Variables and Data Types

What's Variable

Variables are containers for storing data values.

Python has no command for declaring a variable.

A variable is created the moment you first assign a value to it.

Variables do not need to be declared with any particular type, and can even change type after they have been set.

Types are only associated with objects of variables

Variable Types

Strings

# define variable
name = "Ayman"
print(name)        
Output: Ayman

# new line
name = "Ayman\nAyman" 
print(name)        
Output: Ayman
          Ayman

# print \n in output -raw string-
name = r'Ayman\nAyman'  
print(name)        
Output: Ayman\nAyman

# unicode string
name = u'Ayman'
# convert unicode to string  
str(name)
# convert string to unicode
unicode(name) 

# add formating
name="""
Ayman
        Ayman
"""
print(name)
Output:
Ayman
	Ayman

Numbers

x = 1    # int
y = 2.8  # float
z = 1j   # complex

Operation on Variables

String Operations

• Strings are immutable

• Concatenation var1 + var2 = 'var1var2' var1 + '' +var2 = 'var1 var2'

• Repeated sequence buffer = "A"*100

• Slicing string[start:end:step]

• int to string int("100") Output: 100

• string.find(value)

• string.replace(old_value, new_value)

• and a lot more ... check manual

Numbers Operations

normal as other languages

x**y (x power y)

String Formatting

Option #1: %-formatting

name = "Ayman"
age = 22
print("Hello, %s." % name)
Output: 'Hello, Ayman.'
print("Hello, %s. You are %s." % (name, age))
Output: 'Hello Ayman. You are 22.'

Option #2: str.format()

name = "Ayman"
age = 22
print("Hello, {}. You are {}.".format(name, age))
Output: 'Hello, Ayman. You are 22.'
print("Hello, {1}. You are {0}.".format(age, name))
Output: 'Hello, Ayman. You are 22.'

Memory Location

x = 10
id(x)                  # Output: 9789280
hex(id(x))             # Output: '0x955f60'
name.__repr__          # Output: <method-wrapper '__repr__' of int object at 0x955f60>

Casting

If you want to specify the data type of a variable, this can be done with casting.

x = str(10)    # x will be '10'
y = int(10)    # y will be 10
z = float(10)  # z will be 10.0

Get the Type

You can get the data type of a variable with the type() function.

x = 10
y = "Ayman"        
print(type(x))        # <class 'int'>
print(type(y))        # <class 'str'>

Single and Double Quotes

both are the same

Case-Sensitive

Variable names are case-sensitive.