Python Programming

lists). Try typing into the shell stuff['hello'] and stuff['chat'] and stuff['goodbye']: >>> stuff['hello'] 'Hello there, how are you?' >>> stuff['chat'] 'How is the weather?' >>> stuff['goodbye'] 'It was nice talking to you!' >>>

Ge t t i n g t h e Si ze o f Di c t i o n ar i e s w i t h len() You see, instead of putting an integer index in between the square brackets, you put a key string index. This will evaluate to the value for that key. You can get the size (that is, how many key-value pairs in the dictionary) with the len() function. Try typing len(stuff) into the shell: >>> len(stuff) 3 >>>

The list version of this dictionary would have only the values, and look something like this: listStuff = ['Hello there, how are you?', 'How is the weather? ', 'It was nice talking to you!']

The list doesn't have any keys, like 'hello' and 'chat' and 'goodbye' in the dictionary. We have to use integer indexes 0 , 1, and 2.

T h e D i f fe r en c e B e t w e e n Di c t i o n ar i e s a n d L i s t s Dictionaries are different from lists because they are u n o r d e r e d . The first item in a list named listStuff would be listStuff[0] . But there is no "first" item in a dictionary, because dictionaries do not have any sort of order. Try typing this into the shell: >>> favorites1 = {'fruit':'apples', 'animal':'cats', 'number':42} >>> favorites2 = {'animal':'cats', 'number':42, 'fruit':'apples'} >>> favorites1 == favorites2 True >>>

As you can see, the expression favorites1 == favorites2 evaluates to True because dictionaries are unordered, and they are considered to be the same if they have the same key-value pairs in them. Lists are ordered, so a list with the same values in them but in a different order are not the same. Try typing this into the shell: >>> listFavs1 = ['apples', 'cats', 42] >>> listFavs2 = ['cats', 42, 'apples'] >>> listFavs1 == listFavs2 False 105