Any and all

By now, you certainly know that Python has a lot of different built-in functions that help developers work more efficiently. Built-in functions are always available, so you don't need to declare or import them. Just call such a function whenever you need it. You have already seen one of those functions, it is print(). Today we will learn two more built-in functions any() and all() and find out how and when to use them.

Be careful though, these functions work only with iterable objects, e.g. strings and lists. A list is iterable, so we will use it to illustrate the theoretical part and to show how any() and all() work.

Function any()

The result of the any() function call is the boolean value: it returns True if an element or a group of elements in an iterable object are evaluated True. Otherwise, it returns False. Let’s take a look at the example. Imagine that you and your friends, Jam and Andy, wrote a test and got your results in the form of a list with True and False values. The test is passed if at least one answer is correct. Now you need to check if you and your friends passed that test.

your_results = [True, False, False]
print(any(your_results))  # True

As you know, the value True corresponds to 1, while False can be represented by 0, therefore, you can replace the boolean values with the numerical ones in the list above and get the same result.

your_results = [1, 0, 0]
print(any(your_results))  # True

In fact, all numbers other than 0 will be regarded as True, even the negative ones. That part stems from how the bool() function works.

Now back to our test example, you passed with one correct answer. What about your friends, Jam and Andy? Andy has a different list of results to check.

andy_results = [False, False, False]
print(any(andy_results))  # False

Unfortunately, your friend Andy failed. What about Jam? Well, this friend of yours didn't write the test at all, so he got an empty list of results.

jam_results = []
print(any(jam_results))  # False

The list doesn't contain any elements, and since no True value is to be found the any() function returns False.

So what does the any() function do? First, it takes a list as an argument, then evaluates all the elements of this list to find at least one True, if so, it returns True, otherwise, the result is False.

Function all()

The all() function works pretty much like any(). The difference is that all() function checks if all the elements of an iterable object are True and returns True if they are. Otherwise, you get False. Do you remember the story from the previous section where we checked the results of the test? Let's proceed. Imagine yet another test, this time the final one. To succeed, you should answer all the questions correctly. How did it go this time for you and the two friends of yours?

your_results = [True, False, False]
print(all(your_results))  # False

As you can see, not all the answers in your case are correct, so you didn't pass the test. What about Andy's results?

andy_results = [True, True, True]
print(all(andy_results))  # True

Luckily, Andy passed. Jam seems to have a vacation. His list of results is empty again.

jam_results = []
print(all(jam_results))  # True

The list doesn't contain any elements, but the all() function will return True because it searches for any False values. No False values result in True. Be careful with this scenario.

Non-boolean values

Pay attention to the fact that any() and all() can take a list containing non-boolean values. Let's recall how they are evaluated.

Empty sequences, e.g. strings and lists, as well as zero, are equivalent to False, the same applies to the constant None. Non-empty sequences are equivalent to True.

Here is a list with false values. any() and all() will have the same behavior in this example:

rocket_science_scores = [0, -0, 0.0, +0]
any(rocket_science_scores)  # False
all(rocket_science_scores)  # False

Now, let's look at the scores of some simpler subject:

math_scores = [0, 1, 2, 3]
any(math_scores)  # True
all(math_scores)  # False

As shown, all() doesn't return True for a list where false values are present. Consider the last case:

biology_scores = [1, 2, 3, 4]
any(biology_scores)  # True
all(biology_scores)  # True

The list biology_scores has no false values, that's why both functions result in True.

Also, you can turn the elements of your list into the boolean values via comparison. Suppose, we have a list of scores and want to check whether some are equal to 3 or greater. It can be done like this:

scores = [1, 2, 3, 4]
boolean_scores = [score >= 3 for score in scores]  # [False, False, True, True]
print(any(boolean_scores))  # True
print(all(boolean_scores))  # False

However, lists may contain different elements, e.g. strings or nested lists, in such cases, the behavior of any() and all() would depend largely on the contents. Keep that in mind.

Conditions

Coders often use any() and all() functions in conditions. It helps to check the elements of iterable objects quickly and to avoid complex constructions.

Let's choose a candy box for Valentine's Day. Each box contains several types of sweets. But you are interested in the even amount of candies of each type because, obviously, you will share them with your valentine.

box = [10, 20, 33]

if any([candy % 2 for candy in box]):
    print("It is not a proper gift.")
else:
    print("Perfect!")

Short and sweet, isn't it? Life is like a box of chocolates! As long as the values you deal with can be converted to True and False, it's safe to use both functions in conditions.

Summary

We learned what any() and all() functions can do and how they work. As you can see, these functions are an efficient tool that helps check conditions and may improve the readability of your code.