assignment instance like df1.col1 = df2.col2 didn't work while using df[col1] = df[col2] worked

[PaperStrange]

Describe the bug A failure try to use another assignment instance

To Reproduce Steps to reproduce the behavior:

1. Go to 'middle process' -> 'expand training and testing data' -> 'combine all in one table' -> 'apply aggregation'
2. Find the 'aggregate_merchants' function
3. Replace 'df_agg["merchantid"] = df["merchant_id"]' by 'df_agg.merchantid = df.merchant_id'
4. Excude code below

Expected behavior A new column named by 'merchantid' will be assigned to df_agg

Screenshots None

Desktop

• OS: Ubuntu 14.0
• Browser chrome
• Version 71.0

Smartphone

• Device:
• OS:
• Browser
• Version

Additional context None

[PaperStrange]

This bug comes from the misunderstanding using of assignment of pandas dataframe