Python- Review- Lesson no-2

Good Morning Dear Students



The correct responses  of the worksheet shared yesterday are as follows (in Maroon color):

1. Python is A high level language.
2.Python uses an interpreter.
3. Following are true for Python

• Is simple
• Platform independent and portable
• Has a huge Library

4. Following are terms related to Python

• Keywords
• operators
• punctuators

5. Keywords are

• are special words which are reserved by Python .
• are not allowed to be used as variables in Python.
• are case-sensitive.

I hope you have a better understanding of the basic concepts of Python now.
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By the end of this session, you will be able to

• Define the term "Identifiers"
• Identify the rules to define identifiers
• Define identifiers as per the need of the program.
• Identify VALID and INVALID identifiers

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Today our focus will be the concept of identifiers.
(Please take down the following concepts in your registers):

As you know that identifiers are 

• very important in programming. 
•  the building blocks of a program.
•  So we need to create them wisely.

 RULES to follow while defining identifiers 

1.   

      1.  Identifiers can be a combination of letters in lowercase (a to z) or uppercase (A to Z) or digits (0 to 9) or an underscore _ Names like myClass, var_1 and print_this_to_screen, all are valid example.

1     2.  An identifier cannot start with a digit. eg. 1variable is invalid, but variable1 is perfectly fine.

2     3.    Keywords cannot be used as identifiers. eg. print cannot be used as an identifier. 

3    4.    We cannot use special symbols like !, @, #, $, % etc. in our identifier. The only symbol allowed is the underscore i.e. "_" eg. var_1

4     5.  An identifier can be of any length.

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Things to Remember

1. Python is a case-sensitive language. This means, Variable and variable are not the same. Always name identifiers that make sense.

2. While, c = 10 is valid. Writing count = 10 would make more sense and it would be easier to figure out what it does even when you look at your code after a long gap.

3. Multiple words can be separated using an underscore, this_is_a_long_variable.

The following are some VALID identifiers:

MyFile

MYFILE

 CHK

 Z2t0Z29

DATE9_7_77

 _DS

 FILE13

HJI3_JK

The following are some INVALID identifiers( along with the reason):

DATA-REC-  contains special character – (hyphen) (other than A-Z,a-z,_(underscore))

 29CLCT- starting with a digit

 break - reserved word

 My.file – contains special character dot (.)

EXERCISE

Q1. Find whether the following Python identifiers are valid or not. Give reasons, if not valid:
   1.      happy_10
2.      For
3.      for
4.      10find
5.      Count
6.      Count 1
7.      cout@1
8.      1count
9.      Count_1
10.  if
11.  if#
12.  while
13.  while 2
14.  while_2
15.  while.nd
16.  while2

Please do the above exercise in your notebook. We will discuss the answers tomorrow.