Topics covered: Strings Lists Tuples Operator precedence and Associativity

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