Can be used for less typing, and mobilibility. Not recommanded
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| from .module_name import some_function
from ..module_in_parent_folder import another_fuction
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List attribute names imported via from module import *
Without a init py file under compressed folder import star will get every modules
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| >>> from reader.compressed import * # not recommanded way to import
>>> locals()
{'__name__': '__main__', '__doc__': None, '__package__': None, '__loader__': <class '_frozen_importlib.BuiltinImporter'>, '__spec__': None, '__annotations__': {}, '__builtins__': <module 'builtins' (built-in)>, 'gzipped': <module 'reader.compressed.gzipped' from '/home/vma/decmaxn.github.io/py_pkg/reader/compressed/gzipped.py'>, 'bzipped': <module 'reader.compressed.bzipped' from '/home/vma/decmaxn.github.io/py_pkg/reader/compressed/bzipped.py'>}
>>> bzipped
<module 'reader.compressed.bzipped' from '/home/vma/decmaxn.github.io/py_pkg/reader/compressed/bzipped.py'>
>>> gzipped
<module 'reader.compressed.gzipped' from '/home/vma/decmaxn.github.io/py_pkg/reader/compressed/gzipped.py'>
>>>
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With this py_pkg/reader/compressed/__init__.py , we show only those functions imported to this compressed subpackage, not the modules.
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| from reader.compressed.bzipped import opener as bz2_opener
from reader.compressed.gzipped import opener as gzip_opener
__all__ = ['bz2_opener','gzip_opener']
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Only functions inside __all__ list are imported by import star.
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| >>> locals()
{'__name__': '__main__', '__doc__': None, '__package__': None, '__loader__': <class '_frozen_importlib.BuiltinImporter'>, '__spec__': None, '__annotations__': {}, '__builtins__': <module 'builtins' (built-in)>}
>>> from reader.compressed import *
>>> locals()
{'__name__': '__main__', '__doc__': None, '__package__': None, '__loader__': <class '_frozen_importlib.BuiltinImporter'>, '__spec__': None, '__annotations__': {}, '__builtins__': <module 'builtins' (built-in)>, 'bz2_opener': <function open at 0x7fb534c023a0>, 'gzip_opener': <function open at 0x7fb534b34550>}
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Modules bzipped ang gzipped are just hidden, they call still be imported, just not with import star.
Namespace Packages
special cases when a package is not a folder with init py files, but spread across multiple folders. They are directories with same name located in different paths, which are all put in sys.path.
When you importing a foo package, python looks for:
- foo directory with init py file under it, import if found
- foo.py file, import if found
- all foo folders in sys.path, import all founded.
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| $ mkdir -p path1/foo
$ mkdir -p path2/foo
$ touch path1/foo/m1.py
$ touch path2/foo/m2.py
>>> import sys
>>> sys.path.extend(['path1','path2','path3']) # more pathes in sys.path
>>> import foo
>>> foo.__path__ # 2 folders imported for the same package
_NamespacePath(['/home/vma/decmaxn.github.io/path1/foo', '/home/vma/decmaxn.github.io/path2/foo'])
>>> import foo.m1
>>> foo.m1.__file__ # python find right folder where to import the m1 module
'/home/vma/decmaxn.github.io/path1/foo/m1.py'
>>> import foo.m2
>>> foo.m2.__file__
'/home/vma/decmaxn.github.io/path2/foo/m2.py'
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It’s used to splitting large packages into multiple parts.
There is no init py file, to avoid complex init ordoring problems.
Executable directory
A directory can be executed if there is a __main__.py file.
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| $ ls py_pkg/reader/
__init__.py __pycache__ compressed rdm.py
$ python3 py_pkg/reader
/usr/bin/python3: can't find '__main__' module in 'py_pkg/reader/compressed/'
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Note the readeer.py file has been renamed to rdm.py to avoid a circular import issue casued by the package and module sharing the same name.
After created ``py_pkg/reader/main.py``` like this:
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| import sys
from reader.rdm import Reader
r = Reader(sys.argv[1])
try:
print(r.read())
finally:
r.close()
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It works like a charm.
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| $ python3 py_pkg/reader test.bz2
Content compressed by bz2
$ python3 py_pkg/reader test.gzip
Content compressed by gzip
$ python3 py_pkg/reader LICENSE.md
Copyright (c) 2023 Victor Ma ...
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