Identifiers and Keywords

What are Identifiers?

They are user-defined names that are used to identify entities such as classes, functions, variables, and so on. They're utilised to distinguish one object from another.

An identifier is a combination of digits, characters, and underscores. The first letter of an identifier can not be a character or digit. 

Python is case sensitive; hence identifiers in Python are also case sensitive. For example, Var and var are two different identifiers. 

Also see, Python Operator Precedence

Rules for naming Identifier

• A combination of digits, underscores, and lowercase or uppercase characters can be used to create identifiers.
• Identifiers should not contain spaces in between. 
• A keyword should not be used as an identifier. 
• Special symbols other than underscore should not be used.
• Digits must not be present at the beginning of an identifier. 

Examples of correct identifier names are var, _var, _var9, _9var, etc. 

Examples of incorrect identifier names are 9var, @var, var@, var1@, etc. 

Function to check a valid identifier

There is an isidentifier() method present in Python, which checks if a string is a valid identifier or not. The function returns True if the string is a valid identifier, else it returns False.

var = "a9_bc"
print(var.isidentifier())
var = "_abc9"
print(var.isidentifier())
var = "9_abc"
print(var.isidentifier())

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Output:

True
True
False

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Example 1:

The below example shows that keywords cannot be used as identifiers. 

#using keyword as identifier
True=1

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Output:

True=1
    ^
SyntaxError: cannot assign to True

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Example 2:

The below example shows usage of yield, for, in, else, elif, fun, def keyword. 

def generatorFun():
    for i in range(5):
        yield i

obj = generatorFun()
for i in obj:
    if i==0:
        print("i is zero")
    elif i==1:
        print("i is one")
    else:
        print("i is not zero neither one")

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Output:

i is zero
i is one
i is not zero neither one
i is not zero neither one
i is not zero neither one

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Example 3:

The below example shows usage of try, except, def, return keyword. 

def fun():
    var = 0
    try :
        divideRes = 1/var
        return divideRes
    except:
        print("Error")
        return -1

var = fun()
print(var)

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Output:

Error
-1

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Example 4:

The below example shows usage of global, def, del keyword. 

l = [1,2,3]
def fun():
    global l
    del(l[1])

print(*l)
fun()
print(*l)

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Output:

1 2 3
1 3

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Example 5:

The below example shows the usage of the assert keyword. 

def fun(num1, num2):
    assert (num2!=0), "Divisor is zero"
    num1 = num1 / num2
    return num1

res = fun(1,0)
print(res)

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Output:

AssertionError: Divisor is zero

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Frequently Asked Questions

1. How to check if an identifier is valid or not?
   Python contains the isidentifier() method, which can be used to check if a string is a valid identifier or not. It returns True if it is valid, else returns False. 
    
2. What is the difference between keyword and identifier?
   Keywords are a predefined and reserved set of words in Python which holds a special meaning, while identifiers are a name given to a variable, class, or function.
    
3. Can keywords be used as identifier names?
   No. Keywords are reserved and cannot be used as an identifier name. 

Key Takeaways

Congratulations on making it this far.

In this blog, we understood what keywords and identifiers in Python are.  We also saw different keywords present in Python and learned about their importance. 

If you want to become proficient with Python programming, I suggest you take the Coding Ninjas Python Course, which will teach Python basics with Data Structures and Algorithms.