Glossary

 

Access Control: Access control is the ability to selectively restrict who can access and or change variables and methods.

 

Algorithm: An algorithm is a precise, step by step plan for doing a computation.

 

Block: A block is multiple lines of code that are organized as a unit. If lines of code are sentences, blocks are paragraphs.

 

Boolean: A boolean is any expression which is either True or False.

 

Casting: Converting from one type to another is called casting. In a strongly typed language like Python, this requires using an explicit command.

 

Class: A class is a blueprint for creating a new data type. A class lets you write code to specify the features and powers of the new data type. An object is a particular copy of that data type.

 

Command Line Arguments: Command line arguments are arguments (or parameters) that are passed to the program from the command line.

 

Comments: Comments are written explanations in a code file that are ignored by the programming language. They are meant for other human programmers to read.

 

Constructor: A constructor is a method that builds a new object from a class blueprint.

 

CSS: CSS (short for cascading style sheets) is another language, used for styling HTML and other web content.  Style was historically dictated by HTML, but it got too complicated. CSS allows for more fine-grained control, and also allows the style portions of a web page to be separated from the content and markup (tag) portions.

 

Database: A relational database (usually just called a database except when comparing to other types) is a system for storing organized, persistent data. Persistent means the data is meant to last a long time. Organized means the data is meant to follow a well-defined pattern.

 

Definition: A function or class definition is the code that lets Python know what the function or class does. Python does not execute this code until the function is called or an object is created from the class.

 

Dictionary: A dictionary is a collection that lets you organize your data in pairs. There is a key, which you can use to look up a value.

 

Documentation: Documentation is the whole process of writing or generating clear explanations of your project and your code and making them accessible to future programmers.

 

Escape Sequence: Escape sequences are special character combinations that produce special characters inside strings. Escape sequences are usually composed of a backslash character followed by another character. The interpreter sees an escape sequence and replaces it with the appropriate special character.

 

Exception: An exception is an error that can be anticipated and possibly handled by a program.

 

Expression: An expression is any code that ultimately has a single value.

 

Evaluation: Evaluation is the act of reducing an expression to a single value.

 

File Handle: A file handle is an object that lets the program interact with a file. The file handle is provided by the operator system. The program does not generally know where the file lives on the hard drive; it simply uses the file handle to read or write data.

 

Function: Functions are little programs inside larger programs. They are usually written to do specific tasks. Functions may be called (or invoked) to do these tasks.

 

Guard: A guard is a boolean condition which must be True in order for a section of code to continue running. The boolean condition for a while loop is sometimes called the loop guard.

 

HTML: HTML, or HyperText Markup Language, is the basic language of the world wide web. Programmers write it (or more often write programs to write it). Servers send it to clients. Clients (web browsers, crawlers, and others) read it. Web browsers interpret it, rendering human readable web pages to users.

 

If Statement: The if Statement is a command that checks a condition, and either does one thing, or another, depending on the answer.  Think of the if statement like a branch in a river. Your program reaches the river branch, and either goes left or right.

 

Immutable: An immutable object does not change throughout the life of a program. Lists are mutable and can be changed. Tuples are immutable; a program cannot change the contents of a tuple.

 

Instantiation: Creating an object from a class blueprint is called instantiation. If there is a class that is the blueprint for an airplane, and we use it to create seventeen airplanes, we are instantiating seventeen airplanes from the class definition.

 

Iteration: Working through a collection element by element is called iterating. A for loop iterates over a collection, running a block of code once for each element of the collection. It is also acceptable to say that a loop loops or walks over a collection.

 

Iterator: An iterator is a mechanism to loop, or iterate, over a collection.

 

Keywords: Keywords are special words in the Python language. They can't be used as variable names, they do not have types, and they can't be given to other commands (like the type command). They are just fundamental building blocks of the language.

 

Library: A library is a tool or set of tools for a language, available as a self-contained package.

 

List: A list in Python is a collection of different things, in order. The items in the list are called list elements, or just elements.

 

List Comprehension: In Python, list comprehensions are short sentences that take old lists and make new sublists.

 

Machine Instructions: Machine instructions are instructions for computer hardware. In most cases, they directly instruct the computer's central processing unit, or CPU, to do things.

 

Method: A method is a function that is associated with an object (a piece of data, such as a string). The method is called on the object, and is assumed to automatically have access to the object.

 

Module: A module is Python's technology for implementing a library. A module is a collection of Python code, grouped together in a single place, for the purpose of being imported into other programs.

 

Mutable: A mutable object is one that can change throughout the life of a program. Lists are mutable and can be changed. Tuples are immutable; a program cannot change the contents of a tuple.

 

Nesting: Putting a block of code (like an if statement) inside another block of code is called nesting. An if statement inside another if statement is called a nested if statement.

 

Object: An object is a particular instance of a class. The class is the blueprint, and the objects are specific implementations.

 

Off By One Error: An off by one error is an error caused by one of the numbers in a calculation being 1 more or 1 less than it should be. This is especially common with string and list indexes, and with loops.

 

Operator: An operator is something that combines two items of the same type. Addition is an operator on the integers. The plus sign in 3 + 5 allows you to combine the integers 3 and 5.

 

Operator Overloading: When a symbol is used as an operator for two different types, it is overloaded. Operator overloading is the act of using a symbol to do different operations on different types of data.

 

Override: In the context of classes, overriding a method means replacing one of the parent's methods with a new version in the child class.

 

Parameter: The pieces of information you give (or pass) to a function are called parameters. The pieces of information the function gives you back are called return values. A function returns things to you, meaning it gives you back information. Parameters can be optional or required. If they are required, the function will not work without them.

 

Parameterization: Parameterization is the act of turning several similar functions with specific values into one function with an extra parameter.

 

Pseudocode: Pseudocode is code that isn't runnable, but is instead used to express the precise logic of a program to other humans.

 

Pseudo Random Number: A pseudo random number is a number which is generated according to a pattern but which has the appearance of having been generated randomly.

 

Python: Python is a language (like English, with a vocabulary and grammar rules) to write instructions for computers. It is also an interpreter program that reads those instructions and executes them.

 

Query: A query is the string that the user gives the search engine. The query is the thing the user wants found. Each individual word of the query is called a term.

 

Ranking: Ranking is the act of sorting those pages and choosing the "best" one for the user's query. Ranking is something of an art, in the sense that different people might disagree about what is the "best" result. Ranking is also a science, in the sense that it can be studied and improved by evidence.

 

Ranking Algorithm: A ranking algorithm is a program to assign a score to a web page (or document) for a particular search term.

 

Refactoring: Refactoring is the act of rewriting code, usually to be more readable and better organized, or to be shorter. Refactoring does not change the behavior of the code (the same inputs typically still lead to the same outputs). It changes the internal structure.

 

Regular Expressions: Regular expressions are a special language for pattern matching strings.

 

Retrieval: Retrieval is the act of looking through the index and finding all the pages that match a query.

 

Scope: Variables are not always available in all parts a program. The scope of a variable refers to the places where that variable is available for use. Variables defined in different places may have different scopes where they can be used. When an ambiguity is encountered, Python has well defined rules to resolve (or decide) which scope takes precedence, and thus, which variable (for instance, the list fruit or the parameter fruit) to use.

 

Search Index: A search index is a collection of web page data, stored long term. The search index is the content that a search engine knows and retrieves for users.

 

Static: In a class, variables and methods that do not depend on particular objects are called static. These are shared across all objects created with the class blueprint.

 

String: A string is text that is placed between quotes to let Python know that it is not part of the code. String is the data type for text.

 

Tag: In the HTML language (one of the languages of web pages), information is organized by tags. A tag is like a pair of brackets, enclosing a piece of information, and telling web browsers what type of information it is.

 

Terminal: A terminal (also known as a console, or the command line interface) is a text-based program where users can input text, and other programs can output text.

 

Test: A test is some code that runs other code, and checks to see if it has a particular result.

 

Test Driven Development: Test driven development is the act of writing tests first, to clearly define some expected outcomes, and then writing code to pass those tests.

 

Types: A type system is a way of classifying things in a programming language. Types are the different categories in this system. For example, a type system for food might be: fruits, vegetables, meat, dairy, and grains. Each of these is a type.

 

URL: URL stands for Uniform Resource Locator. URLs are strings that locate things, usually on the Internet.

 

User Agent String: A user agent string is a string you can use to identify yourself to other web sites, like a name. It is typically something related to the company or project the program is a part of.

 

Variables: Variables let you give names to your numbers, strings, and other data, and work with these names instead of repeatedly using the data itself.

 

Web Browser: A web browser is a program that downloads html code (and other web code) and uses it to render human usable web pages.

 

Web Crawler: A web crawler is a program that reads web pages and saves information about them for later use. A web crawler finds the links in web pages, and uses these to find more web pages to crawl. Typically a web crawler is started with a set of seed URLs, and follows a trail from these to a much larger set of web pages.

 

Whitespace: Whitespace is the empty space around code. Some programming languages are whitespace agnostic, meaning they are not concerned whether the whitespace is arranged in a particular way. Python requires certain forms of whitespace (such as indentation for blocks) to be formatted in specific ways.