pythonweb-scrapingbeautifulsouplambda

Need an explanation for a web scraping lambda function in Python

I'm doing Web Scraping in Python and I've found this :

products = soup.find_all('li')
products_list = []
for product in products:
    name = product.h2.string
    price = product.find('p', string=lambda s: 'Price' in s).string
    products_list.append((name, price))

I'd like to understand the lambda function in this case, thank you so much.

Solution

  • You are creating a lambda (anonymous) function, which takes s as an argument and then checks if string "Price" is in the s or you can say if s contains string "Price". It will return True or False based on that.

    Also, you are storing that function inside string variable. So, you can call that lambda function by that variable: string(s).

    Here's an example (if it helps):

    
>>> # Create lambda function and store inside `string`
>>> string = lambda s: "Price" in s
>>> # Check `string` indeed a lambda function
>>> string
<function <lambda> at 0x7f4c0afa1630>
>>>
>>> # Call the lambda function with an argument
>>> # Inside lambda function, now, `s = "Hello, World"` !
>>> # It will check this: `"Price" in s`, it's not:
>>> string("Hello, World")
False
>>> # Now, `s = "What is the price of milk?"`
>>> # "Price" and "price" are not same !
>>> string("What is the price of milk?")
False
>>> string("Price of milk is $69.")
True

    This lambda function is same as this:

    def string(s):
    return "Price" in s