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...

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...

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...

Functions and Modules | Core Python 3.8

Functions In the “Numbers and Expressions” section, I used the exponentiation operator (**) to calculate powers. The fact is that you can use a function instead, called pow. >>> 2 ** 3 8 >>> pow(2, 3) 8 A function is like a little program that you can use to perform a specific action. Python has a lot of functions that can do many wonderful things. In fact, you can make your own functions, too (more about that later); therefore, we often refer to standard functions such as pow as built-in functions. Using a function as I did in the preceding example is called calling the function. You supply it with arguments (in this case, 2 and 3), and it returns a value to you. Because it returns a value, a function call is simply another type of expression, like the arithmetic expressions discussed earlier in this chapter.6 In fact, you can combine function calls and operators to create more complicated expressions (like I did...

Exceptions | Core Python 3.8

When writing computer programs, it is usually possible to discern between a normal course of events and something that’s exceptional (out of the ordinary). Such exceptional events might be errors (such as trying to divide a number by zero) or simply something you might not expect to happen very often. To handle such exceptional events, you might use conditionals everywhere the events might occur (for example, have your program check whether the denominator is zero for every division). However, this would not only be inefficient and inflexible but would also make the programs illegible. You might be tempted to ignore these exceptional events and just hope they won’t occur, but Python offers an exception-handling mechanism as a powerful alternative. In this tutorial, you’ll learn how to create and raise your own exceptions, as well as how to handle exceptions in various ways. What Is an Exception? To represent exceptional conditions, Python uses exception obj...

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