for循环仅打印实时市场中dict的最后一个值

Question

try to print LTP data for more than one crypto in live market but printing only for one crypto.

import pandas as pd
import requests
import json

ltp_data= []

crypto = {"BTCUSDT",  "LTCUSDT", "DOGEUSDT"}
def live_ltp():
    for i in crypto:
        key = "https://api.binance.com/api/v3/ticker/price?symbol="
        url = key+i
        response = requests.get(url)
        Ltp = response.json()
        ltp_data.append(Ltp)
        return Ltp
while True:
    print(str(live_ltp())) 

Answer 1

return will exit your loop as soon as it is hit. If you bring your return statement outside of the loop, and have it return ltp_data (instead of the "LTP" json object) you should be able to get the items in the list you appear to be populating.

ltp_data= []

crypto = {"BTCUSDT",  "LTCUSDT", "DOGEUSDT"}
def live_ltp():
    for i in crypto:
        key = "https://api.binance.com/api/v3/ticker/price?symbol="
        url = key+i
        response = requests.get(url)
        Ltp = response.json()
        ltp_data.append(Ltp)
    return ltp_data

crypto_ltps = live_ltp()
print(crypto_ltps)

Answer 2

You have a return Ltp in the for loop so you will always just get a single response for the first item in the set of crypto id's. You could instead do return lpd_data after the loop ends. But that creates a new problem - since you are updating a global list, it will just keep growing and growing.

Instead, write your function to take input parameters and return a locally-generated list.

import pandas as pd
import requests
import json

def live_ltp(crypto_ids):
    ltp_data = []
    for i in crypto_ids:
        key = "https://api.binance.com/api/v3/ticker/price?symbol="
        url = key+i
        response = requests.get(url)
        Ltp = response.json()
        ltp_data.append(Ltp)
    return ltp_data

crypto = {"BTCUSDT",  "LTCUSDT", "DOGEUSDT"}

while True:
    print(str(live_ltp(crypto))) 

Answer 3

You have added the return statement at the end of loop because of which it's executing only one time and returning only 1 data.

Instead,

import pandas as pd
import requests
import json

ltp_data= []

crypto = {"BTCUSDT",  "LTCUSDT", "DOGEUSDT"}
def live_ltp():
    responses = []
    for i in crypto:
        key = "https://api.binance.com/api/v3/ticker/price?symbol="
        url = key+i
        response = requests.get(url)
        Ltp = response.json()
        ltp_data.append(Ltp)
        responses.append(Ltp)
    return responses
while True:
    print(str(live_ltp()))

This will solve the problem.
Hope this helps you.!! Please free to comment if you get any error in this and mark the answer as correct if it worked.

Answer 4

solution with dataframe in place.

you will need to pass empty dataframe to function: live_ltp(df_frame) .

I would also use .json_normalize to set table in place properly.

import pandas as pd
import requests
import json


ltp_data = pd.DataFrame() # empty dataframe (not list) which will be updated in the function below
crypto = {"BTCUSDT",  "LTCUSDT", "DOGEUSDT"}

def live_ltp(df_frame):
    for i in crypto:
        key = "https://api.binance.com/api/v3/ticker/price?symbol="
        url = key+i
        response = requests.get(url)
        Ltp = response.json()
        ltp_df = pd.json_normalize(Ltp)
        ltp_df['time'] = pd.Timestamp.now()
        df_frame = pd.concat([df_frame, ltp_df], axis=0)
    return df_frame


while True:
    final_df = live_ltp(ltp_data) # passing empty dataframe to function
    final_df.to_excel('test.xlsx', index=False)
    print(final_df)