How many 3-letter codes can you make using the letters J e C K if each code must not repeat a letter
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Python’s is a built-in function that allows you to process and transform all the items in an iterable without using an explicit Show
In this tutorial, you’ll learn:
With this knowledge, you’ll be able to use For a better understanding of Free Bonus: 5 Thoughts On Python Mastery, a free course for Python developers that shows you the roadmap and the mindset you’ll need to take your Python skills to the next level. Coding With Functional Style in PythonIn functional programming, computations are done by combining functions that take arguments and return a concrete value (or values) as a result. These functions don’t modify their input arguments and don’t change the program’s state. They just provide the result of a given computation. These kinds of functions are commonly known as pure functions. In theory, programs that are built using a functional style will be easier to:
Functional programming typically uses lists, arrays, and other iterables to represent the data along with a set of functions that operate on that data and transform it. When it comes to processing data with a functional style, there are at least three commonly used techniques:
According to Guido van Rossum, Python is more strongly influenced by imperative programming languages than functional languages:
However, back in 1993, the Python community was demanding some functional programming features. They were asking for:
These functional features were added to the language thanks to the contribution of a community member. Nowadays, , , and In this tutorial, you’ll cover one of these functional features, the built-in function Getting Started With Python’s >>> str_nums = ["4", "8", "6", "5", "3", "2", "8", "9", "2", "5"] >>> int_nums = map(int, str_nums) >>> int_numsSometimes you might face situations in which you need to perform the same operation on all the items of an input iterable to build a new iterable. The quickest and most common approach to this problem is to use a Python In the following three sections, you’ll learn how Understanding >>> str_nums = ["4", "8", "6", "5", "3", "2", "8", "9", "2", "5"] >>> int_nums = map(int, str_nums) >>> int_numsAccording to the , Note: The first argument to This first argument to The operation that To better understand >>> When you run this loop on You can achieve the same result without using an explicit loop by using >>> Since A second advantage of using Note: In Python 2.x, returns a list. This behavior changed in . Now, For another example, say you need to convert all the items in a list from a string to an integer number. To do that, you can use >>> Using >>> str_nums = ["4", "8", "6", "5", "3", "2", "8", "9", "2", "5"] >>> int_nums = map(int, str_nums) >>> int_numsYou can use any kind of Python callable with There are some built-in functions that you can use with >>> You can use any built-in function with A common pattern that you’ll see when it comes to using >>> Processing Multiple Input Iterables With >>> str_nums = ["4", "8", "6", "5", "3", "2", "8", "9", "2", "5"] >>> int_nums = map(int, str_nums) >>> int_numsIf you supply multiple iterables to Consider the following example that uses : >>> This technique allows you to merge two or more iterables of numeric values using different kinds of math operations. Here are some examples that use >>> In the first example, you use a subtraction operation to merge two iterables of three items each. In the second example, you add together the values of three iterables. Transforming Iterables of Strings With Python’s >>> str_nums = ["4", "8", "6", "5", "3", "2", "8", "9", "2", "5"] >>> int_nums = map(int, str_nums) >>> int_numsWhen you’re working with iterables of string objects, you might be interested in transforming all the objects using some kind of transformation function. Python’s Using the Methods of >>> numbers = [1, 2, 3, 4, 5] >>> squared = [] >>> for num in numbers: ... squared.append(num ** 2) ... >>> squared [1, 4, 9, 16, 25] 42A quite common approach to is to use some of the to transform a given string into a new string. If you’re dealing with iterables of strings and need to apply the same transformation to each string, then you can use >>> There are a few transformations that you can perform on every item in You can also use some methods that take additional arguments with default values, such as , which takes an optional argument called >>> When you use Note: If you need to supply arguments rather than rely on the default value, then you can use a Here’s an example that uses >>> The This technique can be handy when, for example, you’re processing text files in which lines can have trailing spaces (or other characters) and you need to remove them. If this is the case, then you need to consider that using Removing PunctuationWhen it comes to processing text, you sometimes need to remove the punctuation marks that remain after you split the text into words. To deal with this problem, you can create a custom function that removes the punctuation marks from a single word using a regular expression that matches the most common punctuation marks. Here’s a possible implementation of this function using , which is a regular expression function that lives in the module in Python’s standard library: >>> Inside With your transformation function in place, you can use >>> In this piece of text, some words include punctuation marks. For example, you have Note that the apostrophe ( Implementing a Caesar Cipher AlgorithmJulius Caesar, the Roman statesman, used to protect the messages he sent to his generals by encrypting them using a cipher. A Caesar cipher shifts each letter by a number of letters. For example, if you shift the letter If the shift goes beyond the end of the alphabet, then you just need to rotate back to the beginning of the alphabet. In the case of a rotation by three,
The following code implements Inside >>> If you add this integer to the target number of If the new position of the letter doesn’t go beyond the position of the last letter ( >>> Finally, if the new rotated position is beyond the position of the last letter ( With >>> Strings are also iterables in Python. So, the call to Transforming Iterables of Numbers With Python’s >>> str_nums = ["4", "8", "6", "5", "3", "2", "8", "9", "2", "5"] >>> int_nums = map(int, str_nums) >>> int_numsIn the following sections, you’ll cover some examples of how to use Using Math OperationsA common example of using math operations to transform an iterable of numeric values is to use the . In the following example, you code a transformation function that takes a number and returns the number squared and cubed: >>> There are a lot of math-related transformations that you can perform with >>> In this case, you transform You can perform a wide spectrum of math transformations on an iterable of numbers using Converting TemperaturesAnother use case for You can code two transformation functions to accomplish this task: These functions will be your transformation functions. You can use them with >>> If you call To extend this example and cover any other kind of unit conversion, you just need to code an appropriate transformation function. Remove adsConverting Strings to NumbersWhen working with numeric data, you’ll likely deal with situations in which all your data are string values. To do any further calculation, you’ll need to convert the string values into numeric values. If you’re sure that your data is clean and doesn’t contain wrong values, then you can use or >>> In the first example, you use If you’re not sure that your data is clean, then you can use a more elaborate conversion function like the following: >>> Inside You can customize Combining >>> str_nums = ["4", "8", "6", "5", "3", "2", "8", "9", "2", "5"] >>> int_nums = map(int, str_nums) >>> int_numsSo far, you’ve covered how to use >>> str_nums = ["4", "8", "6", "5", "3", "2", "8", "9", "2", "5"] >>> int_nums = map(int, str_nums) >>> int_numsSometimes you need to process an input iterable and return another iterable that results from filtering out unwanted values in the input iterable. In that case, Python’s
To illustrate how you can use >>> With a negative number as an argument, >>> >>> str_nums = ["4", "8", "6", "5", "3", "2", "8", "9", "2", "5"] >>> int_nums = map(int, str_nums) >>> int_numsPython’s
Here’s an example that combines >>> In this example, you call to get the path to your home directory. Then you call on that path to get a list with the paths of all the files that live there. The call to Note: Some years ago, Google developed and started using a programming model that they called MapReduce. It was a new style of data processing designed to manage big data using parallel and distributed computing on a cluster. This model was inspired by the combination of the map and reduce operations commonly used in functional programming. The MapReduce model had a huge impact on Google’s ability to handle huge amounts of data in a reasonable time. However, by 2014 Google was no longer using MapReduce as their primary processing model. Nowadays, you can find some alternative implementations of MapReduce like Apache Hadoop, which is a collection of open source software utilities that use the MapReduce model. Even though you can use >>> This example is a lot more readable and efficient than the example that you saw before. If you want to dive deeper into how to use Processing Tuple-Based Iterables With >>> str_nums = ["4", "8", "6", "5", "3", "2", "8", "9", "2", "5"] >>> int_nums = map(int, str_nums) >>> int_numsPython’s The main difference between The says that the function is roughly equivalent to the following Python function: The >>> In the first example, you use to calculate the power of the first value raised to the second value in each tuple. The tuples will be in the form If every tuple in your iterable has two items, then If you use >>> Note that >>> In this case, you have two tuples instead of a list of tuples. You’ve also swapped Coding With Pythonic Style: Replacing >>> str_nums = ["4", "8", "6", "5", "3", "2", "8", "9", "2", "5"] >>> int_nums = map(int, str_nums) >>> int_numsFunctional programming tools like For example, the functionality provided by Using List ComprehensionsThere’s a general pattern that you can use to replace a call to Note that the list comprehension almost always reads more clearly than the call to Here’s an example of how to replace >>> If you compare both solutions, then you might say that the one that uses the list comprehension is more readable because it reads almost like plain English. Additionally, list comprehensions avoid the need to explicitly call Using Generator ExpressionsPython iterators are known to be quite efficient in terms of memory consumption. This is the reason why There’s a tiny syntactical difference between a list comprehension and a generator expression. The first uses a pair of square brackets ( You can use generator expressions to write code that reads clearer than code that uses >>> This code has a main difference from the code in the previous section: you change the square brackets to a pair of parentheses to turn the list comprehension into a generator expression. Generator expressions are commonly used as arguments in function calls. In this case, you don’t need to use parentheses to create the generator expression because the parentheses that you use to call the function also provide the syntax to build the generator. With this idea, you can get the same result as the above example by calling >>> If you use a generator expression as an argument in a function call, then you don’t need an extra pair of parentheses. The parentheses that you use to call the function provide the syntax to build the generator. Generator expressions are as efficient as ConclusionPython’s allows you to perform mapping operations on iterables. A mapping operation consists of applying a transformation function to the items in an iterable to generate a transformed iterable. In general, In this tutorial, you’ve learned how You now know how to:
With this new knowledge, you’ll be able to use Mark as Completed Watch Now This tutorial has a related video course created by the Real Python team. Watch it together with the written tutorial to deepen your understanding: Python's map() Function: Transforming Iterables 🐍 Python Tricks 💌 Get a short & sweet Python Trick delivered to your inbox every couple of days. No spam ever. Unsubscribe any time. Curated by the Real Python team.  Send Me Python Tricks » About Leodanis Pozo Ramos Leodanis is an industrial engineer who loves Python and software development. He's a self-taught Python developer with 6+ years of experience. He's an avid technical writer with a growing number of articles published on Real Python and other sites. » More about LeodanisEach tutorial at Real Python is created by a team of developers so that it meets our high quality standards. The team members who worked on this tutorial are: Aldren Bryan Geir Arne Joanna Jacob Master Real-World Python Skills With Unlimited Access to Real Python Join us and get access to thousands of tutorials, hands-on video courses, and a community of expert Pythonistas: Level Up Your Python Skills » Master Real-World Python Skills Join us and get access to thousands of tutorials, hands-on video courses, and a community of expert Pythonistas: Level Up Your Python Skills » What Do You Think? Rate this article: Tweet Share Share EmailWhat’s your #1 takeaway or favorite thing you learned? How are you going to put your newfound skills to use? Leave a comment below and let us know. Commenting Tips: The most useful comments are those written with the goal of learning from or helping out other students. and get answers to common questions in our support portal. How many 3There are 15,600 different 3-letter passwords, with no letters repeating, that can be made using the letters a through z.
How many 3Therefore number of possible codes =720. Was this answer helpful?
How many 3If repetition is allowed, we have 4 choices for each letter. Therefore, we can form 4*4*4 = 64 such “words". Good luck!
How many 3 alphabet arrangements are there with at least one repetition of arrangements )?If the letters are distinct and repetition is allowed then 4 * 4 * 4 = 4^3 = 64.
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