Dict

The pre-defined functions (methods) allow manipulation, querying, and management of dictionary objects. Below is a detailed explanation of each method, including the nine listed in the announcement and the two additional standard methods (setdefault() and fromkeys()).

1. fromkeys()

Creates a new dictionary with the specified keys, all assigned the same value (default is None).

Syntax: new_dict = dict.fromkeys(keys, value=None)

Key Notes:

• The static method is called on the dict class, not an instance.
• Useful for initializing dictionaries with default values.

2. get(key[, default]):

Returns the value for the specified key. If the key does not exist, it returns None or a specified default value.

Syntax: value = dictobj.get(key, default=None).

Key Notes:

• Safer than direct key access (d[key]) as it avoids KeyError.
• Commonly used for accessing values with fallback options.

3. keys():

Returns a view object of the dictionary’s keys.

Syntax: keys = dictobj.keys()

Key Notes:

• The view object is dynamic, reflecting changes to the dictionary.
• Useful for iterating over keys.

4. values():

Returns a view object of the dictionary’s values.

Syntax: values = dictobj.values().

Key Notes:

• Like keys(), the view object is dynamic.
• Useful for accessing all values without keys.

5. items():

Returns a view object of the dictionary’s key-value pairs as tuples.

Syntax: items = dictobj.items().

Key Notes:

• Useful for iterating over both keys and values simultaneously.
• The view object is dynamic, reflecting dictionary changes.

6. update([other]):

Updates the dictionary with key-value pairs from another dictionary or iterable, overwriting existing keys.

Syntax: dictobj.update(other).

Key Notes:

• Modifies the dictionary in place.
• Can accept another dictionary or an iterable of key-value pairs (e.g., list of tuples).

7. setdefault(key[, default]):

Returns the value for the specified key. If the key does not exist, it inserts the key with the default value (or None) and returns it.

Syntax: value = dictobj.setdefault(key, default=None)

Key Notes:

• Combines get() and key insertion in one operation.
• Useful for initializing missing keys (e.g., in counting scenarios).

8. clear():

Removes all key-value pairs from the dictionary, leaving it empty.

Syntax: dictobj.clear().

Key Notes:

• Modifies the dictionary in place (same memory address).
• The dictionary becomes {} but retains its identity.

9. copy():

Creates a shallow copy of the dictionary, allowing modifications to the copy without affecting the original.

Syntax: dictobj2 = dictobj1.copy().

Key Notes:

• Returns a new dictionary with a different memory address.
• Shallow copy means nested objects (e.g., lists as values) are not deeply copied.

10. pop(key):

Removes and returns the value associated with the specified key. Raises KeyError if the key does not exist.

Syntax: value = dictobj.pop(key).

Key Notes:

• Modifies the dictionary by removing the specified key-value pair.
• Useful for extracting and deleting a specific entry.

11. popitem():

Removes and returns the last inserted key-value pair as a tuple. Raises KeyError if the dictionary is empty.

Syntax: key_value = dictobj.popitem().

Key Notes:

• Since Python 3.7+, dictionaries maintain insertion order, so popitem() removes the last added pair.
• Useful for stack-like operations.

12. del:

The del statement is a Python keyword used to remove objects or specific components of objects, such as dictionary key-value pairs, list elements, or entire variables. In the context of dictionaries, del is commonly used to delete a specific key-value pair or the entire dictionary.

• Removes the key-value pair associated with key.

• Raises KeyError if key does not exist.

• Removes the dictionary object entirely, making it inaccessible.

• Subsequent access raises NameError.