Python importing a sub-package or sub-module

Question

Having already use flat packages  I was not expecting the issue I encountered with nested packages  Here is     Directory layout  dir      -- test py      -- package                --   init   py                -- subpackage                          --   init   py                          -- module py   Content of init py  Both package   init   py and package subpackage   init   py are empty   Content of module py    file  package subpackage module py  attribute1    value 1  attribute2    value 2  attribute3    value 3    and as many more as you want      Content of test py  3 versions   Version 1    file test py from package subpackage module import   print attribute1   OK   That s the bad and unsafe way of importing things  import all in a bulk   but it works   Version 2    file test py import package subpackage module from package subpackage import module   Alternative from module import attribute1   A safer way to import  item by item  but it fails  Python don t want this  fails with the message   No module named module   However         file test py import package subpackage module from package subpackage import module   Alternative print module   Surprise here        says  lt module  package subpackage module  from       gt   So that s a module  but that s not a module  -P 8-O     uh  Version 3    file test py v3 from package subpackage module import attribute1 print attribute1   OK   This one works  So you are either forced to use the overkill prefix all the time or use the unsafe way as in version  1 and disallowed by Python to use the safe handy way  The better way  which is safe and avoid unecessary long prefix is the only one which Python reject  Is this because it loves import   or because it loves overlong prefixes  which does not help to enforce this practice     Sorry for the hard words  but that s two days I trying to work around this stupid-like behavior  Unless I was totally wrong somewhere  this will leave me with a feeling something is really broken in Python s model of package and sub-packages   Notes    I don t want to rely on sys path  to avoid global side effects  nor on   pth files  which are just another way to play with sys path with the same global effets  For the solution to be clean  it has to be local only  Either Python is able to handle subpackage  either it s not  but it should not require to play with global configuration to be able to handle local stuff  I also tried use imports in package subpackage   init   py  but it solved nothing  it do the same  and complains subpackage is not a known module  while print subpackage says it s a module  weird behavior  again     May be I m entirely wrong tough  the option I would prefer   but this make me feel a lot disappointed about Python   Any other known way beside of the three I tried  Something I don t know about    sigh   -----   lt  ----- edit -----    -----  Conclusion so far  after people s comments   There is nothing like real sub-package in Python  as all package references goes to a global dictionnary  only  which means there s no local dictionary  which implies there s is no way to manage local package reference   You have to either use full prefix or short prefix or alias  As in   Full prefix version  from package subpackage module import attribute1   An repeat it again an again   But after that  you can simply  use of  attribute1    Short prefix version  but repeated prefix   from package subpackage import module   Short but then you have to do  use of  module attribute1    and repeat the prefix at every use place   Or else  a variation of the above   from package subpackage import module as m use of  m attribute1     m  is a shorter prefix  but you could as well   define a more meaningful name after the context   Factorized version  If you don t mind about importing multiple entity all at once in a batch  you can   from package subpackage module import attribute1  attribute2   and etc    Not in my first favorite taste  I prefer to have one import statement per imported entity   but may be the one I will personally favor   Update  2012-09-14    Finally appears to be OK in practice  except with a comment about the layout  Instead of the above  I used   from package subpackage module import        attribute1       attribute2      attribute3              and etc

User · Accepted Answer

You seem to be misunderstanding how import searches for modules   When you use an import statement it always searches the actual module path  and or sys modules   it doesn t make use of module objects in the local namespace that exist because of previous imports   When you do   import package subpackage module from package subpackage import module from module import attribute1   The second line looks for a package called package subpackage and imports module from that package   This line has no effect on the third line   The third line just looks for a module called module and doesn t find one   It doesn t  re-use  the object called module that you got from the line above   In other words from someModule import     doesn t mean  from the module called someModule that I imported earlier     it means  from the module named someModule that you find on sys path       There is no way to  incrementally  build up a module s path by importing the packages that lead to it   You always have to refer to the entire module name when importing   It s not clear what you re trying to achieve   If you only want to import the particular object attribute1  just do from package subpackage module import attribute1 and be done with it   You need never worry about the long package subpackage module once you ve imported the name you want from it   If you do want to have access to the module to access other names later  then you can do from package subpackage import module and  as you ve seen you can then do module attribute1 and so on as much as you like   If you want both --- that is  if you want attribute1 directly accessible and you want module accessible  just do both of the above   from package subpackage import module from package subpackage module import attribute1 attribute1   works module someOtherAttribute   also works   If you don t like typing package subpackage even twice  you can just manually create a local reference to attribute1   from package subpackage import module attribute1   module attribute1 attribute1   works module someOtherAttribute  also works

User · Answer

The reason  2 fails is because sys modules  module   does not exist  the import routine has its own scope  and cannot see the module local name   and there s no module module or package on-disk  Note that you can separate multiple imported names by commas   from package subpackage module import attribute1  attribute2  attribute3   Also   from package subpackage import module print module attribute1

User · Answer

If all you re trying to do is to get attribute1 in your global namespace  version 3 seems just fine   Why is it overkill prefix    In version 2  instead of  from module import attribute1   you can do  attribute1   module attribute1

[python] Python: importing a sub-package or sub-module

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