The Python programming language

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Python is a general purpose programming language.

Python is powerful... and fast; plays well with others; runs everywhere; is friendly & easy to learn; is Open. From the Python web site at https://www.python.org/.

What is a python? A python is a snake.

The programming language Python comes from the British comedy group Monty Python

Python is a simple interpreted object-oriented programming language system that has extensive standard libraries that can be used for many types of practical programming. Python runs on many different platforms and has been ported to the Java and .NET virtual machines. It is distributed under an open source license that makes it free for even commercial products. The official Python web site is at http://www.python.org.

Python 1.0 was first released in 1991. It was conceived by Guido van Rossum.

Python 2.0 was released in 2000. The current version is 2.7. Support for Python 2.x is due to be discontinued in January 2020.

Python 3.0 was released in 2008. The current version is 3.7.

Python has a simple syntax that uses indentation rather than begin/end or curly braces.

Python provides extensive support for many functional programming capabilities.

Python 3.x provides better support for asynchronous, parallel, and concurrent programming.

There is an extensive library of functionality available (all versions).

The package manager is called pip.

Core philosophy (from Wikipedia):

Beautiful is better than ugly
Explicit is better than implicit
Simple is better than complex
Complex is better than complicated
Readability counts

From Wikipedia:

Python embraces a "there should be one—and preferably only one—obvious way to do it" design philosophy.

To describe something as 'clever' is not considered a compliment in the Python culture.

One often hears/reads the phrase: "Thy Pythonic way of doing it is ...".

In many programming languages (e.g., C, Java, etc.) there is more than one way to write an if statement.

// one way - curly braces if (b) { x+= 2; } // another way - no curly braces if (b) x += 2; // other ways - change indent on curly braces

Due to style considerations, one should not use the second form above (always do similar things in the same way).

Python only has one way so there is no choice.

if b: x += 2;

Note that the parentheses around the boolean expression b are not needed in Python.

The file type of a Python program file is py.

The following Linux command(s) create/edit a hello program in the your home directory using the nano text editor.

nano ~/hello.py

Create the following program text in the editor that will output the text "Hello world"

print("Hello world")

To exit with save, remember to press Ctrl-X, then "y" (for yes) and Enter to exit.

The following Linux command(s) run the program.

python ~/hello.py

The output should be as follows.

Hello world

Let us look at a program to implement to algorithm for decimal to binary conversion.

The routine toBinary1 takes as input a value and returns the string representation in binary (base 2)

The first part of the program will use the hard-coded value of 156.

The second part will use a loop to output the decimal values and binary representations of the values from 0 to 16.

Here is the Python code [#1]

def toBinary1(x1):
	s2 = ""
	if x1 == 0:
		s2 = "0"
	else:
		while x1 != 0:
			r1 = x1 % 2
			r1 = math.floor(r1)
			x1 = x1 // 2
			x1 = math.floor(x1)
			s2 = str(r1) + s2
	return s2
x1 = 156
s1 = toBinary1(x1)
print("Value {0:d}d in binary is {1:s}b.".format(x1,s1))
print("")
for i1 in range(0,16+1):
	s1 = toBinary1(i1)
	print("{0:d}d = {1:s}b".format(i1,s1))

Here is the output of the Python code.

For comparison, below is the above Python code example in Java.

Here is the Java code [#1]

public class dtob_01 {
	public String toBinary1(int x1) {
		String s2 = "";
		if (x1 == 0) {
			s2 = "0";
			}
		else {
			while (x1 != 0) {
				int r1 = x1 % 2;
				r1 = (int) (r1);
				x1 = x1 / 2;
				x1 = (int) (x1);
				s2 = r1 + s2;
				}
			}
		return s2;
		}
	public dtob_01() {
		int x1 = 156;
		String s1 = toBinary1(x1);
		System.out.print(String.format("Value %dd in binary is %sb.\n",x1,s1));
		System.out.print("\n");
		for (int i1=0; i1 <= 16; i1++) {
			s1 = toBinary1(i1);
			System.out.print(String.format("%dd = %sb\n",i1,s1));
			}
		}
	public static void main(String [] args) {
		new dtob_01();
		}
	}

Here is the output of the Java code.

Value 156d in binary is 10011100b.
0d = 0b
1d = 1b
2d = 10b
3d = 11b
4d = 100b
5d = 101b
6d = 110b
7d = 111b
8d = 1000b
9d = 1001b
10d = 1010b
11d = 1011b
12d = 1100b
13d = 1101b
14d = 1110b
15d = 1111b
16d = 10000b