''' Purpose: look under hood about variables, values, objects, types, and identity
'''

# define three variables 

x = 11
y = '11'
z = 11.0

print( 'What are the values of the variables?' )
print( 'x =', x )
print( 'y =', y )
print( 'z =', z )

print() ; input( 'Enter when ready: ' ); print()

#####################################################################

# Python stores values internally as objects (digital information objects)

# Python keeps track of the type of value that an object hold

# Python has a built-in function type() to find out the type of value 
# held by an object

x_type = type( x )
y_type = type( y )
z_type = type( z )

print( 'What type of objects do the variables hold?' )
print( '    x holds a', x_type )
print( '    y holds a:', y_type )
print( '    z holds a:', z_type )

print() ; input( 'Enter when ready: ' ); print()

#####################################################################

# The value of a Python variable is an indicator where in memory to find
# its associated object.  The indicator is called in Python its id.  
# Programmers commonly refer to an id as an address or reference.

# Every Python object has a unique id.  The id can be found out with
# built-in function id().  

x_id = id( x )
y_id = id( y )
z_id = id( z )

print( 'What are the ids of the variables?' )
print( '    x id is', x_id )
print( '    y id is', y_id )
print( '    z id is', z_id )

print() ; input( 'Enter when ready: ' ); print()

#####################################################################

# Variables can indicate (reference) the same object.

a = 11
b = 11

a_id = id( a )
b_id = id( b )

print( 'Can variables indicate the same object; i.e., can they reference the same object?' )
print( '    variable a has value', a, 'and id', a_id )
print( '    variable b has value', b, 'and id', b_id )

print() ; input( 'Enter when ready: ' ); print()

#####################################################################

# Objects can have different occurrences of the same value. If they do their id's will be distinct

a = '11'
b = str( 11 )

a_type = type( a )
b_type = type( b )

a_id = id( a )
b_id = id( b )

print( 'Can objects have the same value?' )
print( '    Variable a references value', a, 'of type', a_type, 'with id', a_id )
print( '    Variable b references value', b, 'of type', b_type, 'with id', b_id )

print(); input( 'Enter when ready: ' ); print()

#####################################################################

# The value of a variable can change during a program.  If so, its id changes

a = 11
a_id = id( a )

print( 'Can variables change their values? ' )
print( '    Variable a references value', a, 'with id', a_id )

a = 12
a_id = id( a )
print( '    Variable a references value', a, 'with id', a_id )

print()