Integer Data can be decimal, octal or hexadecimal. Octal integer use O (both upper and lower case) to denote octal digits and hexadecimal integer use OX (both upper and lower case) and L (only upper case) to denote long integer.

(i) An identifier must start with an alphabet (A..Z or a..z) or underscore (_)..
(ii) Identifiers may contain digits (0 .. 9).
(iii) Python identifiers are case sensitive i.e. uppercase and lowercase letters are distinct. (iv) Identifiers must not be a python keyword.
(v) Python does not allow punctuation character such as %,$, @ etc., within identifiers.

(i) In Python, comments begin with hash symbol (#). The lines that begins with # are considered as comments and ignored by the Python interpreter.
(ii) Comments may be single line or no multilines. The multiline comments should be enclosed within a set of # as given below.
# It is Single line Comment
# It is multiline comment
which contains more than one line #

x = int(input ("Enter Number 1")
y = int(input("Enter Number 2")
print ("The sum of", x, " and ", y, "is", x+y)

(i) In Python, programs can be written in two ways namely Interactive mode and Script mode.
(ii) The Interactive mode allows us to write codes in Python command prompt >>> whereas in script mode programs can be written and stored as separate file with the extension.
(iii) py and executed. Script mode is used to create and edit python source file.