Variable and Value
- A variable is a memory location where a programmer can store a value. Example : roll_no, amount, name etc.
- Value is either string, numeric etc. Example : “Sara”, 120, 25.36
- Variables are created when first assigned.
- Variables must be assigned before being referenced.
- The value stored in a variable can be accessed or updated later.
- No declaration required
- The type (string, int, float etc.) of the variable is determined by Python
- The interpreter allocates memory on the basis of the data type of a variable.
Python Variable Name Rules
- Must begin with a letter (a – z, A – B) or underscore (_)
- Other characters can be letters, numbers or _
- Case Sensitive
- Can be any (reasonable) length
- There are some reserved words which you cannot use as a variable name because Python uses them for other things.
Good Variable Name
- Choose meaningful name instead of short name. roll_no is better than rn.
- Maintain the length of a variable name. Roll_no_of_a-student is too long?
- Be consistent; roll_no or or RollNo
- Begin a variable name with an underscore(_) character for a special case.
Variable assignment
We use the assignment operator (=) to assign values to a variable. Any type of value can be assigned to any valid variable.
a = 5
b = 3.2
c = "Hello"Here, we have three assignment statements. 5 is an integer assigned to the variable a.
Similarly, 3.2 is a floating point number and "Hello" is a string (sequence of characters) assigned to the variables b and c respectively.
Multiple assignments
In Python, multiple assignments can be made in a single statement as follows:
a, b, c = 5, 3.2, "Hello"If we want to assign the same value to multiple variables at once, we can do this as
x = y = z = "same"This assigns the “same” string to all the three variables.