Identifiers in Python Programs
In this tutorial, you will learn the concept of identifiers in Python programs.
A name in the Python program is called an identifier. It can be a class name or function name or module name or variable name. Example, a = 10
Rules to define identifiers in Python:
1. The only allowed characters in Python are,
- alphabet symbols (either lower case or upper case) and digits. That is (a to z or A to Z or 0 to 9)
- underscore symbol (_)
By mistake, if we are using any other symbol like $ then we will get a syntax error.
- cash = 10 Correct statement
- ca$h =20 Incorrect Statement
2. Identifier should not start with digit,
- 123total Incorrect Statement
- total123 Correct statement
3. Identifiers are case-sensitive. Of course, Python language is case sensitive language.
- print (total) # Prints10
- print (TOTAL) #Prints 999
1. Alphabet Symbols (Either Upper case OR Lower case). That is (A to Z or a to z)
2. If the Identifier is started with Underscore (_) then it indicates it is private.
3. The identifier should not start with Digits. But identifier may contain digits except for the first character.
4. Identifiers are case-sensitive. Example total and Total are two different identifiers.
5. We cannot use reserved words as identifiers. Eg: def=10 or if = 20 or print = “Hello World”
6. There is no length limit for Python identifiers. But not recommended to use too lengthy identifiers.
7. Dollar ($) Symbol is not allowed in Python, that is $ symbol should not be a part of python identifier.
Test your Understanding
Q. Which of the following are valid Python identifiers?
Answer: Correct statements are — 2, 3, 5 as they follow the rules, set for defining identifiers.
Incorrect Statements are — 1 here identifier starts with digits, 4 here identifier has a special character that is $, 6 and 7 here both def and if are keywords.
If identifier starts with _ (Underscore) symbol then it indicates that it is private
If the identifier starts with two underscore symbols ie _ _, which indicates that the identifier is strongly private.
Finally, if the identifier both starts and ends with two underscore symbols, which indicates that the identifier is a language-defined special name. Eg: __add__ , __init__ and __str__
In this tutorial, you have learned the definition of Identifiers in Python Programs, The rules to define identifiers, and examples for valid and invalid identifiers.
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