Types in Python

In Python, every piece of data we deal with has a type.

Some of the most basic types are:

• int for integers (e.g. -42, 0, 3, 4567)
• float for numbers that have decimal points, (e.g. 3.14159, 0.5, -67.0,1.0, 6.0221409e+23)
• bool for the special values True and False

Some commonly used types that involve collections of things are:

• str for sequence of characters (e.g. 'Chris', 'UCSD', 'Computer Science & Engineering', '6th College')
• list for lists of items, where the items can be of any type, or a mix of types. Examples:
  • [6, 10, 4, 17]
  • ['Revelle', 'Muir', 'Marshall', 'Warren', 'Roosevelt', 'Sixth']
  • ['Chris','Diaz',9876544,True]
• dict for dictionarires of items, which are associations of keys and values. Examples:
  • { 'one' : 'uno', 'two' : 'dos', 'three' : 'tres' }
  • { 'fname' : 'Phill', 'lname' : 'Conrad', 'pid' : 1234567, 'gpa': 3.77, 'isHappy' : True }

There are additional types that are less commonly discussed in “introductory programming”, but that may end up being useful.

Here are a few of them:

• NoneType is a special type used for the the value that gets returned from a function that, literally, doesn’t return anything at all. For example:

    def returnsNothing(x):
        x = x + 1
  

    >>> returnsNothing(3)
    >>> type(returnsNothing(3))
    <type 'NoneType'>
    >>>
  

• Unicode for sequences of a larger set of characters (e.g. u'四', u'piñata').
  • A python file that contains these characters may need to have a special comment at the top to avoid errors when compiling.
  • Example special comment for unicode: # -*- coding: utf-8 -*-
• tuple is similar to list, but the object created is immutable, meaning it cannot be changed after it is initially created.