Which variable name is valid in Python?

Variable Names in Python: What Works and What Doesn’t

What are Variable Names?

In programming, a variable name is a string that represents a name given to a value. It is a crucial part of the programming language, and it has several important characteristics. In Python, variable names can contain letters, digits, and underscores. However, there are some rules and restrictions that govern the valid and invalid variable names.

Which Variable Names are Valid in Python?

Here is a list of valid variable names in Python:

• A-z, a-z, 0-9, and _ can be used as variable names
• **Characters that are not letters or digits, and special characters, can be used as variable names
• Special variable names:

  • True, False, and None
  • True, False, and None can be used as constant values
  • True, False, and None can be used as variable names (to the extent of 3 characters)

Here is a sample Python code:

print("Hello")  # This is a valid variable name

x = 5

print(x)  # This is a valid variable name

y = True  # This is a valid variable name

Which Variable Names are Not Valid in Python?

Here is a list of invalid variable names in Python:

• Variable names cannot start with a number
• Variable names cannot be empty
• Variable names cannot be all uppercase or all lowercase
• **Variable names cannot contain any special characters (except _)
• **Variable names cannot contain any word characters (except _)
• Variable names cannot contain any punctuation

Here is a sample Python code that shows why variable names are not valid:

print("Number")  # Error: variable name cannot start with a number

x = ""  # Error: variable name cannot be empty

y = "Hello"  # Error: variable name cannot be all uppercase or all lowercase

What About Symbols?

In Python, symbols such as !, @, #, $, etc. can be used as variable names. However, they cannot contain any special characters or words characters.

Here is a sample Python code that uses symbols as variable names:

print("!@#$")  # This is a valid variable name

What About Built-in Names?

Python has several built-in names that are not variable names, such as len(), max(), min(), sum(), etc. These names are not allowed as variable names.

Here is a sample Python code that shows why built-in names are not allowed as variable names:

print(len())  # Error: variable name cannot contain built-in names

Conclusion

In conclusion, variable names in Python are valid or invalid depending on the context in which they are used. Here is a summary of the rules and restrictions:

• Valid variable names: letters, digits, underscores, and special characters that are not built-in names
• Invalid variable names: variable names that start with a number, are empty, all uppercase or all lowercase, contain any special characters or words characters, or contain any built-in names

By following these rules and guidelines, you can write clear and readable Python code that is free from invalid variable names.