有没有办法循环通过 python 中的 function？

Question

I have this code which pulls data from the Federal Reserve, through their API. I am trying to figure out how to have different FRED ID's that can plug into the function and then output to a data table. So, for example, I would input "CPIAUCSL" and then it would give me a list of values, then the script would input "A191RL1Q225SBEA" and then append those values to the bottom of the data table (so that the values of CPIAUCSL would be above it). I tried to do this with the below script, but it would just overwrite the previous values. Any ideas?

import pandas as pd  
from requests import request  
import json  
from requests import request  
from urllib.request import urlopen  
from pandas import ExcelWriter  

def fred_variables(fred_id_list):  
    main_url= "https://api.stlouisfed.org/fred/series/observations?series_id="  
    API= "&api_key=50ebfb4929a3fe603e3b369d51826822"  
    file= "&file_type=json"  
    descending= "&sort_order=desc"  
    max_return= "&limit=21"  
    final_URL= main_url + fred_id_list + API + file + descending + max_return
    page = urlopen(final_URL)  
    data1= page.read()  
    nested_json = json.loads(data1)  
    json_file = pd.DataFrame.from_dict(pd.json_normalize(nested_json, record_path="observations"))  
    df= json_file  
    df['fredID'] = str(fred_id_list)  
    df2 = df.drop(df.columns[[0, 1]], axis=1)  
    return df2  

    fred_id_list=["CPIAUCSL","A191RL1Q225SBEA"]  
    for x in fred_id_list:  
        print(x)  

fred_variables(x)  
```[enter image description here][1]


  [1]: https://i.stack.imgur.com/8Tglt.png

Answer 1

I created a fake scenario for you:

data = {
    'CPIAUCSL': [12, 23, 1, 43, 12, 53, 13, 53, 1, 53, 123, 534],
    'A191RL1Q225SBEA': [65, 87, 23, 7, 23, 765, 23]
}

def fred_variables(fred_id):
    # processing code
    fake_result = data[fred_id]
    return fake_result

Consider the function is your function. I'm assuming you return a list of items. You can utilize Python's map function for your use-case. Like:

fred_id_list = ["CPIAUCSL","A191RL1Q225SBEA"]
result = list(map(fred_variables, fred_id_list))
print(result)

It will generate following output:

[[12, 23, 1, 43, 12, 53, 13, 53, 1, 53, 123, 534], [65, 87, 23, 7, 23, 765, 23]]

If you with the combine this whole data into one list, u can do the following:

final_result = []
for res in result:
    final_result.extend(res)

print(final_result)

The final output will be like:

[12, 23, 1, 43, 12, 53, 13, 53, 1, 53, 123, 534, 65, 87, 23, 7, 23, 765, 23]

For you specific case

Now coming to your question, you are returning a Pandas DataFrame from your function. So, what you need to do:

fred_id_list = ["CPIAUCSL","A191RL1Q225SBEA"]
result = list(map(fred_variables, fred_id_list))

Here result will be a list of DataFrames. You can combine all these DataFrames with the help of Pandas' concat function.

final_result = pd.concat(result)

I hope it helps. Thanks.