Internal working In Python - ProLearner00

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 INTERNAL WORKING IN PYTHON

Before you start working in Python, you need to install Python on your computers. There are multiple Python distributions available today. ◆ Default installation available from www.python.org is called CPython installation and
 
comes with Python interpreter, Python IDLE (Python GUI) and Pip (package installer). There are many other Python distributions available these days. Anaconda Python distribution is one such highly recommended distribution that comes preloaded with
 
many packages and libraries (e.g., NumPy, SciPy, Panda libraries etc.).
 
Many popular IDEs are also available e.g., Spyder IDE, PytCharm IDE etc. Of these, Spyder IDE is already available as a part of Anaconda Python distribution.
 
To install any of these distributions, PLEASE REFER TO APPENDIX A. We shall learn to work with both these distribution types [but my personal favourite is Anaconda ;) - not the reptile, the Python distribution :)]
 
Once you have Python installed on your computers, you are ready to work on it. You can work
 
in Python in following different ways:
 
(i)   in Interactive mode (also called Immediate Mode) (ii) in Script mode
 
Working in Default CPython Distribution


The default distribution, CPython, comes with Python interpreter, Python IDLE (GUI based) and pip (package installer). To work in interactive as well as script mode, you need to open Python IDLE.
 

Working in Interactive Mode (Python IDLE)

Interactive mode of working means you type the command - one command at a time, and the Python executes the given command there and then and gives you output. In interactive mode, you type the command in front of Python command prompt >>>. For example, if you type 2 +5 in front of Python prompt, it will give you result as 7:
 
Result returned by Python
 
>>>2+5← command/expression given here 7
 
To work in interactive mode, follow the process given below: (i) Click Start button → All Programs Python 3.6.x→ IDLE (Python GUI) [see Fig. 1.1(a)] ->>
 
Or
 
Click Start button → all Programs → Python 3.6.x → Python (command line)
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(ii) It will open Python Shell [see Fig. 1.1(b)] where you'll see the Python prompt (three signs ie., >>>).

python

(iii) Type commands in front of this Python prompt and Python will immediately give you the result. [see Fig. 1.1(c)]

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 For example, to print string "Hello" on the screen, you need to type the following in front of Python prompt (>>>)

>>> print ("Hello")
And Python interpreter will immediately display string Hello below the command. To display, you just need to mention name or expression [Fig. 1.1(c)] in front of the prompt.
 
Figure 1.1(c) shows you some sample commands that we typed in Python shell and the output returned by Python interpreter.
 

Working in Script Mode (Python IDLE)

Interactive mode proves very useful for testing code: you type the commands one by one and get the result or error one by one.
What if you want to save all the commands in the form of program file and want to see all output lines together rather than sandwiched between successive commands? With interactive mode, you cannot do so, for:
 
Interactive mode does not save the commands entered by you in the form of a program. The output is sandwiched between the command lines [see Fig. 1.1(c)].
The solution to above problems is the Script mode. To work in a script mode, you need to do the following:
 
Step 1: Create Module / Script / Program File
 
Firstly, you have to create and save a module / Script / Program file.
 
To do so, follow these instructions:
 
(i) Click Start button All Programs → Python 3.6.x→ IDLE. [Fig. (ii) Click File → New in IDLE Python Shell. [Fig. 1.2(a)]
 
1.2(a)]
 
(iii) In the New window that opens, type the commands you want to save in the form of a program (or script).
[Fig. 1.2(b)]
 
For instance, for the simple Hello World program, you'll need to type following line :
 
print ("Hello World!")



(iv) Click File → Save and then save the file with an extension .py. The Python programs has .py extension [Fig. 1.2(c)]. For instance, we gave the name to our program as
 
Hello.py.
 
Now your program would be saved on the disk and the saved file will have .py extension.
 
Step 2: Run Module / Script / Program File
 
After the program/script file is created, you can run it by following the given instructions:
 
(i) Open the desired program/script file that you created in previous Step 1 by using IDLE's File→→ Open command. If the program / script file is already open, you can directly move to next instruction.
 
(ii) Click Run → Run Module command [Fig. 1.3(a)] in the open program / script file's window.
 
You may also press F5 key.

(ii) And it will execute all the commands stored in module / program / script that you had opened and show you the complete output in a separate Python Shell window. [Fig. 1.3(b)]
 



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