REPL (Read-Eval-Print-Loop)

It is an interactive development ene. It is a useful tool for experimentation and quick-testing. In REPL what ever we type in python will read, evaluate it , print the result and loop back to the beginning

Video

# Start REPL Starting REPL ## Windows Go to windows power shell or command prompt and type **python** ![Command Prompt](cmd-prompt-python.png) ## Linux In the bash shell type **python3** to start repel ```bash Python 3.5.2 vagrant@python-m1:~$ python3 Python 3.5.2 (default, Nov 17 2016, 17:05:23) [GCC 5.4.0 20160609] on linux Type "help", "copyright", "credits" or "license" for more information. >>> 
# Performe simple opreation
Type in the expression 1+2 and it is evalulated and result is printed.
![Simple Addition](repel-simple-add.png)
# Undrerscore in REPEL
Within the REPL, you can use the special underscore variable to refer to the most recently printed value.
```bash
vagrant@python-m1:~$ python3                                                        
Python 3.5.2 (default, Nov 17 2016, 17:05:23)                                       
[GCC 5.4.0 20160609] on linux                                                       
Type "help", "copyright", "credits" or "license" for more information.              
>>> x=2                                                                             
>>> x                                                                               
2                                                                                   
>>> _ * 3                                                                           
6                                                                                   
>>>

Notice _ contains previously printed value 2

Note: The underscore doesn't have any special behavior in Python scripts or program

Stop REPL

Sending End of file control character will exit the REPEL. Unfortunately, the means of sending this character varies across platforms

Windows

Ctrl+Z and Enter Stop REPL

Linux

Ctrl+D will exit the REPL environment

vagrant@python-m1:~$ python3                                            
Python 3.5.2 (default, Nov 17 2016, 17:05:23)                           
[GCC 5.4.0 20160609] on linux                                           
Type "help", "copyright", "credits" or "license" for more information.  
>>> 1+2                                                                 
3                                                                       
>>>                                                                     
vagrant@python-m1:~$

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