # due to import atomicity, module 'config' was removed
>>> import sys
>>> 'config' in sys.modules
False

See also

• Similar implementations
• Project changelog