![]() O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers. Get Python in a Nutshell, 2nd Edition now with the O’Reilly learning platform. In Python 2.4, the update method can also accept an iterable of key/value pairs as an alternative argument instead of a mapping, and can accept keyword arguments instead of or in addition to its only positional argument the semantics are the same as for passing such arguments when calling the built-in dict type, as covered in Dictionaries. Similarly, the pop method returns the same result as get, but if k is a key in D, pop also has the side effect of removing D (when x is not specified, and k is not a key in D, get returns None, but pop raises an exception). The setdefault method returns the same result as get, but if k is not a key in D, setdefault also has the side effect of binding D to the value x. The memory savings make the idiom usable for a loop on a huge dictionary, when what you want is to “consume” the dictionary in the course of the loop. Both items and popitem return dictionary items as key/value pairs, but using popitem consumes less memory, as it does not rely on a separate list of items. The popitem method can be used for destructive iteration on a dictionary. Iterating directly on a dictionary D is exactly like iterating on D. Iterating on the lists returned by items, keys, or values carries no such constraint. Each key is associated with a single value. An iterator consumes less memory than a list, but you must never modify the set of keys in a dictionary (i.e., you must never add nor remove keys) while iterating on any of that dictionary’s iterators. A dictionary contains a collection of indices and values (indices are also called keys). The iteritems, iterkeys, and itervalues methods return iterators equivalent to these lists (iterators are discussed in Iterators). If you call more than one of these methods without any intervening change to the dictionary, however, the order of the results is the same for all. The items, keys, and values methods return their resulting lists in arbitrary order. Python dictionaries are a powerful and versatile tool for data engineering, providing fast lookups, flexible data storage, easy iteration, and memory efficiency. Removes and returns an arbitrary item (key/value pair) Removes and returns D if k is a key in D otherwise, returns x (or raises an exception if x is not given) Returns D if k is a key in D otherwise, sets D equal to x and returns x Removes all items from D, leaving D emptyįor each k in D1, sets D equal to D1 ![]() Returns D if k is a key in D otherwise, returns x (or None, if x is not given) Returns an iterator on all items (key/value pairs) in D In a list, the index positions have to be integers in a dictionary, the indices can be. Returns a new list with all items (key/value pairs) in D A dictionary is like a list, but more general. Returns True if k is a key in D otherwise, returns False, just like k in D ![]() Returns a shallow copy of the dictionary (a copy whose items are the same objects as D’s, not copies thereof) Basically, Python dictionaries are an unordered collection of data values. ![]()
0 Comments
Leave a Reply. |