Learn Python from Scratch - Introduction

Python is the language of the Python Interpreter and those who can converse with it. An individual who can speak Python is known as a Pythonista. It is a very uncommon skill, and nearly all known Pythonistas use software initially developed by Guido van Rossum.

When we are at the python interpreter, it displays chevron prompt (>>>) on the terminal, where it is asking you “What’s next??”.

How do we speak the language of python??

This must be the question on most of your minds when trying to learn the language initially. Just like the English Language, we will first start of by learning words, sentences and then paragraphs in python.

Reserved Words: They’re words that are predefined in the python library and have some meaning. These words cannot be used as variables or as a matter of fact to do anything that these words don’t offer. Some of these reserved words that we would come across are stated in the figure alongside.

Constants and variables are other literals that are supported by python. “Constants”, as the word suggests they’re fixed values such as numbers, letters, and strings, where their value does not change throughout the scope of the program. A variable is a named place in the memory where a programmer can store data and later retrieve the data using the variable “name”.

Since we programmers are given a choice in how we choose our variable names, there is a bit of “best practice”, we name variables to help us remember what we intend to store in them (“mnemonic” = “memory aid”). This can confuse beginning students because well-named variables often “sound” so good that they must be keywords. There are rules that have to be followed while naming a variable so as to reduce ambiguity for the interpreter, and they’re:

1.  Must start with a letter or underscore _
2. Must consist of letters, numbers, and underscores
3. Case Sensitive
4. Cannot be Reserved Word.

Next comes sentences, or here we are specifically talking about how do we code instruction in python. For simpler understanding let’s start off with arithmetic expressions.

                Assignment Statement: x=2

                Arithmetic assignment: x=x+2

                Output Statement: print(x)

So, what all did we come across in the previous three instructions, operators, constants, variables and function.

Numeric Expressions that are used in python are mentioned below, //pic of operator operation table

When we have so many operators for numeric expressions to perform simple calculation, there must be a way python must know which of them to do first, so to address this situation we will have to learn about the concept of operator precedence, i.e. which operator takes precedence over the others.

Highest precedence rule to lowest precedence rule:

1. Parentheses are always respected
2. Exponentiation (raise to a power)
3. Multiplication, Division, and Remainder
4. Addition and Subtraction
5. Left to right

Note: Remember in python3 when you perform integer division it produces a floating-point result.

Now lastly let’s see how to write paragraphs, Interactive python is good for experimenting programs of 3 to 4 lines, but most programs are much longer than that, so we type our python scripts in a file using an editor and then we tell python to run those commands that we have coded in the file. As a convention we add .py extension for python files.

Sequential flow of execution is followed by python interpreter unless it comes across some branching, looping or conditional statement. This means to say that when a program is running, that the flow of execution occurs from one step to the next. As programmers we set paths for the program to follow.

In python the variables are not declared by the programmer and the python interpreter resolves this during the interpretation time of the program and hence the language is dynamic. Python knows what type everything is, but some operators are prohibited as in you cannot add a numeric 1 to a string. We can ask python what type some named space is by using the built-in function, type().

There are certain scenario when the programmer would explicitly like to typecast a named space and to do so there are some built-in functions available to us, such as:

For python script to be interactive it must take input from the user and it does that by invoking a function, input() which takes a string argument and returns a string object containing the value entered by the user. The same operation is done by function raw_input() in python2.

Let’s say we want to read a number from the user then we must convert the string object to integer or float using the typecasting function which we have seen earlier.

Comments in python are prefixed by the ‘#’ symbol, when the interpreter comes across a line prefixed with ‘#’ then it doesn’t execute it or ignores it as comment. As a beginner in programming you might think why do we need to write comments in a program, the reasons are,

 -  Describe what is going to happen in a sequence of code

 -  Document who wrote the code or other ancillary information

 -  Turn off a line of code - perhaps temporarily

So now we have come to the end of introduction in python, and at this checkpoint we have pictured the edges of a big canvas about python and we will focus on the details of this canvas in the next post. Stay tuned for the next post on the topic of conditional statements and iterations, until then guys enjoy your time browsing through other posts in the blog!!