Do I need to import submodules directly?

by

If I want to use a method in foo.bar, do I need to import foo.bar directly or is importing foo sufficient?

You’ll need to import the submodule explicitly. Executing import foo.bar will automatically import the parent module foo, and necessarily† bind the name foo, but the reverse is not true.

But I could have sworn I’ve seen code where it’s not imported directly and still works fine

Yes. Sometimes accessing a submodule works without the explicit import. This happens when a parent module itself imports the submodules. Never rely on that unless it’s documented, because it may be an implementation detail and could change without warning after a library version upgrade.

As an example of a popular library which demonstrates both behaviors, look at requests==2.18.4. This package has submodules called sessions and help (amongst others). Importing requests will make requests.sessions available implicitly, yet requests.help will not be available until explicitly imported. You’ll find when the source code of the package init is executed that the sessions submodule gets imported, but the help submodule does not.

† This makes sense, because subsequent use of foo.bar requires an attribute access on an existing foo object. Note that from foo.bar import something does not bind the name foo nor foo.bar, though both modules foo and foo.bar are imported and cached into sys.modules.

More Related Contents:

  1. Does Python IDE have a module which imports math functions such as cos or sin? [closed]
  2. Relative imports for the billionth time
  3. How to avoid circular imports in Python? [duplicate]
  4. Importing variables from another file?
  5. In python, how to import filename starts with a number
  6. Expand Python Search Path to Other Source
  7. How to import members of all modules within a package?
  8. Importing from a relative path in Python
  9. Modules are installed using pip on OSX but not found when importing
  10. Why do circular imports seemingly work further up in the call stack but then raise an ImportError further down?
  11. How do I call a function from another .py file?
  12. How to access a standard-library module in Python when there is a local module with the same name?
  13. import text to pandas with multiple delimiters
  14. PyCharm import external library
  15. What does “Symbol not found / Expected in: flat namespace” actually mean?
  16. numpy.genfromtxt produces array of what looks like tuples, not a 2D array—why?
  17. Python import mechanics
  18. pytest cannot import module while python can
  19. Split models.py into several files
  20. Difference between import tkinter as tk and from tkinter import
  21. how to test if one python module has been imported?
  22. importing a module in nested packages
  23. Alternative to execfile in Python 3? [duplicate]
  24. Import Python Script Into Another?
  25. Importing a function from a class in another file? [duplicate]
  26. How do I override a Python import?
  27. How to stop another already running script in python?
  28. Read Tables from pdf using python [duplicate]
  29. using import inside class
  30. How to use the __import__ function to import a name from a submodule?

Leave a Comment