The file inexplicably becomes very large after merging in python

Question

As shown in the figure, there are two csv files annotation and unigene, which have a common column name of "target gene accession". The annotation has 17071 lines and the unigene has 16868 lines, but the merged file has as many as 2344530 lines. May I ask why this is like this? Thank you :D!

Answer 1

你merge没加上联接字段
用法参考：http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.merge.html