How are variables created in Python? using pointers in Python

We have all studied the C Programming language and understand the ideas behind pointers. However is a quick recap.

Let us declare 2 variables in some program. The code would be

int a=3,b=4;

These 2 variables will get stored somewhere in memory.

Variable Name                Value                    Address  

a                                                                3                                        1000

b                                                                4                                        1002

C has 2 operators * and &. * is the value operator and gives the value at an address while & gives the address of a variable.

Let us declare two pointers now.

int *p1=&a,*p2=&b;

p1 = 1000 and p2=1002

*p1=3 and *p2=4

The equivalent statements in Python would be like this.

Program Sample

import _ctypes as ct
a,b=3,4
print(a,b)
p1,p2=id(a),id(b)
print(p1,p2)
print(ct.PyObj_FromPtr(p1),ct.PyObj_FromPtr(p2))

All variables are stored in the dir list. There is a collection of global variables and a collection of local variables i,e variables in a function 

Here is a program that accesses it

a,b=3,4
variables =dir()
print("Dir ",variables)
for variable in variables:
    print(variable)
globalvariables=globals()
print("Global Variables")
for variable in globalvariables:
    print(variable)
def f():
    print("Local Variables")
    la=2
    lb=3
    localvariables=locals()
    for variable in localvariables:
        print(variable)

f()

Output

Dir  ['__annotations__', '__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__', 'a', 'b']

__annotations__

__builtins__

__cached__

__doc__

__file__

__loader__

__name__

__package__

__spec__

a

b

Global Variables

__name__

__doc__

__package__

__loader__

__spec__

__annotations__

__builtins__

__file__

__cached__

a

b

variables

variable

globalvariables

Local Variables

lb

la

All variables are available in the dictionary returned by vars().

Program Sample

import IPython as ip
a,b=1,2
variables=vars()
print(variables)
print(type(variables))
print(variables.keys())
print(variables.values())
variables.pop("a")
print(variables.keys())

 

{'__name__': '__main__', '__doc__': None, '__package__': None, '__loader__': <_frozen_importlib_external.SourceFileLoader object at 0x000000CFCB62C160>, '__spec__': None, '__annotations__': {}, '__builtins__': <module 'builtins' (built-in)>, '__file__': 'C:/Users/Champak Roy/PycharmProjects/pythonProject3/chapter 2.py', '__cached__': None, 'ip': <module 'IPython' from 'H:\\Anaconda3\\lib\\site-packages\\IPython\\__init__.py'>, 'a': 1, 'b': 2, 'variables': {...}}
<class 'dict'>
dict_keys(['__name__', '__doc__', '__package__', '__loader__', '__spec__', '__annotations__', '__builtins__', '__file__', '__cached__', 'ip', 'a', 'b', 'variables'])
dict_values(['__main__', None, None, <_frozen_importlib_external.SourceFileLoader object at 0x000000CFCB62C160>, None, {}, <module 'builtins' (built-in)>, 'C:/Users/Champak Roy/PycharmProjects/pythonProject3/chapter 2.py', None, <module 'IPython' from 'H:\\Anaconda3\\lib\\site-packages\\IPython\\__init__.py'>, 1, 2, {'__name__': '__main__', '__doc__': None, '__package__': None, '__loader__': <_frozen_importlib_external.SourceFileLoader object at 0x000000CFCB62C160>, '__spec__': None, '__annotations__': {}, '__builtins__': <module 'builtins' (built-in)>, '__file__': 'C:/Users/Champak Roy/PycharmProjects/pythonProject3/chapter 2.py', '__cached__': None, 'ip': <module 'IPython' from 'H:\\Anaconda3\\lib\\site-packages\\IPython\\__init__.py'>, 'a': 1, 'b': 2, 'variables': {...}}])
dict_keys(['__name__', '__doc__', '__package__', '__loader__', '__spec__', '__annotations__', '__builtins__', '__file__', '__cached__', 'ip', 'b', 'variables'])