Lecture 1: Introduction to Programming

Agenda for the Class:

Python in-built datatypes
Basic mathematical operators and Precedence order
Python Interpreter vs Python for Scripting

Firstly we'll focus on the datatypes.

Numeric
Strings
Lists

General format for Assigning a variable a value: Variable_name = Variable_Value

We Do not mention datatype while assigning a variable a value in Python. (i.e. Dynamically Typed)
= is used to assign a variable a value. ( L Value and R value)
A variable name must follow certain naming conventions. Example: '23', 'len' can be variable names.
There is no such thing as "variable declaration" or "variable initialization" in Python. It's only variable assignment

Numeric data



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a=1
b=3.14
# Assigning value 1 to variable a and 3.14 to variable b

Mathematical Operations on Variables:

Add ('+')
Multiple ('*')
Subtract ('-')
Divide ('/')
Modulo ('%')
Exponentiation (**)

Order of Precedence

Exponent > (Multiple, Divide, Modulo) > (Add, Subtract)



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a = 20
b = 10
c = 15
d = 5
e = 0



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e = (a + b) * c / d       #( 30 * 15 ) / 5
print ("Value of (a + b) * c / d is ",  e)



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e = ((a + b) * c) / d     # (30 * 15 ) / 5
print ("Value of ((a + b) * c) / d is ",  e)



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e = (a + b) * (c / d);    # (30) * (15/5)
print ("Value of (a + b) * (c / d) is ",  e)



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e = a + (b * c) / d;      #  20 + (150/5)
print ("Value of a + (b * c) / d is ",  e)

In case you are using Python 2 and want floating point division (e.g: 4/3 --> 1.33333333333 and not 4/3 --> 1) :

 For Python shell type in : from __future__ import print_function, division
 For a ".py" file : Use that import statement in the beginning of your Python file.

Strings

Immutable datatype
String enclosed within " String" or 'String'



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course_name = "Introduction to Programming"
question = "Having a good time ? ;)"
print(course_name)
print(question)

Operations on Strings

Since strings are immutable, we can't change the value stored in a string
We can concatenate ('join') multiple strings.
Slice/substring operations



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string_1 = "Hello World!"
n = len(string_1)  # "len" gives us the number of characters in the string
print(string_1 + " has", n , "characters")

Indexing : Every charcater of the string can be accessed by it's position in the string.
Indexing starts from zero.
Syntax string_name[index_number]

Example:



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print(string_1[0])
print(string_1[1])



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print(string_1[-2])

Negative Indexing: string[-1] gives us the last character string[-2] gives us the second last character and so on...

Slicing operations

Syntax:

string_name[start_index,end_index]



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print(string_1[0:2])
print(string_1[5 : len(string_1)])



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print(string_1[0:4]+string_1[4:len(string_1)])

Lists

Initializing syntax: \n list_name = [value_1,value_2,...,value_n]
Behaviour Similar to strings
Mutable
Can contain multiple data types.



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primes = [2,3,5,8,11]
print(primes)
print(primes[0])
print(len(primes))



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classroom = ['L','T', 1]
print(classroom)
print((classroom[2]+ 4))

What to do next?

1.Play around in the python interpreter to explore various functionalities
2.Understand the rules to name variables.



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