Glossary
Here is a glossary of commonly used terms within these notes. For a more complete glossary see the set provided in the Python documentation here (any descriptions in quotation marks are lifted directly from that page).
%¶
The percent sign is used for modular arithmetic,
i.e., it returns the integer remainder after division of one number by another. E.g., 10 % 3 gives
1.
*¶
The multiplication operator, i.e., used for getting the product of two values/objects. An asterisk is used rather than the standard cross.
**¶
The exponentiation operator, i.e., used for raising a value to the power of an
exponent. E.g., in x = 2 ** 5 the value of 2 is raised to the power of 5. Integer or floating
point numbers can be used for both the base and exponent.
+¶
The addition operator, i.e., used for getting the sum of two values/objects.
-¶
The subtraction operator, i.e., used for getting the difference between two values/objects.
/¶
The division operator, i.e., used for getting the quotient of two values/objects.
@¶
The "at" symbol has two uses. It can be used as an operator to perform matrix multiplication. Alternatively, it is used when defining a decorator function wrapping another function.
Alias¶
An alternative, and generally shorter, way of referring to a namespace. When importing
a module, the module's namespace can be aliased using the as keyword, e.g., in import numpy as
np the numpy namespace has been aliased to np, which can then be used within the code in place
of numpy.
Argument¶
An argument is a variable or value that is passed to a function, so that it can be used within the function.
Attribute¶
An attribute is "A value associated with an object which is referenced by name using dotted
expressions. For example, if an object o has an attribute a it would be referenced as
o.a". Attributes can be variables within
a class (data attributes) or methods.
Boolean¶
A data type that can take one of two possible values, "True" or "False", which can be used when
performing Boolean algebra, i.e., evaluating
logical expressions. In Python, Boolean variables have the type "bool".
Built-in¶
Something, for example a function or module, that is defined within any Python installation and is therefore available to use in any Python code.
Call¶
Call refers to using a function. For example, if you ran print("Hello") you could also say that
you "called" the print function.
Child¶
A class that inherits attributes from a parent class, sometimes known as a subclass.
Class¶
Class attribute¶
A data attributes) of a class that is owned by the class itself, and so will have the same value for all instances of the class.
Class instance¶
A instance of a class is an object created from a class, e.g., in x = int(1) the variable x is
an instance of the int class.
Class method¶
A class method is "A function which is defined inside a class body."
Class variable¶
Command line¶
The line in a terminal into which you type a command. In a Python session, the command
line will start with the command prompt >>> and contain a flashing cursor.
Command prompt¶
The starting characters on the command line in a terminal. In a Python
session, the command prompt will be >>> and contain a flashing cursor.
Data attribute¶
This is a class attribute that refers to a data variable within the class.
Decorator¶
A decorator is "A function returning another
function". To define a function that is
wrapped in another "decorator" function, the line before the function definition should contain
@decoratorname, where decoratorname is the name of the decorating function.
Directory¶
A named location on a disk drive which contains other files or directories. The word folder and directory may be used interchangeably and in a file explorer they may be represented with a , or similar icon.
Escape character¶
In a Python string the forward slash \ is an escape
character. This means that in certain cases the
combination of the forward slash and the following character have a different meaning, e.g., \n
will be interpreted as starting a new line. The also allow you to insert "illegal" characters into a
string, e.g., to use a quotation mark in a string defined within quotation marks you can use x =
"They said \"Hello\"". Some common Python escape characters are listed
here.
Exception¶
An exception is an error detected in a code during its execution. When exceptions are encountered the code will, generally, fail and an error message will be printed to screen. Python has a set of standard exceptions dependent on the "type" of error encountered.
File extension¶
This is the end part of a file's name, after the full stop, that defines type of file that it is.
For example, in myscript.py the file extension is py and shows this is a Python file, or in
mydocument.docx the file extension docx shows this is a Microsoft Word document.
float¶
A class for defining a floating point number. Python automatically
recognises variables set with numbers containing decimal places or exponential notation to be
floating point numbers, e.g., in y = -9.7 the variable y will be a float type, which is
equivalent to explicitly saying y = float(-9.7).
Floating point number¶
A floating point number is any real non-integer number. The "floating point" refers to the decimal point in the number, which can "float", i.e., be placed anywhere between the other digits in the number.
Folder¶
A synonym for a directory, i.e., a name location on a disk drive in which other files or folder are stored.
Function¶
A function is a piece of code that can take in variable arguments, perform some
operations, and return an output. In Python, functions are defined using the def
keyword.
Function attribute¶
This is a class attribute that refers to a function (also known as a class method).
Immutable¶
An object that cannot be changed after it is created. The opposite is something that is mutable.
Indent¶
Using whitespace (a series of spaces or tabs) to place a code block away from the left hand edge of the screen.
Index¶
The location of a value within an array-like object, e.g., a list. Indices start at 0 for the location of the first value, and end at one less than the length of the object.
Instance attribute¶
A data attributes) of a class that has a value specific for each instance of that class, e.g., as defined by the user.
int¶
A class for defining integer numbers. Python automatically recognises variables set with integer
number values to be integers, e.g., in x = 1 the variable x will be an int type, which is
equivalent to explicitly saying x = int(1).
Iterable¶
An iterable is "[a]n object capable of returning its members one at a time.", for example a list.
Keyword¶
In Python there are a set of reserved words that cannot be used for variable, function or class names as they already have a defined usage. These are keywords.
Keyword argument¶
A keyword argument to a function is an argument defined by a keyword identifier and
value pair separated by an equals sign. The value after the equals sign provides a default value
used within the function if the keyword is not used in the function call, e.g., in def func(x=2):
the argument x is the keyword and 2 is the default value it takes. Keyword arguments can be
passed to the function in any order provided the keyword identifier is used, if not used then the
arguments must be given in the order in the function definition.
Linting¶
Linting is the automatic checking of code, using an analysis tool called a linter, for any errors or bugs. In Python, these might be include unclosed brackets, incompatible indents, missing colons are function definitions, etc.
Method¶
In Python, a method is how a function within a class is referred to.
Module¶
"A module is a file containing Python definitions and statements."
Mutable¶
An object that is changeable after created. The opposite is something that is immutable.
Namespace¶
Most generally: "A namespace is a mapping from names to
objects". However, a
common use of namespace is at the module level and refers to using something (e.g., a
function) within a module by explicitly declaring the module's name to avoid ambiguity with other
potentially identically named objects. E.g., using the sin function with the math module: x =
math.sin(1.0).
Object¶
In Python, object's are the building blocks of a code; everything is an object! They can contain data (variables) and ways of manipulating data (functions). Objects have a type which is defined using their class. Generally, any instance of a class is an object.
Operator¶
An operator generally refers to one of the mathematical binary
operators of addition +, subtraction -,
multiplication *, and division /, used in elementary
arithmetic.
Package¶
A Python module, or set of modules, that have been "packaged" together into an installable piece of software. Once a package is installed you can import the modules from within it.
Parent¶
A class who's attributes will be inherited by a new child class. This is sometimes known as a superclass.
Path¶
The location of a file within a file system is given by its path, e.g.,
C:\Users\username\Project\myfile.py is the path to the file myfile.py. Having the path starting
from the drive letter, or root directory, is also known as the "absolute path". Paths can also be
relative to the current directory, which is known as a "relative path".
Positional argument¶
A positional argument to a function is an argument defined by a name without the equals
sign, e.g., in def func(a, b): both a and b are positional arguments. When using the function
the positional arguments must be passed in the order that they are given in the function definition.
They must come before any keyword arguments.
PyPI¶
A repository of shared Python packages that are installable using the Python
package installer pip.
Script¶
A script is a file containing code that is generally used to perform just one job and is standalone
(i.e., it can be run on its own without having to be run by a different code). A Python script file
has the file extension py.
Shell¶
A program that provides a command line interface with an operating system, often run within a terminal.
Slice¶
Slices are a way of accessing multiple index values using the colon : notation, e.g., start:stop
or start:stop:step, where start is the index of the first value to return, stop is the index
one after that of last value to return, and step is the integer step between indexes of returned
value. The slice built-in function can also
be used to generate a slice.
String¶
In programming a string generally refers to a variable type that holds some text, i.e.,
a series of alphanumeric characters. In Python, strings are defined by text enclosed within
apostrophes, quotation marks, or a series of three apostrophes/quotation marks, e.g., x = 'Hello',
x = "Hello" and x = """Hello""" are all equivalent ways of defining a string.
subclass¶
A synonym for a child class.
superclass¶
A synonym for a parent class.
Syntax¶
In programming languages "syntax" refers to the specific required structure, or grammar, of the language for it to be understood by the computer.
Syntax highlighting¶
This is the automatic highlighting of text within a code, via font colour, weight or italicisation, that uses recognised syntax, formatting or keywords for a given programming language. Text editors with syntax highlighting can often recognise the language and highlight appropriately.
Terminal¶
A text-based window for running commands via a command-line prompt in a shell. In Windows, a common terminal program is PowerShell.
Traceback¶
This is a message returned after encountering an exception that reports the function calls made at the point where it encountered the error. This may be nested through several layers of functions.
Type¶
In Python, variables have a type, which is the kind of thing (e.g., an integer or a string) that the variable represents as defined by its class. Often "type" and "class" will be used interchangeably.
Variable¶
A variable in Python is a named object (or named class instance), e.g., in x = 2.9 a variable
called x has been created that pointed to the float number object 2.9.
Virtual environment¶
A virtual environment is an isolated environment used for Python projects. It can have a specific version of Python and specific versions of various packages as required for the project. These are isolated and independent from any versions of the packages that may be installed globally on the computer.
Whitespace¶
Spaces Space, tabs Tab and carriage returns Enter/new lines within a document or string and known as whitespace.