Python 3.8 Tutorials

Strings | Core Python 3.8

Strings Now what was all that "Hello, " + name + "!" stuff about? The first program in this chapter was simply print("Hello, world!") It is customary to begin with a program like this in programming tutorials. The problem is that I haven’t really explained how it works yet. You know the basics of the print statement (I’ll have more to say about that later), but what is "Hello, world!"? It’s called a string (as in “a string of characters”). Strings are found in almost every useful, real-world Python program and have many uses. Their main use is to represent bits of text, such as the exclamation “Hello, world!” Single-Quoted Strings and Escaping Quotes Strings are values, just as numbers are: >>> "Hello, world!" 'Hello, world!' There is one thing that may be a bit surprising about this example, though: when Python printed out our string, it used single quotes, whereas we used double quotes. What’s the differ...

Variables and Statements | Core Python 3.8

Variables Another concept that might be familiar to you is variables. If algebra is but a distant memory, don’t worry: variables in Python are easy to understand. A variable is a name that represents (or refers to) some value. For example, you might want the name x to represent 3. To make it so, simply execute the following: >>> x = 3 This is called an assignment. We assign the value 3 to the variable x. Another way of putting this is to say that we bind the variable x to the value (or object) 3. After you’ve assigned a value to a variable, you can use the variable in expressions. >>> x * 2 6 Unlike some other languages, you can’t use a variable before you bind it to something. There is no “default value.” ■ Note the simple story is that names, or identifiers, in python consist of letters, digits, and underscore characters (_). they can’t begin with a digit, so Plan9 is a valid variable name, whereas Plan is not. Statements Until...

Execution the Program | Core Python 3.8

Saving and Executing Your Programs The interactive interpreter is one of Python’s great strengths. It makes it possible to test solutions and to experiment with the language in real time. If you want to know how something works, just try it! However, everything you write in the interactive interpreter is lost when you quit. What you really want to do is write programs that both you and other people can run. In this section, you learn how to do just that. First of all, you need a text editor, preferably one intended for programming. (If you use something like Microsoft Word, which I really don’t really recommend, be sure to save your code as plain text.) If you are already using IDLE, you’re in luck. With IDLE, you can simply create a new editor window with File › New File. Another window appears, without an interactive prompt. Whew! Start by entering the following: print("Hello, world!") Now select File › Save to save your program (which is, in fact, a pl...

Dictionaries: When Indices Won’t Do | Core Python 3.8

You’ve seen that lists are useful when you want to group values into a structure and refer to each value by number. In this chapter, you learn about a data structure in which you can refer to each value by name. This type of structure is called a mapping. The only built-in mapping type in Python is the dictionary. The values in a dictionary don’t have any particular order but are stored under a key, which may be a number, a string, or even a tuple. Dictionary Uses The name dictionary should give you a clue about the purpose of this structure. An ordinary book is made for reading from start to finish. If you like, you can quickly open it to any given page. This is a bit like a Python list. On the other hand, dictionaries—both real ones and their Python equivalent—are constructed so that you can look up a specific word (key) easily to find its definition (value). A dictionary is more appropriate than a list in many situations. Here are some examples of uses of Pyth...

Lists and Tuples | Core Python 3.8

This chapter introduces a new concept: data structures. A data structure is a collection of data elements (such as numbers or characters, or even other data structures) that is structured in some way, such as by numbering the elements. The most basic data structure in Python is the sequence. Each element of a sequence is assigned a number—its position, or index. The first index is zero, the second index is one, and so forth. Some programming languages number their sequence elements starting with one, but the zeroindexing convention has a natural interpretation of an offset from the beginning of the sequence, with negative indexes wrapping around to the end. If you find the numbering a bit odd, I can assure you that you’ll most likely get used to it pretty fast. This chapter begins with an overview of sequences and then covers some operations that are common to all sequences, including lists and tuples. These operations will also work with strings, which will be use...

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