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...

Files and Stuff | Core Python 3.8

So far, we’ve mainly been working with data structures that reside in the interpreter itself. What little interaction our programs have had with the outside world has been through input and print. In this chapter, we go one step further and let our programs catch a glimpse of a larger world: the world of files and streams. The functions and objects described in this chapter will enable you to store data between program invocations and to process data from other programs. Opening Files You can open files with the open function, which lives in the io module but is automatically imported for you. It takes a file name as its only mandatory argument and returns a file object. Assuming that you have a text file (created with your text editor, perhaps) called somefile.txt stored in the current directory, you can open it like this: >>> f = open('somefile.txt') You can also specify the full path to the file, if it’s located somewhere else. If it doesn’t exist, however, ...

Unicode, bytes, and bytearray | Core Python 3.8

Python strings represent text using a scheme known as Unicode. The way this works for most basic programs is pretty transparent, so if you’d like, you could skip this section for now and read up on the topic as needed. However, as string and text file handling is one of the main uses of Python code, it probably wouldn’t hurt to at least skim this section. Abstractly, each Unicode character is represented by a so-called code point, which is simply its number in the Unicode standard. This allows you to refer to more than 120,000 characters in 129 writing systems in a way that should be recognizable by any modern software. Of course, your keyboard won’t have hundreds of thousands of keys, so there are general mechanisms for specifying Unicode characters, either by 16- or 32-bit hexadecimal literals (prefixing them with \u or \U, respectively) or by their Unicode name (using \N{name}). >>> "\u00C6" 'Æ' >>> "\U0001F60A" '...

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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