Python Tutorial - Keywords and Identifiers

Jinku Hu Sep 17, 2020

Python Keywords
Python Identifiers

Python Tutorial - Keywords and Identifiers

In this section, We will discuss Python keywords and identifiers.

Python Keywords

Keywords are the predefined words that have special meaning and that cannot be used to name any variable, function, class, etc. Keywords are also called reserved words that are actually reserved for special purposes.

Python has 33 case-sensitive keywords. Most of them except True, False and None are written in lowercase. The following is the list of Python keywords:

Keywords	Description
`class`	defines a class in Python OOP.
`as`	used with `with as` when you want to execute two operations together as a pair
`and`	is a logical and operator. `and` will generate `True` when both conditions are true else `False` will be returned.
`assert`	ensures if a condition is `True`
`break`	is used to break flow of control while working with looping construct on the basis of certain condition.
`continue`	skips the current iteration of a looping construct on the basis of a condition.
`def`	defines a function in Python
`del`	deletes any reference of an object.
`elif`	represents else if construct
`else`	else is block of statements to be executed when a condition with if becomes `False`. (else is optional)
`except`	handles exceptions (run time errors)
`finally`	A `finally` clause is always executed before leaving the try statement, whether an exception has occurred or not
`for`	represents `for` loop
`from`	used with import to import any function, program from a module
`global`	declares a global variable
`if`	represents the `if` statement, the body of which is executed when condition is `True`
`import`	imports a function, class, variable from a module
`in`	1. Membership check Operator 2. Traversing a sequence object in a `for` loop
`is`	checks the equivalence of two quantities
`lambda`	creates `lambda` function (anonymous function)
`not`	is a unary operator (operates on one operand). It negates the value `True` to `False` and vice versa.
`or`	is a logical or operator. `or` will generate `True` when any of the condition is true else `False` will be returned.
`pass`	represents a null statement. pass is used as a placeholder in Python.
`raise`	raises an exception
`return`	returns value from a function
`try`	represents a block in which there are some lines of a code that can result in an exception
`while`	represents `while` loop
`with`	ensures that a code is clarified (all exceptions handled using try catch)
`yield`	return generator (generates one item in each iteration) from a function
`nonlocal`	declares non-local variable when working with nested function. nonlocal variable in nested function is known to outer function.
`None`	represents a `null` value
`True`	A Boolean value returned when a Boolean expression is evaluated.
`False`	A Boolean value returned when a Boolean expression is evaluated.

Python Identifiers

Identifiers are names of functions, variables, class, etc. Reserved words are not allowed to be the names of identifiers.

Rules for Naming Identifiers

An identifier can have letters (both uppercase or lowercase), digits (0 to 9) or underscore (_), for example, last_name1, my_first_name and CapName are legal identifiers.
You cannot use digits to start an identifier, for example, 1last_name is an illegal identifier.
Keywords are not allowed to be the names of identifiers.
Special symbols such as $, !, @, #, %, etc. are not allowed in an identifier.
Python identifier has no length limitation.
Blank spaces are not allowed.

Points to Ponder

As Python is case sensitive meaning that uppercase and lowercase variables are different. So last_name and LAST_name are two different variables.
Use meaningful names for variables to increase the readability of your codes.
If your variable contains multiple words, they should be separated by underscore.
Or you can use camel case to separate multiple words, that is, the first letter of each word to be upper-case, for example, CapitalizedWords.

Author: Jinku Hu

Founder of DelftStack.com. Jinku has worked in the robotics and automotive industries for over 8 years. He sharpened his coding skills when he needed to do the automatic testing, data collection from remote servers and report creation from the endurance test. He is from an electrical/electronics engineering background but has expanded his interest to embedded electronics, embedded programming and front-/back-end programming.

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