Comparison of programming languages (associative array): Difference between revisions

Revision as of 05:29, 22 January 2016

Revision as of 05:39, 22 January 2016

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To access an entry in Python simply use the array indexing operator. For example, the
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>>> <code>phonebook['Sally Smart']</code> would return <code>
'555-9999'</code>.

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An example loop [[iterator#Python|iterating]] through all the keys of the dictionary:

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>>> for key in phonebook:

... print key, phonebook[key]

Sally Smart 555-9999

J. Random Hacker 553-1337

John Doe 555-1212

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Iterating through (key, value) tuples:

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>>> for key, value in phonebook.itemsiteritems():

... print key, value

Sally Smart 555-9999

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J. Random Hacker 553-1337

John Doe 555-1212

Dictionaries can also be constructed with the <code>dict</code> builtin, which is most commonly found inside list comprehensions and generator expressions, and it takes a key-value list:

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dict((key, value) for key, value in phonebook.items() if 'J' in key)

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Dictionary keys can be individually deleted using the del statement. The corresponding value can be returned before the key-value pair are deleted using the pop method of dict types:

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>>> del phonebook['John Doe']

>>> val = phonebook.pop('Sally Smart')

assert>>> phonebook.keys() == ['J. Random Hacker'] # Only one key left

['J. Random Hacker']

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Python 2.7 and 3.0x also supports dictionary comprehensions, a compact syntax for generating a dictionary from any iterator:

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>>> square_dict={i:i*i for i in range(5)}

assert>>> square_dict ==
{0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

dict((>>> {key,: value) for key, value in phonebook.itemsiteritems() if 'J' in key)}

{'J. Random Hacker': '553-1337', 'John Doe': '555-1212'}

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