To create a variable in Python, all you need to do is specify the variable name, and then assign a value to it.
<variable name> = <value>
Python uses =
to assign values to variables. There’s no need to declare a variable in advance (or to assign a data type to it), assigning a value to a variable itself declares and initializes the variable with that value. There’s no way to declare a variable without assigning it an initial value.
# Integer
a = 2
print(a)
# Output: 2
# Integer
b = 9223372036854775807
print(b)
# Output: 9223372036854775807
# Floating point
pi = 3.14
print(pi)
# Output: 3.14
# String
c = 'A'
print(c)
# Output: A
# String
name = 'John Doe'
print(name)
# Output: John Doe
# Boolean
q = True
print(q)
# Output: True
# Empty value or null data type
x = None
print(x)
# Output: None
Variable assignment works from left to right. So the following will give you an syntax error.
0 = x
=> Output: SyntaxError: can't assign to literal
You can not use Python’s keywords as a valid variable name. You can see the list of keywords by:
import keyword
print(keyword.kwlist)
Rules for variable naming:
Variables names must start with a letter or an underscore.
x = True # valid
_y = True # valid
9x = False # starts with numeral
=> SyntaxError: invalid syntax
$y = False # starts with symbol
=> SyntaxError: invalid syntax
The remainder of your variable name may consist of letters, numbers and underscores.
has_0_in_it = “Still Valid”
Names are case sensitive.
x = 9
y = X*5
=>NameError: name 'X' is not defined
Even though there’s no need to specify a data type when declaring a variable in Python, while allocating the necessary area in memory for the variable, the Python interpreter automatically picks the most suitable built-in type for it:
a = 2
print(type(a))
# Output: <type 'int'>
b = 9223372036854775807
print(type(b))
# Output: <type 'int'>
pi = 3.14
print(type(pi))
# Output: <type 'float'>
c = 'A'
print(type(c))
# Output: <type 'str'>
name = 'John Doe'
print(type(name))
# Output: <type 'str'>
q = True
print(type(q))
# Output: <type 'bool'>
x = None
print(type(x))
# Output: <type 'NoneType'>
Now you know the basics of assignment, let’s get this subtlety about assignment in python out of the way.
When you use =
to do an assignment operation, what’s on the left of =
is a name for the object on the right. Finally, what =
does is assign the reference of the object on the right to the name on the left.
That is:
a_name = an_object # "a_name" is now a name for the reference to the object "an_object"
So, from many assignment examples above, if we pick pi = 3.14
, then pi
is a name (not the name, since an object can have multiple names) for the object 3.14
. If you don’t understand something below, come back to this point and read this again! Also, you can take a look at this for a better understanding.