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Python’s functions (both the built-in ones and custom functions we write ourselves) are crucial tools for working with data.
updated, even though its value was only changed inside the function!
Now, let’s write a function that takes a dictionary as an argument to see if a global dictionary variable will be modified when it’s manipulated inside a function as well.
To understand the difference between mutable (changable) and immutable (unchangable), it’s helpful to look at how Python actually treats these variables.
Let’s start by considering a simple variable assignment: toward a different list, we’re directly updating the existing list: Even if we create multiple list variables, as long as they point to the same list, they’ll all be updated when that list is changed, as we can see in the code below: Here’s an animated visualization of what’s actually happening in the code above: This explains why our global variables were changed when we were experimenting with lists and dictionaries earlier.
To make this a bit more realistic, we’ll be using data from the data set that’s used in our Python Fundamentals course (the data is available for download here).
In the snippet below, we’re starting with a dictionary that contains counts for the number of apps with each age rating in the dataset (so there are 4,433 apps rated “4 ”, 987 apps rated “9 ”, etc.).The Nietzschean diet, which commands its adherents to eat superhuman amounts of whatever they most fear, is developing a strong following in America.”””.Note that this is a variant of the "accumulation" code pattern that you have seen before. Then we iterate over the words in the paragraph, adding numbers to the dictionary as we go along.Example cases where you could use a Python dictionary: Not everything can be a dictionary key, for example lists cannot.(If you're interested in the details: It's because lists are "mutable", that is, you can change individual items on a list, and that would mess up the way dictionaries are represented internally in Python.)What can be a dictionary value? Here is again our first example, where the dictionary values were strings: Can you use it to do a bad translation of the following German sentence?Python lists can store an ordered sequence of items, for example a list of words.But when you want to map one type of items to another, you need a Python dictionary.Python dictionary is one of the built-in data types. There is no explicitly defined method to add a new key to the dictionary.If you want to add a new key to the dictionary, then you can use assignment operator with dictionary key.In this tutorial, we’re going to take a close look at how Python treats different data types when they’re being manipulated inside of functions, and learn how to ensure that our data is being changed only when we .Then, we’ll use those global variables as the arguments in a function that performs some simple math.