Module 2.3 Data Types

Strings

A sequence of characters that can be stored in a variable

String Literal

String value specified in the source code of the program

E.g. “class”, “python”, “this is a string!”

input()

gives the user a prompt and then reads in a string from the user

len()

s a built-in function that can be used to find the length of a string (and any other sequence type)

String Concatenation

A program can add new characters to the end of a string

Container

A construct used to group related values together and contains references to other objects instead of data

List

A container created by surrounding a sequence of variables or literals within brackets []

Element

an item in a list

Index

contained elements in a list are ordered by position within the list, starting with 0
are mutable — can be changed

Sequence-type Functions

Tuples

An immutable container, which means the elements within can’t be changed

Sequence type structure that supports sequence functions such as len(), indexing, etc.

Is created using parenthesis

useful to ensure values are not changed when specified

Set

an unordered collection of unique elements

set()

accepts a sequence-type iterable object (list, tuple, string, etc.)

Set literal

written using { } with elements separated by commas

e.g. integers_set = {1, 2, 3, 4, 5}

Mutable Sets (add/remove elements)

Set Operations

Dictionary

Python container used to describe associative relationships

Associates keys with values

Key

Term that can be located in a dictionary

Must be unique

Value

describes some data associated with a key and can be duplicated

Key-value pairs

keys need to be immutable types such as numbers, strings, or tuples, while a value can be any type

Dictionary Example

favorite_basketball_playes = {‘Lebron James’: 6, ‘Stephen Curry’: 30}

Keys: ‘Lebron James’ and ‘Stephen Curry’

Values: 6 and 30

Type Conversions

conversion of one type to another, such as an int to a float

Implicit Conversion

a type conversion automatically made by the interpreter, usually between numeric types

The result of an arithmetic operation like + or * will be a float only if either operand of the operation is a float

Conversion Functions

Binary Number

Each memory location is composed of bits (0s and 1s), a processor stores a number using base 2

Decimal Number

Numbers represented in base 10, where each digit must be 0-9 and each digit’s place is weighed by increasing powers of 10

format()

A function that allows the programmer to create a string with placeholders that are replaced by values or variable values at execution

Replacement field

A placeholder surrounded by curly braces

String Formatting Example

Values inside the format() parentheses are inserted into the replacement fields in the string

Formatting Strings

Which of the following are NOT data type names in Python?

Math ; String ; while ; double ; char ; if

Which of the following are data type names in Python?

float ; int ; str ; bool

Match the literal value to its python data type.

1, 1.0, False, “integer”

1 - int

1.0 - float

False - bool

“integer” - str

Match the literal value to its python data type.

123, 22.5, True, “round”

123 - int

22.5 - float

True - bool

“round” - str

Which of the following would be the best data type for a variable to store a friend's name?

str

A chef would like to record the number of guests that visit his restaurant in a day. Which data type would best represents this quantity?

int

Consider the following sequence of instructions:

a = 2 + 2
b = a * 2
a = b - 2
x = a * b

x

What will the variable x evaluate to on the last line?

48

What will the variable x evaluate to on the last line?

x = 1
y = 8
x = y + 1
y = x - 1
x = x + 1
y = y - 1
x = x - y
 
x

3

What will the variable x evaluate to on the last line?

x = 15
y = 3
x = x + 1
y = y - 1
x = x + y
 
x

18

What will the variable x evaluate to on the last line?

a = 16
x = a + 16
a = 8
 
x

32

Which of the following would be the best data type for a variable to store an alpha-numeric serial number?

str

A physician would like to record the heights of his patients in meters. Which data type would best represents this quantity?

float

Consider the following sequence of instructions:

a = 2 + 3
b = a - 5
a = a + 2
x = a * b

x

What will the variable x evaluate to on the last line?

0

What will the variable x evaluate to on the last line?

x = 8
y = 11
x = x + 1
y = y - 1
x = x + y
 
x

19

What will the variable x evaluate to on the last line?

x = 4
y = 6
x = y + 1
y = x - 1
x = x + 1
y = y - 1
x = x - y
 
x

3