Python - String isidentifier() Method

The isidentifier() string method returns True if the string's value is a valid identifier in Python, otherwise it returns False.

Identifiers are the names given to variables, functions, classes, modules etc, by following some rules specified by Python. These rules are as follows :

An identifier must start with an alphabet.
An identifier cannot not start with a digit.
An identifier must not contain a space or a comma(,) or even a dot(.)
An multi-word identifier can be separated by an underscore(_)
An identifier could be a mix of lowercase(a-z), uppercase(A-Z) alphabets, digits(0-9) or an underscore(_).
An identifier could be of any length.
An identifier cannot contain special characters like #,@,&,%.
Python is a case-sensitive language, hence identifier such as name is different from Name.
Python keywords i.e. reserved words, should not be used as identifiers.

Note : None of the string methods change the original string and only return a new string which reflects the change performed by the string method, hence the returned string must be stored or used(if needed to reflect the result), otherwise it is lost.

Signature of isidentifier()

The isidentifier() method has no parameters, so we don't have to worry about passing it some value.

# Signature of isidentifier() method 
isidentifier()

Calling isidentifier() method on a string object.

isidentifier()

# Python - Method isidentifier() Example



# Creating a string with a valid identifier
s1 = ('size')


# Printing the first string
print('Value of first string  : ', s1)


# Calling  the upper() method on first string 
print('Calling the isidentifier()() method  on first string : ', s1.isidentifier())




# Creating a string with a valid identifier
s2 = ('ink_price')

# Printing the second string
print('Value of second string  : ', s2)


# Calling  the isidentifier() method on second string  
print('Calling the isidentifier()() method on second string : ', s2.isidentifier())



# Creating a string with an invalid identifier
s3 = ('1stprice')

# Printing the third string
print('Value of third string  : ', s3)


# Calling  the isidentifier() method on third string  
print('Calling the isidentifier() method on third string : ', s3.isidentifier())

Output

Value of first string  :  size
Calling the isidentifier() method on first string :  True
Value of second string  :  ink_price
Calling the isidentifier() method on second string :  True
Value of third string  :  1stprice
Calling the isidentifier() method on third string :  False

Program Analysis

Calling the isidentifier() on the first string of valid identifier, returns False.
Calling the isidentifier() on the second string of valid identifier, returns False.
Calling the isidentifier() on the third string of invilaid indentifier(as it starts with a digit), returns False.

Another example of isidentifier() method

Let us see a few more examples of calling the isidentifier() method on all different forms of strings of valid and invalid identifiers.

# Python - Method isidentifier() Example



# Calling isidentifier() on a string of characters and digits i.e. a valid identifier
print('apple_price2'.isidentifier())


# Calling isidentifier() on a string of all upper case letters i.e. a valid identifier
print('ACTOR'.isidentifier())



# Calling isidentifier() on a string of all lower case values separated by space i.e. an invalid indentifier
print('The name'.isidentifier())



# Calling isidentifier() on a string of all lower case letters separated by dot i.e. an invalid identifier
print('the.address'.isidentifier())