为何运行Python代码时未显示DeprecationWarning弃用警告信息

Hey there! I totally get why this is confusing—you’ve set up the warning call correctly, but it’s nowhere to be seen. Let’s break down what’s going on and fix it.

The Root Cause #

Python suppresses DeprecationWarning messages by default. These warnings are designed for library developers to spot outdated code, so the default warning filter hides them to avoid cluttering end-users’ output. That’s why you only see your print statement, but no warning text.

Fixes to Make the Warning Visible #

You’ve got a few straightforward ways to enable the warning:

1. Enable Warnings via Command Line #

When running your script, add the -W default flag to tell Python to show default warnings (including DeprecationWarning):

python -W default your_script_name.py

2. Modify the Warning Filter in Your Code #

Add a line right after importing warnings to explicitly enable DeprecationWarning for your script:

import warnings
# Turn on DeprecationWarning display
warnings.filterwarnings("default", category=DeprecationWarning)

def deprecate_something(arg1):
    arguments_by_list = do_something(arg1)
    print("Running deprecation check on arg1")
    warnings.warn(
        f"""
        arg1 attribute is deprecated. use {arguments_by_list}
        """,
        DeprecationWarning,
    )
    return arg1

# Example do_something function (since it wasn't defined in your original code)
def do_something(arg):
    return f"new_arg={arg}"

deprecate_something("HelloWorld")

This ensures the warning shows up every time the script runs.

3. Use warnings.simplefilter for a Global Toggle #

If you want to force all DeprecationWarnings to be displayed (not just this specific one), use simplefilter:

warnings.simplefilter('always', DeprecationWarning)

This overrides the default filter and makes every warning in the DeprecationWarning category visible.

What You’ll See After Fixing #

Once you apply any of these changes, your output should look like this:

Running deprecation check on arg1
__main__.py:10: DeprecationWarning: 
        arg1 attribute is deprecated. use new_arg=HelloWorld
        
  warnings.warn(

内容的提问来源于stack exchange，提问作者sony