Define variable in Python
Literal
A literal is a number or string that appears directly in a program.
The following are all literals in Python:
42 # Integer literal
3.14 # Floating-point literal
1.0j # Imaginary literal
'hello' # String literal
"world" # Another string literal
"""Good night""" # Triple-quoted string literal
# w ww . j av a 2s .c o m
Using literals and delimiters, you can create data values of some other fundamental types:
[ 42, 3.14, 'hello' ] # List
( 100, 200, 300 ) # Tuple
{ 'x':42, 'y':3.14 } # Dictionary
Define variables
A variable is basically a name that represents some value.
You have to assign a value to a variable before you use it.
x = 3
print x * 2
The code above generates the following result.
Once a variable has been assigned, you can access it by using its name.
x = 4
y = 'this is a string'
print x
print y
The code above generates the following result.
Chained Assignments
x = y = 2
print x
print y
The code above generates the following result.
Augmented Assignments
x = 2
x += 1
x *= 2
print x
The code above generates the following result.
Sequence Unpacking
x, y, z = 1, 2, 3
print x, y, z
x, y = y, x
print x, y, z
The code above generates the following result.
Dynamically typed
Python is dynamically typed, no pre-declaration of a variable or its type is necessary.
The type and value are initialized on assignment. Assignments are performed using the equal sign.
counter = 0# from w w w. j av a2s . c o m
miles = 1000.0
name = 'Bob'
counter = counter + 1
kilometers = 1.609 * miles
print '%f miles is the same as %f km' % (miles, kilometers)
The code above generates the following result.
None placeholder
X = None # None placeholder
print X # w w w . j a v a 2s .co m
L = [None] * 100 # Initialize a list of 100 Nones
print L
print type(L) # Types
print type(type(L)) # Even types are objects
The code above generates the following result.
