A Languages Table

Let’s look at a more realistic dictionary example. The following example creates a table that maps programming language names (the keys) to their creators (the values). You fetch creator names by indexing on language names:

>>> table = {'Python':  'Guido van Rossum',
...          'Perl':    'Larry Wall',
...          'Tcl':     'John Ousterhout' }
>>>
>>> language = 'Python'
>>> creator  = table[language]
>>> creator
'Guido van Rossum'

>>> for lang in table:                     # Same as: for lang in table.keys()
...     print(lang, '\t', table[lang])
...
Tcl     John Ousterhout
Python  Guido van Rossum
Perl    Larry Wall

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The last command uses a for loop, which we haven’t covered in detail yet. If you aren’t familiar with for loops, this command simply iterates through each key in the table and prints a tab-separated list of keys and their values. We’ll learn more about for loops in Chapter 13.

Dictionaries aren’t sequences like lists and strings, but if you need to step through the items in a dictionary, it’s easy—calling the dictionary keys method returns all stored keys, which you can iterate through with a for. If needed, you can index from key to value inside the for loop, as was done in this code.

In fact, Python also lets you step through a dictionary’s keys list without actually calling the keys method in most for loops. For any dictionary D, saying for key in D: works the same as saying the complete for key in D.keys():. This is really just another instance of the iterators mentioned earlier, which allow the in membership operator to work on dictionaries as well (more on iterators later in this book).