Variable is a way to refer to memory locations being accessed by a computer program. In languages like C, C++, Java, a variable is a name given to a memory location. So when we say:

int x;
float y;

This small piece of code asks the compiler to create memory space for the variables, 4 bytes each (the size depends on the compiler and programming language). The variables are basically names assigned to the memory location, if the variable is defined for a particular data type then only declared type data can be stored in it. But in python, we do not need to declare a variable beforehand like int x, we can straightaway move to define the variable and start using it like x = 10. alt text

Now the point is, how does Python know what is the type of the variable and how to access it? In Python, data types (integer, list, string, functions, etc. ) are objects and every object has a unique id that is assigned to it, at the time of object creation. Variables are references (pointers) to these objects. What happens when we say :

x = 10
  • Python executes the right-hand side of the code
  • Identifies 10 to be an integer
  • Creates an object of Integer class
  • Assigns x to refer to the integer object 10 alt text

Now if we create new variable y which is equal to x, what do you think happens internally?


y now refers to the same object as x. alt text

How do we know that? It can be verified by checking the id of the object that these two variables x and y are pointing to.

id(y) == id(x)
# output

We can also print the id of the object

print(f"id of the object pointed by x:{id(x)}")
print(f"id of the object pointed by y:{id(y)}") 

# output
#your id value might be different from mine but the two ids printed must be the same
id of the object pointed by x:140733799282752 
id of the object pointed by y:140733799282752

Now, what if we assign a different value to y?


This will create another integer object with the value 40 and y will now refer to 40 instead of 10. alt text How to check Again, we will use id() to see the ids of the objects.

print(x) # outputs 10
print(y) # outputs 40
print(f"id of the object pointed by x:{id(x)}")
print(f"id of the object pointed by y:{id(y)}")  

# output
id of the object pointed by x:140733799282752
id of the object pointed by y:140733799283712

As we can see from above, the two ids are now different which means a new object with value 40 is created and y refers to that object now.

If we wish to assign some other value to variable x

x = "python"

# output

We will get an object id that is different from the id “140733799282752” printed by id(x) for integer object 10 previously.

So what happened to the integer object 10? The integer object 10 now remains unreferenced and can no longer be accessed. Python has a smart garbage collection system that looks out for objects that are no longer accessible and reclaims the memory so that it can be used for some other purpose. alt text One last question: What if we create two integer objects with the same value?

p = 100
q = 100

Before I answer this question. Let's check their ids:

print(f"id of the object pointed by x:{id(p)}")
print(f"id of the object pointed by y:{id(q)}") 
# output
id of object pointed by x:140733799285632
id of object pointed by y:140733799285632

So what python does is optimize memory allocation by creating a single integer object with value 100 and then points both the variables p and q towards it.

Let's check one more example-

m = 350
n = 350

print(f"id of object pointed by x:{id(m)}")
print(f"id of object pointed by y:{id(n)}") 

# output
id of the object pointed by x:1783572881872
id of the object pointed by y:1783572881936

To our surprise the ids of the integer object 300 referred to by m and n are different. What is going on here?? Python allocates memory for integers in the range [-5, 256] at startup, i.e., integer objects for these values are created and ids are assigned. This process is also known as integer caching. So whenever an integer is referenced in this range, python variables point to the cached value of that object. That is why the object id for integer object 100 referenced by p and q print the same ids. For integers outside the range [-5, 256], their objects are created as and when they are defined during program implementation. This is the reason why the ids for integer object 350 referenced by m and n are different. As mentioned earlier, variables point to the objects stored in memory. Hence variables are free to point to object of any type.

x = 10 # x points to an object of 'int' type
x = ["python", 20, "apple"] # x now points to an object of type 'list'
x = "python" # x now points to a string type object

I hope you enjoyed reading it. Feel free to suggest improvements to the article or any other topic that you would like to know more about.

Free Software

“Free” software “is software that can be used, studied, and modified,” copied, changed with little or no restriction, and which can be copied and redistributed in modified or unmodified form. Free software is available gratis (free of charge) in most cases. “In practice, for software to be distributed as free software, the human-readable form of the program (the source code) must be made available” along “ with a notice granting the” user permission to further adapt the code and continue its redistribution for free. This notice either grants a “free software license”, or releases the source code into the public domain.

Open-Source Software

In the beginning, all software was free in the 1960s, when IBM and others sold the first large-scale computers, these machines came with software which was free. This software could be freely shared among users, The software came written in a programming language (source code available), and it could be improved and modified. Manufacturers were happy that people were writing software that made their machines useful. Then proprietary software dominated the software landscape as manufacturers removed access to the source code. IBM and others realized that most users couldn’t or didn’t want to “fix” their own software and There was money to be made in leasing or licensing software. By the mid-1970s almost all software was proprietary “Proprietary software is software that is owned by an individual or a company (usually the one that developed it). There are almost always major restrictions on its use, and its source code is almost always kept secret.” users were not allowed to redistribute it, source code is not available users cannot modify the programs. Software is an additional product that was for sale In 1980 US copyright law was modified to include software In late 1970s and early 1980s, two different groups started what became known as the open-source software movement: East coast, Richard Stallman (1985), formerly a programmer at the MIT AI Lab, launched the GNU Project and the Free Software Foundation. “to satisfy the need for and give the benefit of ‘software freedom’ to computer users ultimate goal of the GNU Project was to build a free operating system the GNU General Public License (GPL) was designed to ensure that the software produced by GNU will remain free, and to promote the production of more and more free software.

I was thinking to note down my thoughts so that I can share my experience. So here it is, about how I joined 'dgplug' and get to know about Open-Source.

During my B.Tech 3rd semester somehow I got to know about the word 'Open-Source'. After a year when I was a fifth semester student, I met 'Ratnadeep(rtnpro)' in a tech-talk at my college,talk was over Open-Source , Its opportunities and freedom.Open Source culture was a myth in my college, very few people knew about Open-Source and its freedom of learning. In my batch, hardly fifty percent people know about Open-Source and Communities. During the talk 'Ratnadeep debnath(rtnpro)' mentioned about 'dgplug' summer training program and also told about 'Kushal das(kushal)' and other 'dgplug' operators, in those days I was learning python so after the talk a name was coming again and again in my mind that was 'Kushal das(kushal)', there were many questions and doubts were in my mind e.g. how to start, where to start then I decided to ping 'Ratnadeep debnath(rtnpro)' and he helped me a lot. I was a hindi background student till my 12th standard so I was a little bit shy to talk ans also I was a window user in those days then 'Ratnadeep debnath(rtnpro)' suggested me to shift over fedora, and also suggest to join IRC to get enrolled in 'dgplug' where masterminds like Kushal, Ratnadeep(rtnpro), Sayan, Chandan , Jasonbraganza were there. Summer training program had been started 15 days before i joined. 'Kushal das' suggested me to go through the logs, I did that. Kushal das(kushal) provided his book for python named 'Python you and me', book helped me a lot to understand python with a decent practice. I started digging more about Open-Source and i got my interests in it. At the beginning, after trying on my own, I lost hope because I was struggling to learn to contribute and thought that it's impossible ,I started staying on 'dgplug' after sessions and listened to people what they are taking and used to ask questions frequently whenever doubt appeared in my mind as time passed thing became easier, it's just start for me many thing to go. Jasonbraganza's sessions over reading and writing importance was amazing and encouraged me and many more to write, I am very much thankful to him for his kind help. That's how it all started for me.