Python Identifiers:

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

Python does not allow punctuation characters such as @, $, and % within identifiers. Python is a case sensitive programming language. Thus India and india are two different identifiers in Python.

Here are following identifier naming convention for Python:

• Class names start with an uppercase letter and all other identifiers with a lowercase letter.

• Starting an identifier with a single leading underscore indicates by convention that the identifier is meant to be private.

• Starting an identifier with two leading underscores indicates a strongly private identifier.

• If the identifier also ends with two trailing underscores, the identifier is a language-defined special name.

Lines and Indentation:

One of the first caveats programmers encounter when learning Python is the fact that there are no braces to indicate blocks of code for class and function definitions or flow control. Blocks of code are denoted by line indentation, which is rigidly enforced.

The number of spaces in the indentation is variable, but all statements within the block must be indented the same amount. Both blocks in this example are fine:

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

However, the second block in this example will generate an error:

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

Multi-Line Statements:

Statements in Python typically end with a new line. Python does, however, allow the use of the line continuation character (\) to denote that the line should continue. For example:

total = item_one + \
        item_two + \
        item_three

Statements contained within the [], {}, or () brackets do not need to use the line continuation character. For example:

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

Quotation in Python:

Python accepts single ('), double (") and triple (''' or """) quotes to denote string literals, as long as the same type of quote starts and ends the string.

The triple quotes can be used to span the string across multiple lines. For example, all the following are legal:

word = 'word'
sentence = "This is a sentence."
paragraph = """This is a paragraph. It is
made up of multiple lines and sentences."""