This document discusses Python data types like strings and lists. It explains that strings can be indexed and sliced, and are immutable. Lists can contain heterogeneous data types, are mutable, and also support indexing and slicing. Tuples are similar to lists but are immutable. Basic string and list operations like concatenation, multiplication, appending, and removing elements are demonstrated. The document also covers operator precedence and associativity in Python.

1. Programming in Python
Week-3 Content

2. Data types

3. Strings in Python
● Strings can be surrounded by single or double quotations.
● Can be multiline with 3 double/single quotation marks.
● Are stored in the memory as arrays
● Python doesn’t have character data type, the characters are
also internally stored as strings of length 1.
● You can access any characters of the string using indices.
● str_name[index] will give you the character at that index in
the string.
● str_name[start_index: end_index] will give substring
● Strings are immutable

5. Strings & Accessing characters

6. alpha = ‘c’ c
alpha
0
alpha = ‘coffee’ c
alpha
0
o f f e e
1 2 3 4 5
index
alpha[4]
e
4
f f e
2 3 4
alpha[2:5]

7. P Y T H O N
C L A S S E S
str1 =
str2 =
0 1 2 3 4 5
0 1 2 3 4 5 6
+
=
P Y T H O N
0 1 2 3 4 5
C L A S S E S
6 7 8 9 10 11 12
add =
N
5
str1[5]
S
9
add[9]

8. P Y T H O Nstr1 =
0 1 2 3 4 5
* 3
multiply =
P Y T H O N
0 1 2 3 4 5
Y T H O N
6 7 8 9 10 11
P Y T H O N
12 13 14 15 16 17
P

9. Now:
print(“Addition of %s and %s is %s”, %(str1, str2, add))
Initially:
print(“Addition of ” + str1 + “ and “ + str2 + “ is: “ + add )
Now: can be done for integers too
print(“Addition of %i and %i is %i”, %(num1, num2, add))

10. Python Lists
● Store multiple values in a single variable
● A single list may contain items of any data type
● len() can be used to get the length of the list
● append() can be used to add an element to an existing list
● remove() can be used to remove the first occurence of the
specified item in the list
● Each element of the list has a definite position - index starting from
0
● Lists are mutable

11. List Slicing
1 2 3 1 1 1
0 1 2 3 4 5
-6 -5 -4 -3 -2 -1
3 1 1 1
2 3 4 5
-4 -3 -2 -1
list[2:6]
3 1 1
2 3 4
-4 -3 -2
list[-4:-1]
3 1 1 1
2 3 4 5
-4 -3 -2 -1
list[2:]
1 2
0 1
-6 -5
list[:-4]

12. Tuples
● Identical to lists but created using ()
● Tuples are immutable
● Indexing and slicing works similar to strings and lists
● Use tuples instead of list when you don’t want data to be modified
● When the amount of data is too huge, tuples work faster than lists

13. Operator Precedence and Associativity in Python
● Combination of values, variables, operators and function calls makes a valid
expression.
● When there are more than 1 operators in an expression, rules of precedence
are used.
● If more than 1 operator is in the same group and hence has same precedence,
associativity is used to evaluate the expression.
● ** has right-to-left associativity, rest all operators have left-to-right associativity

18. Homework Questions