A NameError typically occurs when Python cannot find the variable you referenced.

When sorting a pandas DataFrame, this often happens if the column name is written without quotes, making Python treat it as a variable instead of a string.

Example that causes the error:

df.sort_values(by=column_name)

If column_name is not defined, Python raises a NameError.

The correct approach is:

df.sort_values(by="column_name")

Also make sure the column actually exists in the DataFrame. You can verify this with:

print(df.columns)