A dictionary in Python is a mutable, unordered collection of key-value pairs, where each key must be unique. Dictionaries are useful for storing and retrieving data efficiently based on a specific key. Here is the syntax and an example of using dictionaries in Python:
Syntax:
# Creating an empty dictionary
my_dict = {}
# Creating a dictionary with initial values
my_dict = {key1: value1, key2: value2, key3: value3}
# Accessing a value using a key
value = my_dict[key]
# Modifying a value
my_dict[key] = new_value
# Adding a new key-value pair
my_dict[new_key] = new_value
# Deleting a key-value pair
del my_dict[key]
# Checking if a key exists in the dictionary
if key in my_dict:
# Do something
# Getting the list of keys
keys = my_dict.keys()
# Getting the list of values
values = my_dict.values()
# Getting the list of key-value pairs as tuples
items = my_dict.items()
Example:
# Creating a dictionary with student information
student_info = {
'name': 'John Doe',
'age': 20,
'grade': 'A',
'courses': ['Math', 'English', 'Science']
}
# Accessing values
name = student_info['name']
age = student_info['age']
courses = student_info['courses']
# Modifying values
student_info['age'] = 21
# Adding a new key-value pair
student_info['gender'] = 'Male'
# Deleting a key-value pair
del student_info['grade']
# Checking if a key exists
if 'grade' in student_info:
print("Grade information exists.")
else:
print("Grade information does not exist.")
# Displaying keys, values, and items
print("Keys:", student_info.keys())
print("Values:", student_info.values())
print("Items:", student_info.items())
Dictionaries provide a flexible and efficient way to organize and retrieve data based on keys. They are commonly used in various Python applications.
Here is the list of all Dictionary Methods
Method | Description | Syntax |
---|---|---|
copy() | Copy the entire dictionary to new dictionary | dict.copy() |
update() | Update a dictionary by adding a new entry or a key-value pair to anexisting entry or by deleting an existing entry. | Dict.update([other]) |
items() | Returns a list of tuple pairs (Keys, Value) in the dictionary. | dictionary.items() |
sort() | You can sort the elements | dictionary.sort() |
len() | Gives the number of pairs in the dictionary. | len(dict) |
cmp() | Compare the values and keys of two dictionaries | cmp(dict1, dict2) |
Str() | Make a dictionary into a printable string format | Str(dict) |
clear()
:
- Removes all items from the dictionary.
my_dict = {'name': 'John', 'age': 25}
my_dict.clear()
copy()
:
- Returns a shallow copy of the dictionary.
original_dict = {'name': 'John', 'age': 25}
copied_dict = original_dict.copy()
fromkeys()
:
- Creates a new dictionary with specified keys and values.
keys = ['name', 'age', 'city']
default_value = 'unknown'
new_dict = dict.fromkeys(keys, default_value)
get()
:
- Returns the value for the specified key. If the key is not found, it returns a default value (or
None
).
my_dict = {'name': 'John', 'age': 25}
value = my_dict.get('name', 'Default')
items()
:
- Returns a view of key-value pairs as tuples.
my_dict = {'name': 'John', 'age': 25}
items = my_dict.items()
keys()
:
- Returns a view of all keys in the dictionary.
my_dict = {'name': 'John', 'age': 25}
keys = my_dict.keys()
values()
:
- Returns a view of all values in the dictionary.
my_dict = {'name': 'John', 'age': 25}
values = my_dict.values()
pop()
:
- Removes and returns the value for a specified key.
my_dict = {'name': 'John', 'age': 25}
value = my_dict.pop('name')
popitem()
:
- Removes and returns the last key-value pair as a tuple.
my_dict = {'name': 'John', 'age': 25}
key, value = my_dict.popitem()
setdefault()
:
- Returns the value for a specified key. If the key is not found, it inserts the key with a specified default value.
my_dict = {'name': 'John', 'age': 25}
value = my_dict.setdefault('gender', 'Male')
update()
:
- Updates the dictionary with key-value pairs from another dictionary or iterable.
my_dict = {'name': 'John', 'age': 25}
new_data = {'age': 26, 'city': 'New York'}
my_dict.update(new_data)
pop()
:
- Removes and returns the value for a specified key.
my_dict = {'name': 'John', 'age': 25}
value = my_dict.pop('name')
popitem()
:
- Removes and returns the last key-value pair as a tuple.
my_dict = {'name': 'John', 'age': 25}
key, value = my_dict.popitem()
These are just a few of the many dictionary methods available in Python. The official Python documentation is a valuable resource for a comprehensive list of methods and their descriptions: Python Dictionary Methods.