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Some object-oriented languages such as C#, C++ (later versions), Delphi (later versions), Go, Java (later versions), Lua, Perl, Python, Ruby provide an intrinsic way of iterating through the elements of a collection without an explicit iterator. An iterator object may exist, but is not represented in the source code.
Python sets are very much like mathematical sets, and support operations like set intersection and union. Python also features a frozenset class for immutable sets, see Collection types. Dictionaries (class dict) are mutable mappings tying keys and corresponding values. Python has special syntax to create dictionaries ({key: value})
Python's tuple assignment, fully available in its foreach loop, also makes it trivial to iterate on (key, value) pairs in dictionaries: for key , value in some_dict . items (): # Direct iteration on a dict iterates on its keys # Do stuff
The basic definition of a dictionary does not mandate an order. To guarantee a fixed order of enumeration, ordered versions of the associative array are often used. There are two senses of an ordered dictionary: The order of enumeration is always deterministic for a given set of keys by sorting.
Iterating over a container is done using this form of loop: for e in c while w do # loop body od; The in c clause specifies the container, which may be a list, set, sum, product, unevaluated function, array, or object implementing an iterator. A for-loop may be terminated by od, end, or end do.
In mathematics, iteration may refer to the process of iterating a function, i.e. applying a function repeatedly, using the output from one iteration as the input to the next. Iteration of apparently simple functions can produce complex behaviors and difficult problems – for examples, see the Collatz conjecture and juggler sequences .
Recursion is sometimes referred to in management science as the process of iterating through levels of abstraction in large business entities. [20] A common example is the recursive nature of management hierarchies , ranging from line management to senior management via middle management .
One common cause, for example, is that a programmer intends to iterate over sequence of nodes in a data structure such as a linked list or tree, executing the loop code once for each node. Improperly formed links can create a reference loop in the data structure, where one node links to another that occurs earlier in the sequence.