Two days of learning the basics of Python

Introduction to a series of articles on Python basics in two days

The two-day Python basics series of articles is the python part of the "learn by example" programming course. The original English Github repository is clicked here, and all the content has been posted to the short book (see chapters).
This series is only for learning and reference. My ability is limited. Many professional terms are in the process of learning. Please correct me if you make a mistake.

brief introduction:

• installation
• Hello World example
• Python interpreter
• Python standard library

From Wikipedia

Python is a widely used high-level programming language, a general-purpose programming language, created by Guido Van Rossum, the first edition was released in 1991. It can be regarded as an improved LISP (adding some advantages of other programming languages, such as object-oriented). As an interpreted language, Python's design philosophy emphasizes code readability and concise syntax (especially the use of space indentation to divide code blocks instead of braces or keywords). Compared to C++ or Java, Python allows developers to express ideas with less code. Regardless of whether it is a small or large program, the language tries to make the structure of the program clear.

Guido van Rossum (Dutch: Guido van Rossum, January 31, 1956 -), born in Haarlem, the Netherlands, is a computer programmer, the original designer and main architect of the Python programming language. In the Python community, Guido Van Rossum is considered a "benevolent dictator" (BDFL), which means that he still pays attention to the Python development process and makes decisions when necessary.

Installation

• Get the Python suitable for your system from the official website-https://www.python.org/

• Most Linux distributions have Python installed by default

• See also this guide for more details and how to set up a virtual environment, how to use pip (never use sudo pip unless you know what you are doing).

• This example uses Unix-like system, Python version 3 and uses bash shell

• You can also run Python code online

• pythontutor-code executor for python 2 and python 3, visual code flow, with sample programs

• jupyter-a web application: allows you to create and share dynamic documents containing code, formulas, visualizations and explanations

• ideone-online compilation and debugging tool, allowing you to execute and compile more than 60 programming languages online

• Python Interpreter shell

• It is assumed that you are familiar with the command line. If not, check the basic tutorials and Linux integration resource list on ryanstutorials

Hello World example

Let's start learning to use Python from a simple program:

#! /usr/bin/python3

print("Hello World")

The first line has two parts

• /usr/bin/python3 is the path of the Python interpreter
• #! Called shebang, it specifies the interpreter that executes this script file.

The third line outputs the Hello World message, and the print function will add a newline after it by default.

Run Python program

You can use some text editors like gedit, vim or other editors to write script programs. After saving the file, add execute permission and run the program from the terminal.

$ chmod +x hello_world.py

$ ./hello_world.py
Hello World

Here is how to find the Python path and its version:

$ type python3
python3 is /usr/bin/python3

$ python3 --version
Python 3.4.3

If you have studied the Python 2 tutorial or have experience in Perl, it is easy to forget to add parentheses to the print function. This is a common mistake.

#! /usr/bin/python3

print "Have a nice day"

• Depending on the type of error, it may be very easy to locate the error location based on the information output by the execution program
• In this example, we get the appropriate "missing brackets" information

$ ./syntax_error.py
 File "./syntax_error.py", line 3
 print "Have a nice day"^
SyntaxError: Missing parentheses in call to 'print'

Single-line comments start at

#

• #! Only the first line of the program has a special meaning

In later chapters we will see multi-line comments

#! /usr/bin/python3

# Greeting message
print("Hello World")

Further reading

• Python Documentation-Version 3
• Different ways to execute Python programs
• Where is Python used?
• Python documentation-errors and exceptions
• Common grammatical errors

Python interpreter

• Usually used to execute a short paragraph of Python statements for the purpose of learning and debugging
• The prompt is >>>
• Some topics in the following chapters will use the Python interpreter for examples
• The special variable _ saves the result of the last output expression
• We can type only part of the command and repeatedly press the Up key to match historical commands
• The Ctrl+l key combination is used to clear the screen and save any typed commands intact
• exit()Exit

$ python3
Python 3.4.3(default, Oct 142015,20:28:29)[GCC 4.8.4] on linux
Type "help","copyright","credits" or "license"for more information.>>>print("hi")
hi
>>> abc
Traceback(most recent call last):
 File "<stdin>", line 1,in<module>
NameError: name 'abc' is not defined
>>> num =5>>> num
5>>>3+47>>>12+ _
19>>> exit()

Further reading

• Python documentation-using the Python interpreter
• Python documentation-interpreter example

Python Standard Library

• Python Documentation-Libraries
• pypi-Python programming language software repository

The library contains built-in modules (written in C)—providing system feature interfaces such as file I/O and modules written in Python—providing standard solutions for many schedule programming problems.

Some of these modules encourage and enhance the compatibility of Python programs by abstracting platform-specific functions into platform-compatible APIs.

         Editor: Wu Pancheng