Cmput174 dic onaries 15 keys and values getkey returns

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Unformatted text preview: pairs to a Dic$onary • To add a new value, assign it to a new key • Dic-onaries do not need to use append() or insert() like lists do. CMPUT174  ­ ­ Dic-onaries 13 Upda$ng a Value in a Dic$onary • To update a value, re ­assign it • You can change the value associated with a key by re ­ assigning • For example: my_dict = {“greeting”:”Hello”}
 print(my_dict[“greeting”]) # outputs Hello
 my_dict[“greeting”] = “Hi”
 print(my_dict[“greeting”]) # outputs Hi" CMPUT174  ­ ­ Dic-onaries 14 Keys and values • A run-me error occurs if you try to access a dic-onary with a key which is not in it: • The get(key) method handles this error nicely: default parameter! CMPUT174  ­ ­ Dic-onaries 15 Keys and values • get(key) returns the value OR a default parameter: • To get all keys or all values in a dic-onary: CMPUT174  ­ ­ Dic-onaries 16 Membership tests • Checking if a key is in the dic-onary • To check if a value is in the dic-onary, we need to get the list of values first: CMPUT174  ­ ­ Dic-onaries 17 Dele$ng Pairs from a Dic$onary • There are two ways of removing pairs from a dic-onary CMPUT174  ­ ­ Dic-onaries 18 Dele$ng Pairs from a Dic$onary • Using pop() on a list removes and returns the last element • Dic-onaries don’t have a “last” element, so popitem() removes and returns some key/value pair from a dic-onary • Using pop(key) on a dic-onary requires an argument which is the key to remove. If the key exists, it is removed and the value is returned. If it does not, an error occurs. • Using pop(key, default) on a dic-onary will return default if...
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This document was uploaded on 03/02/2014.

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