How Have Import Statements Changed in Python 3?

Changes in Import Statement in Python 3

In Python 3, the import mechanism has undergone significant revisions, introducing new rules for relative imports and restricting star imports.

What is a Relative Import?

A relative import is an import statement that refers to a module or package relative to the current module's location in the file system. For example, consider the following file structure:

mypkg/
  __init__.py
  module1.py
  module2.py

In module2.py, the statement from module1 import Foo would be a relative import, as it imports the Foo class from the sibling module module1.

Explicit Relative Imports

Python 3 requires explicit relative imports, which clearly specify the location of the imported module. The leading period (".") in an import statement indicates a relative import. For example, from .module1 import Foo imports Foo from the relative module module1.

Removal of Implicit Relative Imports

In Python 2, implicit relative imports allowed modules to be imported without explicitly specifying their location. However, this behavior has been deprecated in Python 3. For example, the statement import module1 in Python 2 would implicitly import module1.py from the current directory. However, in Python 3, this statement would raise an error, requiring an explicit import using from . import module1.

Star Imports

Star imports (e.g. from x import *) are only permitted in module-level code in Python 3. This means that modules cannot use star imports when importing other modules.

Example of Using Relative Imports

Consider the following Python 2 code:

# module1.py
class MyClass:
    def __init__(self):
        print("Hello from MyClass")

# module2.py
from module1 import MyClass

In Python 3, module2.py would have to be rewritten as:

# module2.py
from .module1 import MyClass

This explicit relative import ensures that MyClass is imported from the correct location relative to module2.

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