reference.md

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Glossary

{:auto_ids} additive color model : A way to represent colors as the sum of contributions from primary colors such as red, green, and blue.

argument : A value given to a function or program when it runs. The term is often used interchangeably (and inconsistently) with parameter.

assertion : An expression which is supposed to be true at a particular point in a program. Programmers typically put assertions in their code to check for errors; if the assertion fails (i.e., if the expression evaluates as false), the program halts and produces an error message. See also: invariant, precondition, postcondition.

assign : To give a value a name by associating a variable with it.

body : (of a function): the statements that are executed when a function runs.

call stack : A data structure inside a running program that keeps track of active function calls.

case-insensitive : Treating text as if upper and lower case characters of the same letter were the same. See also: case-sensitive.

case-sensitive : Treating text as if upper and lower case characters of the same letter are different. See also: case-insensitive.

comment : A remark in a program that is intended to help human readers understand what is going on, but is ignored by the computer. Comments in Python, R, and the Unix shell start with a # character and run to the end of the line; comments in SQL start with --, and other languages have other conventions.

compose : To apply one function to the result of another, such as f(g(x)).

conditional statement : A statement in a program that might or might not be executed depending on whether a test is true or false.

comma-separated values : (CSV) A common textual representation for tables in which the values in each row are separated by commas.

default value : A value to use for a parameter if nothing is specified explicitly.

defensive programming : The practice of writing programs that check their own operation to catch errors as early as possible.

delimiter : A character or characters used to separate individual values, such as the commas between columns in a CSV file.

docstring : Short for "documentation string", this refers to textual documentation embedded in Python programs. Unlike comments, docstrings are preserved in the running program and can be examined in interactive sessions.

documentation : Human-language text written to explain what software does, how it works, or how to use it.

dotted notation : A two-part notation used in many programming languages in which thing.component refers to the component belonging to thing.

empty string : A character string containing no characters, often thought of as the "zero" of text.

encapsulation : The practice of hiding something's implementation details so that the rest of a program can worry about what it does rather than how it does it.

floating-point number : A number containing a fractional part and an exponent. See also: integer.

for loop : A loop that is executed once for each value in some kind of set, list, or range. See also: while loop.

function : A group of instructions (i.e., lines of code) that transform some input arguments to some output.

function call : A use of a function in another piece of software.

immutable : Unchangeable. The value of immutable data cannot be altered after it has been created. See also: mutable.

import : To load a library into a program.

in-place operators : An operator such as += that provides a shorthand notation for the common case in which the variable being assigned to is also an operand on the right hand side of the assignment. For example, the statement x += 3 means the same thing as x = x + 3.

index : A subscript that specifies the location of a single value in a collection, such as a single pixel in an image.

inner loop : A loop that is inside another loop. See also: outer loop.

integer : A whole number, such as -12343. See also: floating-point number.

invariant : An expression whose value doesn't change during the execution of a program, typically used in an assertion. See also: precondition, postcondition.

library : A family of code units (functions, classes, variables) that implement a set of related tasks.

loop variable : The variable that keeps track of the progress of the loop.

member : A variable contained within an object.

method : A function which is tied to a particular object. Each of an object's methods typically implements one of the things it can do, or one of the questions it can answer.

object : A collection of conceptually related variables (members) and functions using those variables (methods).

outer loop : A loop that contains another loop. See also: inner loop.

parameter : A variable named in the function's declaration that is used to hold a value passed into the call. The term is often used interchangeably (and inconsistently) with argument.

pipe : A connection from the output of one program to the input of another. When two or more programs are connected in this way, they are called a "pipeline".

postcondition : A condition that a function (or other block of code) guarantees is true once it has finished running. Postconditions are often represented using assertions.

precondition : A condition that must be true in order for a function (or other block of code) to run correctly.

regression : To re-introduce a bug that was once fixed.

return statement : A statement that causes a function to stop executing and return a value to its caller immediately.

RGB : An additive model that represents colors as combinations of red, green, and blue. Each color's value is typically in the range 0..255 (i.e., a one-byte integer).

sequence : A collection of information that is presented in a specific order. For example, in Python, a string is a sequence of characters, while a list is a sequence of any variable.

shape : An array's dimensions, represented as a vector. For example, a 5×3 array's shape is (5,3).

silent failure : Failing without producing any warning messages. Silent failures are hard to detect and debug.

slice : A regular subsequence of a larger sequence, such as the first five elements or every second element.

stack frame : A data structure that provides storage for a function's local variables. Each time a function is called, a new stack frame is created and put on the top of the call stack. When the function returns, the stack frame is discarded.

standard input : A process's default input stream. In interactive command-line applications, it is typically connected to the keyboard; in a pipe, it receives data from the standard output of the preceding process.

standard output : A process's default output stream. In interactive command-line applications, data sent to standard output is displayed on the screen; in a pipe, it is passed to the standard input of the next process.

string : Short for "character string", a sequence of zero or more characters.

syntax error : A programming error that occurs when statements are in an order or contain characters not expected by the programming language.

test oracle : A program, device, data set, or human being against which the results of a test can be compared.

test-driven development : The practice of writing unit tests before writing the code they test.

traceback : The sequence of function calls that led to an error.

tuple : An immutable sequence of values.

type : The classification of something in a program (for example, the contents of a variable) as a kind of number (e.g. floating-point, integer), string, or something else.

type of error : Indicates the nature of an error in a program. For example, in Python, an IOError to problems with file input/output. See also: syntax error.

while loop : A loop that keeps executing as long as some condition is true. See also: for loop.