In the previous article, we have seen how to write a simple hello world program. Before going into more details lets first go through python identifiers, reserved keywords and other important basic syntax rules.

Python Identifiers

A Python identifier is a name used to identify a variable, function, class, module or other objects. An identifier starts with a letter [A-Z,a-z] or an underscore (_) followed by zero or more letters, digits [0-9] or underscores.

Identifier can not contain special characters such as @, $, and % and they are case sensitive.

Naming convention for python identifiers are as below:

• To declare a private identifier it should start with a single leading underscore.
• To declare a strongly private identifier it should start with two leading underscore. 
• Class names start with an uppercase letter. Others start with a lowercase letter.
• If the identifier also ends with two trailing underscores, the identifier is a language-defined special name.

Reserved Words

Like in every language, python also have a list of reserved keywords. These reserved words cannot be used as constant or variable or any other identifier names. All the Python keywords contain lowercase letters only. Below is the list of python reserved keywords.

Lines and Indentation

Unlike in other languages, in python blocks of code are denoted by line indentation. Python does not provides braces to indicate blocks of code. The number of spaces in the indentation is variable, but all statements within the block must be indented the same amount.

Thus, in Python all the continuous lines indented with the same number of spaces would form a block as shown in below example.

if True:
   print "True"
else:
   print "False"

Multi-Line Statements

Statements in Python typically end with a new line. In order to have multiline statement in Python one has to use the line continuation character (\) to denote that the line should continue as shown in example.

total = item_one + \
        item_two + \
        item_three

Statements contained within the [], {}, or () brackets do not need to use the line continuation character as shown in below.

days = ['Monday', 'Tuesday', 'Wednesday',
        'Thursday', 'Friday']

Quotation in Python

To denote a string literals python allows use of single ('), double (") and triple (''' or """ ) quotes, as long as the same type of quote starts and ends the string.

word = 'word with single quote to denote string’

sentence = "This is a sentence with double quote to denote string"

paragraph = """This is a paragraph. It is
made up of multiple lines and sentences with triple quote to denote string"""

Multiple Statements on a Single Line

The semicolon ( ; ) allows multiple statements on the single line given that neither statement starts a new code block. Here is a sample snip using the semicolon −

import sys; x = 'foo'; sys.stdout.write(x + '\n')

Multiple Statement Groups as Suites

A single code block having multiple statements are called suites in Python. Compound or complex statements, such as if, while, def, and class require a header line and a suite.

Header lines begin the statement (with the keyword) and terminate with a colon ( : ) and are followed by one or more lines which make up the suite. For example −

if expression : 
   suite1
elif expression : 
   suite 2
else : 
   suite3

Comments in Python

A hash sign (#) that is not inside a string literal begins a comment. All characters after the # and up to the end of the physical line are part of the comment and the Python interpreter ignores them.

#!/usr/bin/python
# First comment
print "Hello, World!” # second comment

Using Blank Lines

Python totally ignores blank lines(A line containing only whitespace, possibly with a comment).

Waiting for the User

The following line of the program displays the prompt, the statement saying “Press the enter key to exit”, and waits for the user to take action.

#!/usr/bin/python
raw_input("Press the enter key to proceed.”)

That’s it for now :). We will explore more of it as we learn more in next articles.