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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.
An attacker could supply the program with the string "session.update(authenticated=True)" as data, which would update the session dictionary to set an authenticated key to be True. To remedy this, all data which will be used with eval must be escaped, or it must be run without access to potentially harmful functions.
Strings are represented in C literal style: "This is a plist string\n"; simpler, unquoted strings are allowed as long as they consist of alphanumericals and one of _$+/:.-. Binary data are represented as: < [hexadecimal codes in ASCII] >. Spaces and comments between paired hex-codes are ignored. Arrays are represented as: ( "1", "2", "3 ...
The procedure begins by examining the key; null denotes the arrival of a terminal node or end of a string key. If the node is terminal it has no children, it is removed from the trie (line 14). However, an end of string key without the node being terminal indicates that the key does not exist, thus the procedure does not modify the trie.
A list containing the string "bencode" and the integer -20 is encoded as l7:bencodei-20ee. Dictionaries are encoded as d<pairs>e. Begins with d and ends with e. Contains key-value pairs. Keys are byte strings and must appear in lexicographical order. Each key is immediately followed by its value, which can be any bencoded type. Examples:
In PHP and R, all arrays can be associative, except that the keys are limited to integers and strings. In JavaScript (see also JSON), all objects behave as associative arrays with string-valued keys, while the Map and WeakMap types take arbitrary objects as keys. In Lua, they are used as the primitive building block for all data structures.
Given two strings a and b on an alphabet Σ (e.g. the set of ASCII characters, the set of bytes [0..255], etc.), the edit distance d(a, b) is the minimum-weight series of edit operations that transforms a into b. One of the simplest sets of edit operations is that defined by Levenshtein in 1966: [2] Insertion of a single symbol.
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.