从 python 函数中返回 DataFrame 而不是使用 Pandas 的 pd.read_sql_query 列表

Question

I am struggling to understand why this returns a list containing a DataFrame rather than only the DataFrame. Is there something wrong with the code or a way to return only the DataFrame? It works as expected if not placed within a function.

import sqlite3
import pandas as pd

def get_tbl_info(db ='MyDatabase', table ='Measurements'):

        database = "/Users/Mary/Documents/Database/{DB}.db"..format(DB=db)

        conn = sqlite3.connect(database)

        tbl_info_command = "PRAGMA TABLE_INFO({table});".format(table=table)
        result_all = pd.read_sql_query(tbl_info_command,conn)
        print(type(result_all))
        return [result_all]



out = get_tbl_info()
print(type(out))

gives:

<class 'pandas.core.frame.DataFrame'>
<class 'list'>

Answer 1

Because when you enclose a variable with brackets [ ] , Python understands it as "ok put this variable inside a list" . Just replace the return of your function with:

return result_all

This should work properly, or actually your function could just return your dataframe directly

return pd.read_sql_query(tbl_info_command,conn)