11.9: Glossary

mapping:

A relationship in which each element of one set corresponds to an element of another set.

dictionary:

A mapping from keys to their corresponding values.

key-value pair:

The representation of the mapping from a key to a value.

item:

In a dictionary, another name for a key-value pair.

key:

An object that appears in a dictionary as the first part of a key-value pair.

value:

An object that appears in a dictionary as the second part of a key-value pair. This is more specific than our previous use of the word “value”.

implementation:

A way of performing a computation.

hashtable:

The algorithm used to implement Python dictionaries.

hash function:

A function used by a hashtable to compute the location for a key.

hashable:

A type that has a hash function. Immutable types like integers, floats and strings are hashable; mutable types like lists and dictionaries are not.

lookup:

A dictionary operation that takes a key and finds the corresponding value.

reverse lookup:

A dictionary operation that takes a value and finds one or more keys that map to it.

raise statement:

A statement that (deliberately) raises an exception.

singleton:

A list (or other sequence) with a single element.

call graph:

A diagram that shows every frame created during the execution of a program, with an arrow from each caller to each callee.

memo:

A computed value stored to avoid unnecessary future computation.

global variable:

A variable defined outside a function. Global variables can be accessed from any function.

global statement:

A statement that declares a variable name global.

flag:

A boolean variable used to indicate whether a condition is true.

declaration:

A statement like global that tells the interpreter something about a variable.