bug

An error in a program.

central processing unit

The heart of any computer. It is what runs the software that we write; also called "CPU" or "the processor".

compile

To translate a program written in a high-level language into a low-level language all at once, in preparation for later execution.

high-level language

A programming language like Python that is designed to be easy for humans to read and write.

interactive mode

A way of using the Python interpreter by typing commands and expressions at the prompt.

interpret

To execute a program in a high-level language by translating it one line at a time.

low-level language

A programming language that is designed to be easy for a computer to execute; also called "machine code" or "assembly language".

machine code

The lowest-level language for software, which is the language that is directly executed by the central processing unit (CPU).

main memory

Stores programs and data. Main memory loses its information when the power is turned off.

parse

To examine a program and analyze the syntactic structure.

portability

A property of a program that can run on more than one kind of computer.

print function

An instruction that causes the Python interpreter to display a value on the screen.

problem solving

The process of formulating a problem, finding a solution, and expressing the solution.

program

A set of instructions that specifies a computation.

prompt

When a program displays a message and pauses for the user to type some input to the program.

secondary memory

Stores programs and data and retains its information even when the power is turned off. Generally slower than main memory. Examples of secondary memory include disk drives and flash memory in USB sticks.

semantics

The meaning of a program.

semantic error

An error in a program that makes it do something other than what the programmer intended.

source code

A program in a high-level language.

assignment

A statement that assigns a value to a variable.

concatenate

To join two operands end to end.

comment

Information in a program that is meant for other programmers (or anyone reading the source code) and has no effect on the execution of the program.

evaluate

To simplify an expression by performing the operations in order to yield a single value.

expression

A combination of variables, operators, and values that represents a single result value.

floating point

A type that represents numbers with fractional parts.

integer

A type that represents whole numbers.

keyword

A reserved word that is used by the compiler to parse a program; you cannot use keywords like if, def, and while as variable names.

mnemonic

A memory aid. We often give variables mnemonic names to help us remember what is stored in the variable.

modulus operator

An operator, denoted with a percent sign (%), that works on integers and yields the remainder when one number is divided by another.

operand

One of the values on which an operator operates.

operator

A special symbol that represents a simple computation like addition, multiplication, or string concatenation.

rules of precedence

The set of rules governing the order in which expressions involving multiple operators and operands are evaluated.

statement

A section of code that represents a command or action. So far, the statements we have seen are assignments and print expression statement.

string

A type that represents sequences of characters.

type

A category of values. The types we have seen so far are integers (type int), floating-point numbers (type float), and strings (type str).

value

One of the basic units of data, like a number or string, that a program manipulates.

variable

A name that refers to a value.

body

The sequence of statements within a compound statement.

boolean expression

An expression whose value is either True or False.

branch

One of the alternative sequences of statements in a conditional statement.

chained conditional

A conditional statement with a series of alternative branches.

comparison operator

One of the operators that compares its operands: ==, !=, >, <, >=, and <=.

conditional statement

A statement that controls the flow of execution depending on some condition.

condition

The boolean expression in a conditional statement that determines which branch is executed.

compound statement

A statement that consists of a header and a body. The header ends with a colon (:). The body is indented relative to the header.

guardian pattern

Where we construct a logical expression with additional comparisons to take advantage of the short-circuit behavior.

logical operator

One of the operators that combines boolean expressions: and, or, and not.

nested conditional

A conditional statement that appears in one of the branches of another conditional statement.

traceback

A list of the functions that are executing, printed when an exception occurs.

short circuit

When Python is part-way through evaluating a logical expression and stops the evaluation because Python knows the final value for the expression without needing to evaluate the rest of the expression.

algorithm

A general process for solving a category of problems.

argument

A value provided to a function when the function is called. This value is assigned to the corresponding parameter in the function.

body

The sequence of statements inside a function definition.

composition

Using an expression as part of a larger expression, or a statement as part of a larger statement.

deterministic

Pertaining to a program that does the same thing each time it runs, given the same inputs.

dot notation

The syntax for calling a function in another module by specifying the module name followed by a dot (period) and the function name.

flow of execution

The order in which statements are executed during a program run.

fruitful function

A function that returns a value.

function

A named sequence of statements that performs some useful operation. Functions may or may not take arguments and may or may not produce a result.

function call

A statement that executes a function. It consists of the function name followed by an argument list.

function definition

A statement that creates a new function, specifying its name, parameters, and the statements it executes.

function object

A value created by a function definition. The name of the function is a variable that refers to a function object.

header

The first line of a function definition.

import statement

A statement that reads a module file and creates a module object.

module object

A value created by an import statement that provides access to the data and code defined in a module.

parameter

A name used inside a function to refer to the value passed as an argument.

pseudorandom

Pertaining to a sequence of numbers that appear to be random, but are generated by a deterministic program.

return value

The result of a function. If a function call is used as an expression, the return value is the value of the expression.

void function

A function that does not return a value.

accumulator

A variable used in a loop to add up or accumulate a result.

counter

A variable used in a loop to count the number of times something happened. We initialize a counter to zero and then increment the counter each time we want to "count" something.

decrement

An update that decreases the value of a variable.

initialize

An assignment that gives an initial value to a variable that will be updated.

increment

An update that increases the value of a variable (often by one).

infinite loop

A loop in which the terminating condition is never satisfied or for which there is no terminating condition.

iteration

Repeated execution of a set of statements using either a function that calls itself or a loop.

counter

A variable used to count something, usually initialized to zero and then incremented.

empty string

A string with no characters and length 0, represented by two quotation marks.

format operator

An operator, %, that takes a format string and a tuple and generates a string that includes the elements of the tuple formatted as specified by the format string.

format sequence

A sequence of characters in a format string, like %d, that specifies how a value should be formatted.

format string

A string, used with the format operator, that contains format sequences.

flag

A boolean variable used to indicate whether a condition is true or false.

invocation

A statement that calls a method.

immutable

The property of a sequence whose items cannot be assigned.

index

An integer value used to select an item in a sequence, such as a character in a string.

item

One of the values in a sequence.

method

A function that is associated with an object and called using dot notation.

object

Something a variable can refer to. For now, you can use "object" and "value" interchangeably.

search

A pattern of traversal that stops when it finds what it is looking for.

sequence

An ordered set; that is, a set of values where each value is identified by an integer index.

slice

A part of a string specified by a range of indices.

traverse

To iterate through the items in a sequence, performing a similar operation on each.

catch

To prevent an exception from terminating a program using the try and except statements.

newline

A special character used in files and strings to indicate the end of a line.

Pythonic

A technique that works elegantly in Python. "Using try and except is the Pythonic way to recover from missing files".

Quality Assurance

A person or team focused on insuring the overall quality of a software product. QA is often involved in testing a product and identifying problems before the product is released.

text file

A sequence of characters stored in permanent storage like a hard drive.

aliasing

A circumstance where two or more variables refer to the same object.

delimiter

A character or string used to indicate where a string should be split.

element

One of the values in a list (or other sequence); also called items.

equivalent

Having the same value.

index

An integer value that indicates an element in a list.

identical

Being the same object (which implies equivalence).

list

A sequence of values.

list traversal

The sequential accessing of each element in a list.

nested list

A list that is an element of another list.

object

Something a variable can refer to. An object has a type and a value.

reference

The association between a variable and its value.

dictionary

A mapping from a set of keys to their corresponding values.

hashtable

The algorithm used to implement Python dictionaries.

hash function

A function used by a hashtable to compute the location for a key.

histogram

A set of counters.

implementation

A way of performing a computation.

item

Another name for a key-value pair.

key

An object that appears in a dictionary as the first part of a key-value pair.

key-value pair

The representation of the mapping from a key to a value.

lookup

A dictionary operation that takes a key and finds the corresponding value.

nested loops

When there are one or more loops "inside" of another loop. The inner loop runs to completion each time the outer loop runs once.

value

An object that appears in a dictionary as the second part of a key-value pair. This is more specific than our previous use of the word "value".

brittle code

Code that works when the input data is in a particular format but is prone to breakage if there is some deviation from the correct format. We call this "brittle code" because it is easily broken.

greedy matching

The notion that the "+" and "*" characters in a regular expression expand outward to match the largest possible string.

grep

A command available in most Unix systems that searches through text files looking for lines that match regular expressions. The command name stands for "Generalized Regular Expression Parser".

regular expression

A language for expressing more complex search strings. A regular expression may contain special characters that indicate that a search only matches at the beginning or end of a line or many other similar capabilities.

wild card

A special character that matches any character. In regular expressions the wild-card character is the period.

BeautifulSoup

A Python library for parsing HTML documents and extracting data from HTML documents that compensates for most of the imperfections in the HTML that browsers generally ignore. You can download the BeautifulSoup code from www.crummy.com.

port

A number that generally indicates which application you are contacting when you make a socket connection to a server. As an example, web traffic usually uses port 80 while email traffic uses port 25.

scrape

When a program pretends to be a web browser and retrieves a web page, then looks at the web page content. Often programs are following the links in one page to find the next page so they can traverse a network of pages or a social network.

socket

A network connection between two applications where the applications can send and receive data in either direction.

spider

The act of a web search engine retrieving a page and then all the pages linked from a page and so on until they have nearly all of the pages on the Internet which they use to build their search index.

API

Application Program Interface - A contract between applications that defines the patterns of interaction between two application components.

ElementTree

A built-in Python library used to parse XML data.

JSON

JavaScript Object Notation. A format that allows for the markup of structured data based on the syntax of JavaScript Objects.

SOA

Service-Oriented Architecture. When an application is made of components connected across a network.

XML

eXtensible Markup Language. A format that allows for the markup of structured data.

attribute

A variable that is part of a class.

class

A template that can be used to construct an object. Defines the attributes and methods that will make up the object.

child class

A new class created when a parent class is extended. The child class inherits all of the attributes and methods of the parent class.

constructor

An optional specially named method (init) that is called at the moment when a class is being used to construct an object. Usually this is used to set up initial values for the object.

destructor

An optional specially named method (del) that is called at the moment just before an object is destroyed. Destructors are rarely used.

inheritance

When we create a new class (child) by extending an existing class (parent). The child class has all the attributes and methods of the parent class plus additional attributes and methods defined by the child class.

method

A function that is contained within a class and the objects that are constructed from the class. Some object-oriented patterns use 'message' instead of 'method' to describe this concept.

object

A constructed instance of a class. An object contains all of the attributes and methods that were defined by the class. Some object-oriented documentation uses the term 'instance' interchangeably with 'object'.

parent class

The class which is being extended to create a new child class. The parent class contributes all of its methods and attributes to the new child class.

attribute

One of the values within a tuple. More commonly called a "column" or "field".

constraint

When we tell the database to enforce a rule on a field or a row in a table. A common constraint is to insist that there can be no duplicate values in a particular field (i.e., all the values must be unique).

cursor

A cursor allows you to execute SQL commands in a database and retrieve data from the database. A cursor is similar to a socket or file handle for network connections and files, respectively.

database browser

A piece of software that allows you to directly connect to a database and manipulate the database directly without writing a program.

foreign key

A numeric key that points to the primary key of a row in another table. Foreign keys establish relationships between rows stored in different tables.

index

Additional data that the database software maintains as rows and inserts into a table to make lookups very fast.

logical key

A key that the "outside world" uses to look up a particular row. For example in a table of user accounts, a person's email address might be a good candidate as the logical key for the user's data.

normalization

Designing a data model so that no data is replicated. We store each item of data at one place in the database and reference it elsewhere using a foreign key.

primary key

A numeric key assigned to each row that is used to refer to one row in a table from another table. Often the database is configured to automatically assign primary keys as rows are inserted.

relation

An area within a database that contains tuples and attributes. More typically called a "table".

tuple

A single entry in a database table that is a set of attributes. More typically called "row".