The any(iterable) function

This function returns True if at least one of the iterable's values is True. It is equivalent to

def any(iterable):
    for element in iterable:
        if element:
            return True
    return False

• when you need to search for a True value, and you don't know the number of values ahead of time

Imagine I own a business and I want to know which customers owe me money.

1. iterate over all customers
2. iterate over invoices for each customer
3. check each invoice for a balance due

Assume I have these classes and methods

class Customer:
    def invoices(self):
        ''' get all a customer's invoices '''

class Invoice:
    def balance_due(self):
        ''' get the unpaid balance '''

I can code

customers_owing_money = [
    customer 
    for customer in customers
    if any(
        invoice.balance_due() > 0 
        for invoice in customer.invoices()
    )
]

I now have a list of customers with unpaid balances.

However, couldn't I write this instead?

customers_owing_money = [
    customer 
    for customer in customers
        for invoice in customer.invoices()
            if invoice.balance_due() > 0
]

No, because this might produce duplicate customers in the final output. The any function avoids this problem by summarizing all the unpaid balances into a single True/False result.

See Stack Overflow: How exactly does the python any() function work?