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Global variables are defined outside of any function. They can be accessed from any function within the same file. In the example code, X = 'Spam' is a global variable because it is defined outside the function func().

When the function tries to find the value of X, it looks in the local scope first. If X isn't found locally, it moves up to the global scope. That's why func() can access the value 'Spam' even though it is defined outside the function.

Defining a function in Python allows you to encapsulate code into reusable blocks. You use the def keyword followed by the function name and parentheses. Here’s how it looks:

def func():

Inside the curly braces, we place any operations we want the function to perform. In the given exercise, the function func() contains a single operation: print(X). When func is called, it prints the value of X.

Using functions helps keep your code organized and avoids repetition.

Variable scope determines where in the code a variable can be accessed. There are two main types of scope in Python: local and global.

Local scope refers to variables defined inside a function or block, accessible only within that function/block. Global scope refers to variables defined outside any function, and they can be accessed from anywhere in the code.

In the exercise, X is a global variable. It means the variable is accessible throughout the file, including inside func(). This is why the value 'Spam' could be accessed by the function.

Remember, if you define a variable inside a function with the same name as a global variable, the local variable will overshadow the global one within that function.

A function call is how you execute a function in Python. By using the function’s name followed by parentheses, you can run the code inside the function.

In the exercise, the line func() is a function call. When this line is executed, func goes through its code and performs any operations defined within it.

Upon calling func(), Python prints the value of X, which, as we know from the global scope, is 'Spam'. Function calls are essential for running code contained within functions and can be used as many times as needed.