Table of Contents

• Absolute import vs implicit, explicit relative import
• Import in function
• Submodules related from
• Sorting imports
• Get a reference to the current module

Absolute import vs implicit, explicit relative import discussion

• from __future__ import absolute_import for py2
• Default in py3

foo
  |--__init__.py
  |--bar.py
  |--baz.py
bar.py
baz.py

• In implicit relative import, which is legacy and not recommended, the semantic of import bar is different among where it used.
  • In baz.py it will imports bar.py,
  • In foo/baz.py it will imports foo/bar.py

This would cause subtle bugs. At this point, we need absolute_import

from __future__ import absolute_import
import bar

With this code, import bar always imports bar.py, not things like foo/bar.py. To import foo/bar.py, there are two ways. One is absoulte import and the other is explicit relative import.

from __future__ import absolute_import

# Absolute import
import foo.bar

# Explicit relative import
# This is valid only when this file is in 'foo' package
# This way is discouraged; PEP8 prefers absolute imports
import .bar

Import in function discussion

• import will cache the module. So import in function won't cause reload and severe overhead.
• But import in function would still have addtional overhead for checking and resolving the cache, etc.
• So, use import in function only for optional library support or resolving circular dependency problem.
• import statement is just loading a module and giving a name for it. So we can perform a module level import within a function:

def foo():
    global math
    import math

Submodules related from

from package import item

1. Tests whether the item is defined in the package;
2. If not, it assumes it is a module and attempts to load it.
3. If it fails to find it, an ImportError exception is raised.

import item.subitem.subsubitem

1. Each item except for the last must be a package
2. The last item can be a module or a package but can’t be a class or function or variable defined in the previous item.

Sorting imports

Get a reference to the current module howto

import sys
current_module = sys.modules[__name__]