Data Type - 'dict' for Dictionary Table

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∟Data Type - 'dict' for Dictionary Table

This section describes the 'dict' data type, which stores a collection of key-value pairs. 'list' data objects are mutable.

What Is the "dict" Data Type? "dict" is the mutable dictionary data type in Python. Each element in a "dict" object is a key-value pair, where the key refers to a hashable object, and the value refers an arbitrary object.

"dict" data type is also called hash table or associated array in other programming languages.

"dict" data type has the following main Features.

1. "dict" data objects can be created in several ways:

Using key-value pairs within braces like {'foo': 100, 'bar': 200}.
Using the cast function, dict(object), like dict(foo=100, bar=200).

2. "dict" data type provides an array-style expression to access the element of a given key.

>>> x = {'foo': 100, 'bar': 200}
>>> type(x)
<class 'dict'>

>>> e = x['foo']
>>> e
100
>>> type(e)
<class 'int'>

3. "dict" data type is a mutable data type. Once a "dict" data object is created to store key-value pairs, Its content can be changed: key-value pairs can be added, removed and/or updated.

>>> x = {'foo': 100, 'bar': 200}
>>> id(x)
4457650624

>>> x['new'] = 300
>>> x
{'foo': 100, 'bar': 200, 'new': 300}

>>> del x['bar']
>>> x
{'foo': 100, 'new': 300}

>>> x['foo'] = 101
>>> x
{'foo': 101, 'new': 300}

>>> id(x)
4457650624

4. "dict" objects support the following operations:

    Syntax   Operation       Note
----------   -------------   -----------------------
     x | y   Merge           Creates a new "dict"
    x |= y   Merge           Updates x
    k in x   Look up         k is an object
k not in x   Look up         Same as !(k in x)
  x[k] = o   Update          Update pair
  del x[k]   Delete          Delete pair

5. Some built-in functions are provided for "dict" objects.

iter(x) - Returns an iterator object over the keys of this "dict" object.
len(x) - Returns the number of elements in this "dict" object.
list(x) - Returns a "list" object of of all the keys in this "dict" object.
reversed(x) - Returns an iterator over the keys in reversed order of this "dict" object.

6. Some instance/class methods are provided for "dict" objects.

dict.clear() - Instance method removes all elements from this dictionary.
dict.copy() - Instance method returns a new "dict" object with same elements as in this dictionary.
dict.fromkeys(iterable, value) - Class method returns a new "dict" object with keys extracted from the given iterable object. Every key will be assigned to the same given value.
dict.get(key) - Instance method returns the value associated with the given key in this dictionary.
dict.items() - Instance method returns an iterable object holding all items as tuples in this dictionary.
dict.keys() - Instance method returns an iterable object holding all keys in this dictionary.
dict.pop(key) - Instance method pops out the value of the given key from this dictionary.
dict.popitem() - Instance method pops out last item as a tuple from this dictionary.
dict.setdefault(key, default) - Instance method return value of the given key, if it exists in the Otherwise, add the given key with the default value.
dict.update(other) - Instance method updates this dictionary by merging items from the given other dictionary.
dict.values() - Instance method returns an iterable object holding all values in this dictionary.