Welcome @Quent to our community! I’m Jay and I am a n8n verified creator.
In n8n’s Python Code node, the variable is items (not _input). Each item in items is a dict with a json key. Here’s the corrected version:
for item in items:
row = item["json"]
for column_name, value in row.items():
print(f"Column: {column_name}")
print(f"Value: {value}")
return items
Note: you also need to return items at the end of the Code node or it will return nothing downstream.