Today we will learn about Python keywords and identifiers. Earlier we learned how to install python and get started with it in python tutorial for beginners.
Well simply, python keywords are the words that are reserved. That means you can’t use them as name of any entities like variables, classes and functions.
So you might be thinking what are these keywords for. They are for defining the syntax and structures of Python language.
You should know there are 33 keywords in Python programming language as of writing this tutorial. Although the number can vary in course of time. Also keywords in Python is case sensitive. So they are to be written as it is. Here is a list of all keywords in python programming.
If you look at all the keywords and try to figure out all at once, you will be overwhelmed. So for now just know these are the keywords. We will learn their uses respectively. You can get the list of python keywords through python shell help.
>>> help() Welcome to Python 3.6's help utility! help> keywords Here is a list of the Python keywords. Enter any keyword to get more help. False def if raise None del import return True elif in try and else is while as except lambda with assert finally nonlocal yield break for not class from or continue global pass help>
Below is a simple example showing usage of if-else in python program.
var = 1; if(var==1): print("odd") else: print("even")
When we run above program, python understands the if-else block because of fixed keywords and syntax and then do the further processing.
Python Identifier is the name we give to identify a variable, function, class, module or other object. That means whenever we want to give an entity a name, that’s called identifier.
Sometimes variable and identifier are often misunderstood as same but they are not. Well for clarity, let’s see what is a variable?
Variable in Python
A variable, as the name indicates is something whose value is changeable over time. In fact a variable is a memory location where a value can be stored. Later we can retrieve the value to use. But for doing it we need to give a nickname to that memory location so that we can refer to it. That’s identifier, the nickname.
Rules for writing Identifiers
There are some rules for writing Identifiers. But first you must know Python is case sensitive. That means Name and name are two different identifiers in Python. Here are some rules for writing Identifiers in python.
- Identifiers can be combination of uppercase and lowercase letters, digits or an underscore(_). So myVariable, variable_1, variable_for_print all are valid python identifiers.
- An Identifier can not start with digit. So while variable1 is valid, 1variable is not valid.
- We can’t use special symbols like !,#,@,%,$ etc in our Identifier.
- Identifier can be of any length.
Though these are hard rules for writing identifiers, also there are some naming conventions which are not mandatory but rather good practices to follow.
- Class names start with an uppercase letter. All other identifiers start with a lowercase letter.
- Starting an identifier with a single leading underscore indicates the identifier is private.
- If the identifier starts and ends with two underscores, than means the identifier is language-defined special name.
- While c = 10 is valid, writing count = 10 would make more sense and it would be easier to figure out what it does even when you look at your code after a long time.
- Multiple words can be separated using an underscore, for example this_is_a_variable.
Here’s a sample program for python variables.
myVariable="hello world" print(myVariable) var1=1 print(var1) var2=2 print(var2)
If you run the program, the output will be like below image.
So, that’s it for today. In the next tutorial we will learn about Python Statements and Comments. Till then #happy_coding 🙂