TypeError: static_folder must be a string

TypeError: static_folder must be a string

$ python -c "from flask import Flask; app=Flask(__name__, static_folder=123)"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
TypeError: static_folder must be a string

Why this happens

static_folder config expects a filesystem path as a string. Passing integers or other objects raises TypeError. This often happens when reading configuration from environment without converting types.

Fix

Provide a proper string path or None to disable static. Use absolute or relative paths as strings.

Wrong code

from flask import Flask

app = Flask(__name__, static_folder=123)

Fixed code

from flask import Flask

app = Flask(__name__, static_folder="static")

Additional notes

• Blueprints also accept static_folder string.
• Combine with static_url_path to customize URL.
• Ensure the folder exists to avoid 404 when serving static files.