Python3.5中importlib.import_module相对模块名导入异常问题咨询

Let's break down why you're seeing import failures with relative module names in Python 3.5, and how to fix it.

Common Causes of the Failure #

When using a relative module name (starting with .) with importlib.import_module, two critical rules must be followed in Python 3.5:

• The pkgname argument must be the full, exact name of an already-imported package that exists in sys.modules.
• Truncated or incorrect package names (like your example's "tes...") will break the relative path resolution entirely.
• Python 3.5 has stricter handling of relative imports compared to later versions—if the target package isn't already loaded into the interpreter, importlib can't resolve the relative path.

Step-by-Step Fix #

First, let's align your test code with these rules. Here's the corrected version of test_impl.py:

import importlib
import sys
import test0  # Ensure the target package is loaded into sys.modules first

print(sys.version_info)

def test_imp_module(module_name, pkgname):
    try:
        _m = importlib.import_module(module_name, pkgname)
        print("import OK: module={}, pkg={}".format(module_name, pkgname))
    except Exception as e:
        print(f"Import failed: {str(e)}")

# Use the full, correct package name "test0" for pkgname
test_imp_module(".test1", "test0")
test_imp_module(".test2", "test0")

Why This Works #

1. Pre-import the package: By adding import test0, we ensure the package is registered in sys.modules—this is required for Python 3.5 to resolve relative paths using importlib.import_module.
2. Correct pkgname: Using the full package name "test0" instead of a truncated string gives importlib a valid anchor point to locate the relative module (.test1/.test2).

Alternative: Import Without Pre-Loading the Package #

If you don't want to pre-import the package, you can use importlib.util to construct the module spec manually, but this is more verbose. For most cases, pre-importing the package is the simplest and most reliable approach in Python 3.5.

内容的提问来源于stack exchange，提问作者Wang