DEV Community: मौसम अधिकरी

Virtual Environment For My First Python Program

मौसम अधिकरी — Sat, 21 Mar 2020 11:27:28 +0000

Here We will create a virtual environment and code inside the environment.
So why virtual Environment?

to separate and isolate the packages we are using for different programs and projects.
working with code that depends on different versions of some library.
This issue happens a lot when dealing with Python 2 and Python 3.
Having different versions of packages installed can lead to a lot of confusion and bugs.

It’s much better to have separate environments for separate programs.

The module we use to create virtual environment here is called venv.

venv will install most recent version of python that is available.

To create a virtual environment, We have to decide upon a directory where we want to place it. And run venv module as script with directory path.

Suppose we want to create a virtual environment at home/dev:
then change directory to the path as follows
```
 $cd home/dev
```

Now inside the directory we will run venv script:

     ~/dev$ python -m venv python-dev

What this does is:

creates python-dev directory if it doesn't exist
also creates directories inside it containing a copy of the python interpreter, the standard library and various supporting files.

Once we have created Virtual Environment, We have to activate it.

Run following command
On Windows:
```
 python-dev\scripts\activate
```
Here, extension for activate file should be mentioned whether its .bat for cmd or .ps1 for Power shell.
In cmd,
```
 Scripts\activate.bat
```

and in PowerShell,

     Scripts\Activate.ps1

Updated through comment
on Linux or Mac:

     source python-dev/bin/activate

After activating, we can start programming.
now create main.py file.

if you have vs code installed then you can simply type code main.py in your terminal.
```
 ~/dev/python-dev $ code main.py
```

This opens a main.py file in vscode editor.
Now we can code our first Python Program Here.

     def main():
         print("hello world!")
     if __name__=="__main__":
         main() 
     else:
         print("file invoked")

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Functions in Python

मौसम अधिकरी — Sat, 21 Mar 2020 11:18:50 +0000

What is function?

Function is way of problem solving by dividing the problem into sub-problems and finding their individual solution and combining them to solve original problem.

Function Definition:

defining the role of function
actions to be performed by functions are written in the form of statements here.

syntax:

    def function_name(parameters_seperated_by_commas):
        statements

notice the : and indentation i.e four white spaces.

Some Rules:

function_name must not be python keyword
code following colon(:) must be indented.

Function Call:

calling the defined function
to execute the work we need to call the defined function.
to execute function, We need to invoke function.
```
 function_name(arguments_seperated_by_commas)
```

Suppose we want to write a program that draws a house, a car and a cat.
Without use of function we end up writing whole code for drawing house, a car and a cat at a place.

     def main():
         statements for drawing house
         statements for drawing car
         statements for drawing cat

which works fine but tracking, debugging is difficult and probably not the best practice.
so what we do here is make function for individual work like:

     def draw_house():
         statements

     def draw_car():
         statements

     def draw_cat():
         statements

and we will call the defined function in our main function as:

     def main():

         draw_house()

         draw_car()

         draw_cat()

         print("task completed")

Types of Functions:

Void Functions:
- The function that doesn't return anything.
- simply speaking, The return type is None
  for example:
  If we want to add two numbers given to function and print it's result then:
```
def addition(num1,num2):
    print(f"{num1}+{num2}=",num1+num2)
```
Fruitful Functions:
- The function that returns some value
- The return type is not null.
  for example:
```
def addition(num1,num2):
    return num1+num2
```

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Setting Up Environment For Python

मौसम अधिकरी — Fri, 20 Mar 2020 18:23:54 +0000

Before Installing any software on your device consider the following

Whether your System is 32-bit or 64-bit
Which OS you are Using Mac/Linux/Windows
Memory space

Python is Pre-installed in Linux and Mac.

To open python shell:

open Terminal
Type Python
you will see

Now Type the following there:
```
>>>print("hello World!")
hello World!
```
If you want to have python3 but getting python2.7 instead then run this in your bash shell
```
$ echo "alias python=/usr/local/bin/python3" >> ~/.bashrc
```

what this does is this points python3,when python is called instead of python2.7.

For Windows

Download Python installation file from Python.org
After starting the installer, one of two options may be selected:

If you select “Install Now”:
- Python will be installed into your user directory
- The standard library, test suite, launcher and pip will be installed
- If selected, the install directory will be added to your PATH.
On selecting Install Now, the setup process begins and wait for the installation to complete.

Once the installation completes, choose Close.

P.S. By selecting ‘Add Python 3.X to PATH’ will save some troublesome of adding PATH to your system variables.

Since you can't do all the stuffs in console so we need an Editor.
I use VS Code
but there are many different editors out there of your choice. like Sublime text , Atom , Pycharm and so on

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Introducing Python

मौसम अधिकरी — Fri, 20 Mar 2020 16:57:09 +0000

Introducing Python:

Python is High level interpreted language.

Python is:

easy to learn
interactive programming language
efficient high level data structures
simple but effective approach to Object Oriented Programming.

Python's elegant syntax and dynamic typing together with it's interpreted nature ,makes python an ideal language for scripting and rapid application development in many areas on most platforms.

Python was developed by Guido Van Rossum in 1991 at the National Research institute for mathematics and computer science in Netherlands.

Naming of python was inspired from his favorite comedy show Monty's Python's Flying Circus.

Features Of Python:

Easy To learn and Use
Expressive language i.e more understandable and more readable
Interpreted language
Cross platform language
Free and Open-source
Object Oriented Language
Extensible language - C , C++ can be used to compile code
Large Standard Library
GUI programming Support

Applications of Python:

Web applications like Django , Pyramid , Flask
Desktop GUI applications using Tk , Wxwigets , kivi , PYQt
Software Development for build ,control ,management and testing etc
Scientific and Numeric applications like Scipy , Pandas , Numpy
Business Application like ERP, E-commerce as Tryton
Console Based Application like Ipython
Audio-Video based Application like Timeplayer , Cplay
3D CAD Applications like Fandango
Enterprise Application like OpenERP , Tryton , Picalo
Application for Images like Vpython , Gogh , Imgseek.

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