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For example, one could define a dictionary having a string "toast" mapped to the integer 42 or vice versa. The keys in a dictionary must be of an immutable Python type, such as an integer or a string, because under the hood they are implemented via a hash function. This makes for much faster lookup times, but requires keys not change.
Python 2.7 and 3.x also support dict comprehensions (similar to list comprehensions), a compact syntax for generating a dictionary from any iterator: >>> square_dict = { i : i * i for i in range ( 5 )} >>> square_dict { 0 : 0 ,
For dictionaries with very few mappings, it may make sense to implement the dictionary using an association list, which is a linked list of mappings. With this implementation, the time to perform the basic dictionary operations is linear in the total number of mappings.
Python makes a distinction between lists and tuples. Lists are written as [1, 2, 3], are mutable, and cannot be used as the keys of dictionaries (dictionary keys must be immutable in Python). Tuples, written as (1, 2, 3), are immutable and thus can be used as keys of dictionaries, provided all of the tuple's elements are immutable.
Hashing is an example of a space-time tradeoff. If memory is infinite, the entire key can be used directly as an index to locate its value with a single memory access. On the other hand, if infinite time is available, values can be stored without regard for their keys, and a binary search or linear search can be used to retrieve the element.
Individual machine languages are specific to a family of processors; machine-language code for one family of processors cannot run directly on processors in another family unless the processors in question have additional hardware to support it (for example, DEC VAX processors included a PDP-11 compatibility mode).
Deutsches Rechtswörterbuch (Dictionary of Historical German Legal Terms) Lists of dictionaries cover general and specialized dictionaries, collections of words in one or more specific languages, and collections of terms in specialist fields. They are organized by language, specialty and other properties.
This is an index to notable programming languages, in current or historical use. Dialects of BASIC, esoteric programming languages, and markup languages are not included. A programming language does not need to be imperative or Turing-complete, but must be executable and so does not include markup languages such as HTML or XML, but does include domain-specific languages such as SQL and its ...