Python Multithreading Example

Summary: in this tutorial, you’ll learn how to use the Python threading module to develop a multithreaded program.

Inheriting from the Thread class

We’ll develop a multithreaded program that scraps the stock prices from the Yahoo Finance website.

To do that, we’ll use two third-party packages:

requests – to get the contents of a webpage.
lxml – to select a specific element of an HTML document.

First, install the requests and lxml modules using the pip command:

pip install request lxml

Code language: Python (python)

Next, define a new class called Stock that inherits from the Thread class of the threading module. We’ll place the Stock class in stock.py module:

import threading

class Stock(threading.Thread):
pass

Code language: Python (python)

Then, implement the __init__() method that accepts a symbol and initializes the url instance variable based on the symbol:

import threading
 import requests
 from lxml import html

class Stock(threading.Thread):
def __init__(self, symbol: str) -> None:
super().__init__()

self.symbol = symbol
self.url = f’https://finance.yahoo.com/quote/{symbol}‘
self.price = None

Code language: Python (python)

For example, if you pass the symbol GOOG to the __init__() method, the URL will be:

https://finance.yahoo.com/quote/GOOG

Code language: Python (python)

After that, override the run() method of the Thread class. The run() method gets the contents from the self.url and grabs the stock price:

import threading
 import requests
 from lxml import html

class Stock(threading.Thread):
def __init__(self, symbol: str) -> None:
super().__init__()

self.symbol = symbol
self.url = f’https://finance.yahoo.com/quote/{symbol}‘
self.price = None

def run(self):
response = requests.get(self.url)
if response.status_code == 200:
# parse the HTML
tree = html.fromstring(response.text)
# get the price in text
price_text = tree.xpath(
‘//*[@id=”quote-header-info”]/div[3]/div[1]/div[1]/fin-streamer[1]/text()’)
if price_text:
try:
self.price = float(price_text[0].replace(‘,’, ”))
except ValueError:
self.price = None

Code language: Python (python)

How it works.

Make a request to the URL using the requests.get() method:

response = requests.get(self.url)

Code language: Python (python)

If the request is successful, the HTTP status code is 200. In this case, we get the HTML contents from the response and pass it to the fromstring() function of the html module from the lxml package:

if response.status_code == 200:
 tree = html.fromstring(response.text)

Code language: Python (python)

Every element on a webpage can be selected using something called XPath.

To get the XPath of an element using Google Chrome, you inspect the page, right-click the element, select copy, and Copy XPath.

The XPath of the stock price at the time of writing this tutorial is as follows:

//*[@id="quote-header-info"]/div[3]/div[1]/div[1]/fin-streamer[1]

Code language: Python (python)

To get the text of the element, you append the text() at the end of the XPath:

//*[@id="quote-header-info"]/div[3]/div[1]/div[1]/fin-streamer[1]/text()

Code language: Python (python)

Notice that if Yahoo changes the page structure, you need to change the XPath accordingly. Otherwise, the program won’t work as expected:

price_text = tree.xpath('//*[@id="quote-header-info"]/div[3]/div[1]/div[1]/fin-streamer[1]/text()')

Code language: Python (python)

Once getting the price as text, we remove the comma and convert it to a number:

if price_text:
 try:
 self.price = float(price_text[0].replace(',', ''))
 except ValueError:
 self.price = None

Code language: Python (python)

Finally, add the __str__() method that returns the string representation of the Stock object:

import threading
 import requests
 from lxml import html

class Stock(threading.Thread):
def __init__(self, symbol: str) -> None:
super().__init__()

self.symbol = symbol
self.url = f’https://finance.yahoo.com/quote/{symbol}‘
self.price = None

def __str__(self):
return f’{self.symbol}\t{self.price}‘

Code language: Python (python)

Using the Stock class

The following main.py module uses the Stock class from the stock.py module:

from stock import Stock

symbols = [‘MSFT’, ‘GOOGL’, ‘AAPL’, ‘META’]
threads = []

for symbol in symbols:
t = Stock(symbol)
t.start()
threads.append(t)

for t in threads:
t.join()
print(t)

Code language: Python (python)

Output:

MSFT 253.67
 GOOGL 2280.41
 AAPL 145.86
 META 163.27

Code language: Python (python)

How it works.

First, import the Stock class from the stock.py module:

from stock import Stock

Code language: Python (python)

Second, initialize a list of symbols:

symbols = ['MSFT', 'GOOGL', 'AAPL', 'META']

Code language: Python (python)

Third, create a thread for each symbol, start it, and append the thread to the threads list:

threads = []
 for symbol in symbols:
 t = Stock(symbol)
 t.start()
 threads.append(t)

Code language: Python (python)

Finally, wait for all the threads in the threads list to complete and print out the stock price:

for t in threads:
 t.join()
 print(t)

Code language: Python (python)

Summary

Define a class that inherits from the threading.Thread class and override the run() method.

Python Multithreading Example

Python Multithreading Example

Inheriting from the Thread class

Using the Stock class

Summary

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Getting Started with Python Programming

Python Fundamentals

Control Flow

Functions

Python List

Python Dictionary

Python Set

Exception Handling

Python Loop with Else Clause

More on Functions

Modules

File I/O

Directory

Strings

Classes and objects

Section 2. Special methods

Section 3. Property

Section 4. Single inheritance

Section 5. Enumeration

Section 6. SOLID principles

Section 7. Multiple inheritances

Section 8. Descriptors

Section 9. Metaprogramming

Section 10. Exceptions