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In Python, wrappers are modifications to functions or classes which change the behavior in some way. They are called wrappers because they “wrap” around the existing code to modify it. This is most commonly used with function wrapping, but we can also wrap classes. Let’s take a look at an example of a class wrapper:

First, we need a class to wrap around.

class Customer: def __init__(self, name, age, address, phone_number): self.name = name self.age = age self.address = address self.phone_number = phone_number

Next, we create a wrapper class which stores an object of the class we are wrapping around. It also includes some additional functionality.

class CustomerWrap(Customer): def __init__(self, name, age, address, phone_number): self.customer = Customer(name, age, address, phone_number) def display_customer_info(self): print('Name: ' + self.customer.name) print('Age: ' + str(self.customer.age)) print('Address: ' + self.customer.address) print('Phone Number: ' + self.customer.phone_number)

Finally, we can create an object from the wrapper class to access the new functionality and the wrapped class contained inside.

customer = CustomerWrap('Dmitri Buyer', 38, '123 Python Avenue', '5557098603') customer.display_customer_info() # Output # Name: Dmitri Buyer # Age: 38 # Address: 123 Python Avenue # Phone Number: 5557098603

Wrapper classes allow us to create different variations of classes with different purposes while avoiding duplicate code. Since we use an instance of the wrapped class inside of it, it preserves all of the attributes and methods from the wrapped class and keeps us from having to re-type all of the code.

In the case of containers, the collections class has three different wrapper classes set up for us to modify! Because of this, we can refer to them as wrapper containers. The advanced containers which we have already been looking at are variations of the standard built-in containers, so using wrapper containers allows us to create our own versions as well.

The three wrapper containers we will be looking at are:

  • UserDict
  • UserList
  • UserString

Instructions

Take a look at the provided CustomerWrap class. Play around with the code and then click Next to move on!

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