Python Language: Difference between revisions

From NovaOrdis Knowledge Base
Jump to navigation Jump to search
Line 24: Line 24:
Variables are requests to Python to allocate memory and place something in in, and associate a label (the '''variable name''') to it. Variables are declared and assigned a value though an [[#Assignment_Statement|assignment statement]].
Variables are requests to Python to allocate memory and place something in in, and associate a label (the '''variable name''') to it. Variables are declared and assigned a value though an [[#Assignment_Statement|assignment statement]].
==Variable Naming Rules==
==Variable Naming Rules==
Variable names are case sensitive. Variable names can start with letters or underscore ('_') - but underscores should be generally avoided because Python tends to use underscores for its internal purposes. The rest of the variable name can be letters, numbers and underscores.
Variable names are case sensitive. Variable names can start with letters or underscore ('_') - but underscores should be generally avoided because Python tends to use underscores for its internal purposes. The rest of the variable name can be letters, numbers and underscores. No other characters are allowed.


=Statements=
=Statements=

Revision as of 05:29, 22 May 2021

Internal

Reserved Words

Reserved words can only be used to mean the thing Python expects them to mean. They cannot be used as variable names, function names, class names, or identifiers.

False class return is finally
None if for lambda continue
True def from while nonlocal
and del global not with
as elif try or yield
assert else import pass
break except in raise

Constants

Constants are fixed values, they do not change throughout the program. Constants can be numeric, or strings, which can be single quoted or double quoted.

Variables

Variables are requests to Python to allocate memory and place something in in, and associate a label (the variable name) to it. Variables are declared and assigned a value though an assignment statement.

Variable Naming Rules

Variable names are case sensitive. Variable names can start with letters or underscore ('_') - but underscores should be generally avoided because Python tends to use underscores for its internal purposes. The rest of the variable name can be letters, numbers and underscores. No other characters are allowed.

Statements

In Python 2, print used to be a statement, while in Python 3, print() is a function.

Assignment Statement

The assignment statement assigns a value to a variable.

x = 1

The assignment accepts expressions:

x = x + 1

Functions

Expressions

Operators

+, = are operators.

Identifiers

Python Script

A Python program file is called a Python script - a stored set of instructions that can be handed over to the Python interpreter. Python scripts have the .py extensions.

Flow Control

Sequential Steps

Sequential steps have the same indentation level.

Conditional Steps

if x < 10:
  print('something')

Loops

n = 5
while n > 0:
  print(n)
  n = n - 1

Loops have iteration variables, which are initialized, checked and changed within the loop.

Functions

Classes

Organizatorium

Nesting