working-with-data.md

Working with Data

Data Types

There are a number of data types in Python that represent types of information that a variable can store. Here are a few examples:

Integers:

• a data type in Python that stores an integer such as: -5, 0, 6, 143, -1745

• Assignment Statement - Example: age = 43

Floats:

• a data type in Python that stores a decimal value such as: 3.14, -2.71828

• Assignment Statement - Example: price = 4.99

Strings:

Strings are sequences of letters and numbers, or in other words, chunks of text. They are surrounded by two quotes. The part inside the quotes "" is a string literal, meaning that it should be literally copied and not interpreted as a command.

• a data type in Python that stores text

• each character is stored using an index value

• Assignment Statement - Example: lastName = "Guse"

• Find the length of String (# of characters including spaces) using the len() function: Example: len(lastName) has a value of 4

>>> lastName = "Guse"
>>> print lastName
Guse
>>> print lastName[0]
G
>>> print lastName[3]
e
>>> print len(lastName)
4

Booleans:

The values True and False are called Boolean values. They often result as the value of a conditional expression, even if you don't explicitly see them. See them in action by looking at the following examples in the interactive python shell

>>> print 5 < 10
False
>>> x = 15
>>> print x == 15
True
>>> print 5 < 10
False
>>> x = 15
>>> print x == 15
True

They can be used in conditional statements such as if/elif/else.

paid = True
if paid:
    print "Thank you for paying your bill."
else:
    print "Please pay what you owe."

Tuples

A tuple can store strings, integers, and other data types. Here is an example:

>>> myPoint = (3,4)
>>> print myPoint[0]
3
>>> print myPoint[1]
4
>>> myPoint = (3,4)
>>> print myPoint[0]
3

Variables

Variables have a type determined by their assignment statement. For example, in the code

score = 4

the variable **score **is an integer, because it has been assigned an integer value. In this code,

mark = 87.4

the variable **mark **is a float. Sometimes it is not so obvious. In the following calculation,

total = score * 2 + 5

the variable **total **is an integer because only integer values have been used in the calculation. However, in this code,

average = (5 + 6 + 4) / 3

the variable **average **is a float because of the division operator_ (division always produces a float)_, even though all values in the calculation are integers. Whereas, in the code

hundreds = 563 // 100

the variable **hundreds **is an integer because // is the integer division operator. If you are not sure about the type of a variable you can use the type() function. For example,

>> type(average)
<class 'float'>
>> type(mark)
<class 'int'>

Style and Variable Naming Rules

You cannot use any variable name in Python. Here are the rules that must be followed.

The Rules

• Variables names must **start **with a **letter **or an underscore, such as: _password, my_password
• The **remainder **of your variable name may consist of letters, **numbers **and underscores. password1, n00b. ...
• Names are case sensitive. my_password, MY_PASSWORD, and My_Password are each a different variable.

Style

• Your variable names should describe what the variable represents, so a, b, x, and **y **are not very good names. Better names would be score, average, name, etc.
• If you wish to use a combination of names, there are two styles that are common (since you cannot use spaces in your variable name). The underscore character can be used: final_score, or you can use capitalization: finalScore.