DEV Community: Vidit Sarkar

Python Basics (Working with Interpreter and writing code in file)

Vidit Sarkar — Mon, 16 Mar 2020 13:15:59 +0000

Introduction

In my previous post I have discussed about how to install Python in your system. In this post I will go through how to work with Python Interpreter and how to write python code in a file and run it.

Working with Python interpreter
Writing code in a file and run it
What code editor should I use?

Working with Python interpreter

In your terminal type python and hit enter. You will see something like this

\> python
Python 3.7.4 (default, Aug  9 2019, 18:34:13) [MSC v.1915 64 bit (AMD64)] :: Anaconda, Inc. on win32
Type "help", "copyright", "credits" or "license" for more information.
>>>

>>> sign is a indication that you are in python shell. Now type 3+2 and hit enter. Output will be 5,

>>> 3+2
5
>>>

You can also use -, * or / for subtraction, multiplication and division respectively.

Let us write a simple for-loop (I will discuss more about for-loop in a later post).

>>> for i in range(4):
...     print(i)
...
0
1
2
3
>>>

If you are typing something which will take multiple lines then those ... signs will going to show up. They are indication of continuation lines. Notice there is a colon after range statement and 4 spaces before print statement. That : sign is necessary (you can refer to here for more info). You can use any number of spaces, but they have to be greater than zero. It is a good practice to use 4 spaces, so I am going to use 4 spaces.

Writing code in a file and run it

Interpreter is good for small code and for testing purposes. But if your code gets bigger, then you should consider using a file. One main benefit is that you can save and use it for later purposes, but the code in interpreter can not be saved using easy methods (At least I think so).Here are the steps,

Create a file with .py extension and avoid using spaces in the name. Example - app.py.
Copy and paste the code of for-loop in that file and save it. Same rule for spaces are also applicable here and also don't forget to put the : sign.

for i in range(4):
    print(i)

In the terminal type python app.py and you will see output like this.

\> python app.py
0
1
2
3

\>

By default, Python source files are treated as encoded in UTF-8. To declare an encoding other than the default one, a special comment line should be added as the first line of the file. The syntax is as follows,

# -*- coding: encoding -*-

For example, to declare that Windows-1252 encoding is to be used, the first line of your source code file should be,

# -*- coding: cp1252 -*-

You can check more about valid encodings here. Note that # sign indicates a comment line in python.
One exception to the first line rule is when the source code starts with a UNIX “shebang” line (not for Windows users). In that case, the encoding declaration should be added as the second line of the file.

#!/usr/bin/env python3
# -*- coding: ascii -*-

On BSD’ish Unix systems, Python scripts can be made directly executable, like shell scripts, by putting the line,

#!/usr/bin/env python3

at the very beginning of the file (assuming that the interpreter is on the user’s PATH). #! must be the first two characters of the file.

Give the script executable mode, or permission, using chmod and run it like a script.

$ chmod +x app.py

You can check more about this here.

What code editor should I use?

There are lots of popular code editors available out there like Visual Studio Code, Atom, Notepad++ and more. You can use any editor you prefer. You can even use IDEs. As long as you can write code and run it, any code editor or IDE should be fine. I personally use Visual Studio Code or Notepad++ to write code and run python files using command prompt (or integrated terminal of VS Code).

Happy coding!

Python Basics (Installation)

Vidit Sarkar — Mon, 16 Mar 2020 10:16:21 +0000

Introduction

Python is an interpreted, high-level, general-purpose programming language. It has variety of use cases. You can use it for automating certain tasks and do a lot more with it. Here we will see how to install python in your computer. By the way, we are going to use Python 3 not Python 2, so wherever I mention python that will mean Python 3, if not explicitly mentioned something else.

How to install Python
Other options
What I use
Hello World program

How to install Python

For Windows users

Check whether you have python in your system or not, by typing python in terminal or command prompt. If you see something like this, then you don't have python installed.

> python
'python' is not recognized as an internal or external command, operable program or batch file.

Head over to Python Official Website and go to the downloads section. Choose the latest stable python 3 version, download the executable file and install it. Do not forget to add python to your path, so that you can use python from terminal.

Make sure that the box, indicated using red arrow sign, is checked.

For Linux users

You should already have python in your system. You can verify it by typing python3 in terminal and then hitting enter. You should see something like this

$ python3
Python 3.6.9 (default, Nov  7 2019, 10:44:02)
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>

For Mac users

You should have python 2 in your system. To install python 3, you may need to use Homebrew. You can check out Python official site for more information.

Other options

Other popular options include Anaconda, ActiveState Python and more.

What I use

I personally use Anaconda Python. It comes with its own package manager, called conda and it has has lots of packages pre-installed, so you don't have to install them separately. Head over to their download page and download the version suitable for you system.

Check out their official installation guides.

For Windows users

You may need to add Anaconda to your path to use it from terminal. To do that, make sure the box, indicated using red arrow sign, is checked.

After the installation is successful, open a new terminal or command prompt and type python. You should see something like this

> python
Python 3.7.4 (default, Aug  9 2019, 18:34:13) [MSC v.1915 64 bit (AMD64)] :: Anaconda, Inc. on win32
Type "help", "copyright", "credits" or "license" for more information.
>>>

Hello World program

In the python shell after the >>> sign type print("Hello World") and hit enter. You will see output like this

> python
Python 3.7.4 (default, Aug  9 2019, 18:34:13) [MSC v.1915 64 bit (AMD64)] :: Anaconda, Inc. on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> print("Hello World")
Hello World
>>>

This is your Hello world program in python. Congratulations!

This is my first post!

DEV Community: Vidit Sarkar

Python Basics (Working with Interpreter and writing code in file)

Introduction

Contents

Working with Python interpreter

Writing code in a file and run it

What code editor should I use?

Python Basics (Installation)

Introduction

Contents

How to install Python

For Windows users

For Linux users

For Mac users

Other options

What I use

For Windows users

Hello World program