熊猫数据框未附加

Question

我正在尝试通过for循环追加数据帧。

代码

def redshift_to_pandas(sql_query,**kwargs):
# pass a sql query and return a pandas dataframe
 cur.execute(sql_query)
 columns_list = [desc[0] for desc in cur.description]
 data = pd.DataFrame(cur.fetchall(),columns=columns_list)
 return data

输入- all_schema = [('backup')]

循环-

try:
 if len(all_schema) == 0:
  raise inputError("The Input has no schema selected. EXITING")
 else:
  modified_schemadf=pd.DataFrame(columns=['columns_name','status'])
  
  for i in range(len(all_schema)):
    #print (redshift_to_pandas("select '"+all_schema[i]+"' as columns_name,(select exists ( select distinct table_schema from information_schema.tables where table_schema like '%"+all_schema[i]+"')) as status",mechanism='append'))
    modified_schemadf.append(redshift_to_pandas("select '"+all_schema[i]+"' as columns_name,(select exists ( select distinct table_schema from information_schema.tables where table_schema like '%"+all_schema[i]+"')) as status",mechanism='append'))
    print (modified_schemadf)

except inputError as e:
   print(e.message)
   logger.error("UNEXPECTED INPUT FOUND, Please check the I/P List . EXITING")
  
print (modified_schemadf)

我觉得这个问题很明显，但是我似乎没有找到问题。

这里是o / p-

因此，第一个打印件（已注释掉）确实向我返回了正确的结果。 接下来的步骤，即将结果附加到声明的数据帧（名称-Modifyed_schemadf）是问题区域。当我打印其值时，它仍然抛出一个空的数据框。由于某种原因，附加操作没有发生。

当代码输入 else 时，即当输入合法时，将创建一个空的数据框，称为Modify_schemadf。对于这个空的数据框，附加项的数量将与输入项的数量一样。

预先感谢。

请不要介意缩进，复制可能会影响缩进。

Answer 1

问题不只是您没有分配附加的数据框吗？尝试更改此行

modified_schemadf.append(redshift_to_pandas("select '"+all_schema[i]+"' as columns_name,(select exists ( select distinct table_schema from information_schema.tables where table_schema like '%"+all_schema[i]+"')) as status",mechanism='append'))

此行

modified_schemadf = modified_schemadf.append(redshift_to_pandas("select '"+all_schema[i]+"' as columns_name,(select exists ( select distinct table_schema from information_schema.tables where table_schema like '%"+all_schema[i]+"')) as status",mechanism='append'))