Python - Basics

Prerequisite

Installing python and launching the interactive shell.

Math Operators from Highest to lowest precedence (Order of operations) 


| Operator     | Operation           | Example     | Evaluates to |
|--------------|---------------------|-------------|--------------|
| **           | Exponent            | 2**3        | 8            |
| %            | Modulo              | 22%8        | 6            |
| //           | Integer Division    | 22//8       | 2            |
| /            | Divison             | 22/8        | 2.75         |
| *            | Multiplication      | 3*5         | 15           |
| -            | Substraction        | 5-2         | 3            |
| +            | Addition            | 2+2         | 4            |


You can always test to see whether an instruction works by typing it into the interactive shell. Don’t worry about breaking the computer : The worst thing that could happen is that Python responds with an error message.

Data Types

A data type is a category for values, and every value belongs to exactly one data type. The most common data types in Python are Integers, Floating-point numbers and Strings.

For the strings type, Python knows where it begin and ends with the single quote (‘’) surrounding the text, If you ever see the error message SyntaxError : EOL while scanning string literal, you probably forget the final single quote character at the end of the string.

String Concatenation and Replication

The meaning of an operator may change based on the data types of the values next to it. For example, + is the addition operator when it operates on two integers or floating-point values. However, when + is used on two string values, it joins the strings as the string concatenation operator.

But you can’t concatenate variables with different types. Python will display the error Can’t Convert ‘int’ object to str implicitly **Remember the Zen of Python; Explicit is better than Implicit** . So your code will have to explicitly convert the integer to a string because python can’t do this automatically. (We will discuss data types conversion later). The * operator is used for multiplication when it operates on two integers or floating-point values. But when the * operator is used on one string value and one integer value, it becomes the string replication operator.



The * operator can be used with only two numeric values (for multiplication) or one string value and one integer value (for string replication). Otherwise, Python will just display an error message.

Variables

Rules of naming variables in python :

  1. It can be only one word.
  2. It can use only letters, numbers, and the underscore ‘_’ charcter.
  3. It can’t begin with a number.
  4. Variable names are case-sensitive.

Some programmers use camelcase for variable names (LookLikeThis) instead of underscores (Look_Like_This).

Before we move on to next element, I want to mention that python does not support constants (Non-changing value assignments) like some other languages.

Python files

The interactive shell is cool, but now we need to write our code and save it into .py files. I will not get deeper into the text editors and OSs but I’m using Vim and Ubuntu distro so the next line commands are entered into a linux terminal, so basically this is the script of our first python program where we print some text and ask for a name and an age and then use them for a reply.

Enough for today, see you tomorrow ! <3 Stay Home, Stay Safe!