dict.md

Dictionary

Dictionaries are Python’s implementation of a data structure that is more generally known as an associative array. A dictionary consists of a collection of key-value pairs. Each key-value pair maps the key to its associated value.

Defining a dictionary

You can define a dictionary by enclosing a comma-separated list of key-value pairs in curly braces ({}). A colon (:) separates each key from its associated value.

For eg

d = { <key>: <value>, <key>: <value>, . . . <key>: <value> }

You can also construct a dictionary with the built-in dict() function. The argument to dict() should be a sequence of key-value pairs. A list of tuple works well for this: d = dict([ (<key>, <value>), (<key>, <value), . . . (<key>, <value>) ]) If the key values are simple strings, they can be specified as keyword arguments. d = dict( <key> = <value>, <key> = <value, . . . <key> = <value> )

Accessing Dictionary values

After defining a dictionary, we need to access the values assigned. Unlike list, we cannot access elements by their index numbers. So how to access them??

In dictionary, a value is retrieved by specifying its corresponding key in square bracket. ([])

For eg:

d[<key>]

Alternatively, we can also use d.get(<key>)

Updating an entry

To update an entry, just assign a new value to the existing key, i.e. d[<key>] = <new_value>

We can even create new entry in this fashion, i.e., d[<new_key>] = <new_value>

Deleting an entry

Use del statement, specifying the key to delete, i.e. del d[<key>]

Built-in Dictionary Method

As with strings and lists, there are several built-in methods that can be invoked on dictionaries. In fact, in some cases, the list and dictionary methods share the same name. (In the discussion on object-oriented programming, you will see that it is perfectly acceptable for different types to have methods with the same name.)

d.clear()

Clears a dictionary

d.get([, ])

Returns the value for a key if it exists in the dictionary

d.items()

Returns a list of key-value pairs in a dictionary

d.keys()

Returns a list of keys in a dictionary

d.values()

Returns a list of values in a dictionary

d.pop([, ])

Removes a key from a dictionary, if it is present, and returns its value

d.update()

Merges a dictionary with another dictionary or with an iterable of key-value pairs

Please refer /datatypes/examples/dict.py for more examples.

For more details and information, please external links and tutorials: Basics: http://www.tutorialspoint.com/python/python_dictionary.htm

Along with hands on tutorial: https://www.w3schools.com/python/python_dictionaries.asp