python报错 name 'url' is not defined

url = 'https://api.blockchair.com/bitcoin/stats'

r = requests.get(url)
result = json.loads(r.text)
price=(result.get('context').get('market_price_usd'))

系统报错
r = requests.get(url)
NameError: name 'url' is not defined
请问怎么解决呢？

url = 'https://api.blockchair.com/bitcoin/stats'
是写在r = requests.get(url) 前面吗?
是不是url = 'https://api.blockchair.com/bitcoin/stats' 写在了if中没有执行到
把你的完整代码发一下看看
这样测试没有问题

import requests
import json

url = 'https://api.blockchair.com/bitcoin/stats'

r = requests.get(url)
result = json.loads(r.text)
print(result)

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import requests
import json
import datetime
import urllib.request
from lxml import html
import tkinter as tk

root = tk.Tk()
root.title("比特币实时价格 - 21C科技")
root.geometry("500x140")
root.iconbitmap("D:21c.ico")
root.config(bg="black")

frm = tk.Frame(root, bg="black")
frm.pack(pady=20)

logo = tk.PhotoImage(file="d:bitcoin.png")
cvs = tk.Canvas(frm, bg="black", width=100, height=100, highlightthickness=0)
cvs.grid(row=0, column=0, rowspan=2)
cvs.create_image(50, 50, image=logo)

lbl_bc = tk.Label(frm, text="Price", font=("Ds-Digital", 45), bg="black", fg="cyan", bd=0)
lbl_bc.grid(row=0, column=1, padx=20, sticky=tk.S)

lbl_time = tk.Label(frm, text="datetime", font=("Ds-Digital", 12), bg="black", fg="cyan", bd=0)
lbl_time.grid(row=1, column=1, sticky=tk.N)

def update():
URL = 'https://api.blockchair.com/bitcoin/stats'

r = requests.get(URL)
result = json.loads(r.text)
price=(result.get('context').get('market_price_usd'))
lbl_bc.config(text=f"$ {price}")
lbl_time.config(text=datetime.datetime.now().strftime("%Y-%m%d %H:%M:%S %p"))
root.after(1000, update)
update()
root.mainloop()

解决了吗？教教我怎么解决行吗