What is a Circular Import Error?

A circular import occurs when module A imports from module B, and module B also imports from module A. When Python first loads A, it starts loading B, which tries to import from A before A has finished initializing, resulting in an ImportError or partially initialized module.

Why it happens

• •Two modules that depend on each other import each other at the module level.
• •A utilities module imports from a models module that imports from utilities.
• •Shared constants or helpers placed in a module that also imports domain logic.
• •Frameworks with plugin systems where plugins import from the core and the core imports plugins.

Examples

# a.py
from b import greet

def name():
    return "Alice"

# b.py
from a import name

def greet():
    return f"Hello {name()}"

ImportError: cannot import name 'greet' from partially initialized module 'b' (most likely due to a circular import)

# a.py - no import from b at top level
def name():
    return "Alice"

# b.py
def greet():
    from a import name  # local import breaks the cycle
    return f"Hello {name()}"

Related errors

• ImportError
• ModuleNotFoundError
• RuntimeError